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HORIZONS User Manual Version 3.12 (January 4, 2005)

1. Geometric coordinates Referred to the mean equator and equinox of a particular reference frame ICRF J2000 0 or FK4 B1950 0 Geometric coordinates are the true or instantaneous states of a body at a particular ephemeris time Astrometric coordinates Accounts for the finite but varying amount of time it takes light to travel from the target to the observer and is expressed with respect to the mean equator and equinox of a particular reference frame ICRF J2000 0 or FK4 B1950 0 Apparent coordinates Takes into account factors which appear to change target position with respect to the background stars and inertial coordinate system light time stellar aberration the relativistic deflection of light Usually a final rotation to some of date coordinate system is performed such as precession nutation to true equator and equinox of date Refracted coordinates Apparent coordinates approximately corrected for atmospheric refraction Available only for Earth based sites Small body Refers to a comet or asteroid for which the trajectory is integrated from orbital elements Typically no cartographic coordinate system is available with the exceptions so far being Gaspra and Ida Major body Refers to a planet natural satellite spacecraft or the Sun In special cases a comet or asteroid can be redefined as a major body Only major bodies can be coordinate centers observing sites State vectors are interpolated from previously defined ephem
2. Labels Ob lon Ob lat 15 Solar sub long amp sub lat The planetographic geodetic longitude and latitude of the center of the target disk seen by an observer at the center of the Sun Uses the IAU2000 rotation models For the gas giants only Jupiter Saturn Uranus and Neptune these longitudes are based on the Set Ill prime meridian angle referred to the planet s rotating magnetic field Latitude is always referred to the body dynamical equator Note there can be an offset between the dynamical pole and the magnetic pole Units are DEGREES Labels Sl lon Sl lat 16 Sub Solar Pos Ang amp Dis Target sub solar point position angle CCW with respect to direction of true of date Celestial North Pole and angular distance from the sub observer point center of disk at print time Negative distance indicates the sub solar point is on the hemisphere hidden from the observer Units DEGREES and ARCSECONDS Labels SN ang SN ds 17 N Pole Pos Ang amp Dis Target s North Pole position angle CCW with respect to direction of true of date Celestial North Pole and angular distance from the sub observer point center of disk at print time Negative distance indicates N P on hidden hemisphere Units DEGREES and ARCSECONDS Labels NP ang NP ds 18 Helio eclip lon amp lat Geometric heliocentric J2000 or B1950 ecliptic longitude and latitude of target at the instant light leaves it to be observed at print time print time 1 way lig
3. 3600 will produce output every second Rise set and satellite eclipse circumstances may not be accurate to less than a minute since factors such as the primary s oblateness and atmosphere are not currently modelled Time varying steps Output is typically at fixed time intervals However observer tables may additionally be requested at time varying steps based on an angular shift specification That is output only if the object has moved at least X arcseconds in the plane of sky When specifying step size with the telnet or e mail interfaces respond with something like VAR where is an integer from 60 to 3600 arcseconds This will trigger output whenever the object s position is predicted to be arcseconds different from the current output step in the observer s plane of sky To preserve system performance the time varying output mode uses a simple linear extrapolation to predict the time when the object should have moved the requested distance Due to non linearities in the object s actual motion in the plane of sky this projection can be off by 1 to 5 or more arcsecs Thus the angular motion print criteria you give should be considered approximate Computed quantities will be exact for the given time in the output but the particular output time may not be exactly that required for the requested angular change REFERENCE FRAMES It is necessary to adopt a commonly agreed upon coordinate system for descr
4. from 1799 Jan 1 to 2202 Jan 1 16 Lieske J Precession Matrix Based on IAU 1976 System of Astronomical Constants Astron Astrophys 73 282 284 1979 Precession long term before 1799 Jan 1 and after 2202 Jan 1 17 Owen William M Jr PL A Theory of the Earth s Precession Relative to the Invariable Plane of the Solar System Ph D Dissertation University of Florida 1990 Nutation 18 Table 1 Proposal to the IAU Working Group on Nutation John M Wahr and Martin L Smith 1979 Adopted 1980
5. 10 Earth 399 Moon 301 All others are prograde and must be input with negative longitude east of the adopted prime meridian Since such sites are usually expressed in terms of positive west longitude on maps negative east longitude would be West longitude 360 INTERPRETING NON EARTH OBSERVER TABLES When placing a site on a body other than the Earth some definitions become useful Interfering body The largest other body in the system Such a body can visually complicate observations at the site due to its brightness or by covering up the target On the Earth the interfering body is the Moon On lo it would be Jupiter On Mars it would be Phobos largest body though unlikely to genuinely interfere Mercury and Venus have no interfering bodies Observer tables provide some optional quantities that can be used to characterize the effect of the interfering body or IB how far is the target from the IB in the plane of sky is it obscured by the IB what fraction of the IB is lit by the Sun as seen from the observing site and so on Deflecting body This is the Sun PLUS the most massive object in the planet satellite system e g the system barycenter These two masses are used to compute the relativistic deflection of light that can change the apparent position of the target body Other changes REFRACTION There are no refraction effects modeled for non Earth sites Any request for refraction is ignored and the re
6. J200 0 AD 1620 to AD 1962 Smoothed table UT1 AD 1962 to Present EOP file data UTC For the modern UTC era specifically the calculation is as follows CT UTC CT TAI TAI UTC where CT TAI 32 184 1 657E 3 SIN M 01671 SIN M M 6 239996 T 1 99096871E 7 T CT or TAI seconds past J2000 0 epoch TAI UTC interpolated from current EOP file dropping terms less than about 20 usec in CT TAI As one progresses to earlier times particularly those prior to the 1620 telescopic data span uncertainties in UT determination generally though not always and not uniformly increase due to less precise observations and sparser records At A D 948 uncertainty not necessarily error can be a few minutes At 3000 B C the uncertainty in UT is about 4 hours The TT time scale being uniform does not have this uncertainty but is not directly related to Earth s rotation local time either GREENWICH MEAN SIDEREAL TIME GMST used for topocentric ephemerides is related to UT1 using an expression consistent with the IAU 1976 system of constants as shown on p 50 of the Explanatory Supplement 1992 along with the new more accurate 1997 IAU equinox equation HIGH PRECISION EARTH ORIENTATION PARAMETER EOP MODEL The EOP file is currently updated twice a week based on GPS and other Earth monitoring measurements Horizons uses it to obtain calibrations for UT1 UTC polar motion and nutation correction parameter
7. Satellites of Mars from Spacecraft and Earthbased Observations Astronomy and Astrophysics 225 548 Jacobson R A Riedel J E and Taylor A H 1991 The Orbits of Triton and Nereid from Spacecraft and Earthbased Observations Astronomy and Astrophysics 247 565 Laskar J and Jacobson R A 1987 GUST86 An Analytic Ephemeris of the Uranian Satellites Astronomy and Astrophysics 188 212 Lieske J H 1995 Galilean Satellite Ephemerides E5 JPL Engineering Memorandum 312 583 JPL internal document Owen W M Vaughan R M and Synnott S P 1991 Orbits of the Six New Satellites of Neptune Astronomical Journal 101 1511 Tholen D and Buie M W 1990 Further Analysis of Pluto Charon Mutual Event Observations 1990 Bulletin American Astronomical Society vol 22 No 3 p 1129 Comets and Asteroids Sources of Orbital Elements for Comets and Asteroids l Minor Planet Circulars MPC published by the Minor Planet Center 60 Garden St Cambridge Massachusetts 02138 http cfa www harvard edu cfa ps mpc html The Lowell Observatory Database of Asteroid Orbits E L G Bowell http www lowell edu Solar System Dynamics Group Jet Propulsion Laboratory JPL D K Yeomans Supervisor Cometary Magnitude Parameters 1 2 International Comet Quarterly D W E Green editor 60 Garden St Cambridge Massachusetts 02138 Charles Morris Jet Propulsion Laboratory Pasadena California 91109 Aster
8. amp Y pos ang 20 Obsrv range amp rng rate 34 Local app SOLAR time Local app sid time 21 One Way Light Time 35 Earth gt Site lt time 1 Astrometric RA amp DEC 15 Sun sub long amp sub lat 29 Constellation ID 2 Apparent RA amp DEC 16 Sub Sun Pos Ang amp Dis 30 Delta T CT UT 3 Rates RA amp DEC 17 N Pole Pos Ang amp Dis 31 Obs eclip lon amp lat 4 Apparent AZ amp EL 18 Helio eclip lon amp lat 32 North pole RA amp DEC By Rates AZ amp EL 19 Helio range amp rng rate 33 Galactic latitude 6 7 8 Airmass 22 Speed wrt Sun amp obsrvr gt 36 RA amp DEC uncertainty 9 Vis mag amp Surf Brt 23 Sun Obsrvr Target angl gt 37 POS error ellipse 10 Illuminated fraction 24 Sun Target Obsrvr angl gt 38 POS uncertainty RSS 11 Defect of illumin 25 Targ Obsrv Moon I1llum gt 39 Range amp Rng rate sig 12 Sat angle separ vis 26 Obsr Primary Targ angl gt 40 Doppler delay sigmas 13 Target angular diam 27 Pos Ang radius amp vel 14 Obs sub 1lng amp sub lat 28 Orbit plane angle or select a pre defined format below All quantities B Geocentric only C Small body topo Spacecraft geocentric F Small body geocentric Spacecraft topocentric The alphabetic assignments specifically mean A 1 40 B 1 3 6 9 33 C 1 3 9 11 13 18 29 33 36 40 D 1 5 8 10 11 13 18 29 E 1 3 8 10 18 25 29 F 1 5 8 10 18 25 29 33 34 36 40 with the small body cases primarily s
9. area cet paras O EA Show small body search field names amp meanings NEWS coc cores anges Display program news new capabilities updates etc Pi Oa ai a as Wa Extended help for brief help Program controls LESM oe eee Toggle display of small body match parameter values PAGE oinei aeniei Toggle screen paging scrolling on or off EMAIL X Set your email address to X for output delivery TTY R C Check or reset screen size tty or tty 24 79 to set D AAAA Exit JPL on line system also QUIT or EXIT EE ee ere eee oe Return to the previous prompt back up Short cuts Move backward through the prompts by typing Quit from ANY prompt by entering q To use a default or previously entered value press return After selecting an object enter e to produce an ephemeris format Like the last one without additional prompting SAVING PROGRAM SETTINGS Telnet interactive users may go through program options once then save all settings for recall during future sessions This can save time if you find yourself always changing certain defaults or routinely defining the same output format each time you connect Others in your organization may load and use the same pre defined format settings by name To save program settings go through the prompts and define the settings as you require Then return to the main Horizons gt prompt 1 Type SAVE NAME where NAME cont
10. atari Object GM KM 3 S 2 only a few are known R QRE aaea Perihelion distance AU R ADI ST er Aphelion distance AU R ANGMOM Specific angular momentum AU 2 DAY R pects Neha eee Mean motion DEG DAY R DAN Heliocentric dist AU of ascending node R DDN Heliocentric dist AU of descending node R C esegui Ecliptic longitude of perihelion DEG R B ENE ces Ecliptic latitude of perihelion DEG I NOBS Number of astrometric determinations in solution The next parameters are ASTEROID SPECIFIC If one or more is used the search will conclude faster by examining asteroids only For example including something like H gt 10 will limit the search to asteroids only G ASTNAM Asteroid name fragment designation if unnamed R B V seana B V color asteroid R HI eytegiuriiisin Absolute magnitude parameter asteroid R Gi krete a Magnitude slope parameter can be lt asteroid R ROTPER Rotational period hrs asteroid R ALBEDO Geometric albedo asteroid C STYR assais Spectral type Tholen scheme asteroid The next parameters are COMET SPECIFIC If one or more is used the search will conclude faster by examining comets only For example including something like M1 gt 10 will limit the search to comets only C COMNAM Comet name fragment designation if unnamed I COMNUM Comet number R MI eee Oe este Total absolute magnitude comet R MAr Nuclear absolute magnitude
11. back to you e Web partial access passive interactive GUI interface 1 Point your browser to http ssd jpl nasa gov horizons cgi The Horizons system was intended to be easy to use and should have a step function learning curve The remainder of this documentation summarizes system capabilities but is not necessary for successful use While using the telnet system type or at any prompt for an explanation of options See ACKNOWLEDGEMENTS section for contact information CONNECTING TO THE SYSTEM TELNET The Horizons on line ephemeris and data system is available as a telnet service This is suitable for people who want full access to all program features in an interactive prompt based way From a telnet capable machine preferably running a VT100 type terminal emulation telnet to ssd jpl nasa gov 6775 where 6775 is a port number From within a web browser such as Netscape enter location telnet ssd jpl nasa gov 6775 The system will start a terminal session automatically No user ID or password is required If a user name password is requested you did not specify the port number A few PC type telnet programs seem not to fully implement the telnet protocol and may not pass the port number to the network or may need to be reconfigured to function properly or may have a different syntax for specifying port numbers Consult your user s guide if you have a problem The system will also attempt to
12. follows Labels refers to column headings at the start of the table TIME One output line for each step The line begins with a b if the date is BC a blank if AD This is followed by the date and time which is either UT or TT in calendar or JD format or both depending on user defaults SOLAR PRESENCE Time tag is followed by a blank then a solar presence symbol Daylight refracted solar upper limb on or above apparent horizon C Civil twilight dawn N Nautical twilight dawn A Astronomical twilight dawn Night OR geocentric ephemeris INTERFERING BODYLUNAR PRESENCE The solar presence symbol is immediately followed by another marker symbol m Refracted upper limb of Moon IB on or above apparent horizon Refracted upper limb of Moon IB below apparent horizon OR geocentric ephemeris r Rise target body on or above cut off RTS elevation t Transit target body at or past local maximum RTS elevation s Set target body on or below cut off RTS elevation The rts codes will be displayed under two conditions only if the print interval is less than or equal to 30 minutes or the RTS only print option has been selected For non Earth observing sites no twilight dawn codes C N or A are output refraction is not modelled and the interfering body marker is x instead of the m reserved for Earth s Moon STATISTICAL UNCERTAINTIES Output for asteroids and comets can include formal 3 standard de
13. information projected into the B plane The B plane mentioned above is defined by the three orthogonal unit vectors T R and S the origin being the body center T lies in the B plane pointing in the direction of decreasing celestial longitude R lies in the B plane pointing in the direction of decreasing celestial latitude south S is directed along the relative velocity vector at body encounter perpendicular to the B plane and thus R and T The B vector is the vector in the plane from the body to the point where the incoming object s velocity asymptote pierces the R T plane Note the B plane is defined only when the incoming object is hyperbolic with respect to the body For objects with covariances statistical quantities are output for each close approach All tabulated statistical quantities MinDist MaxDist TCA3Sg Nsigs and P_i p are based on a linearized covariance mapping in which higher order small terms in the variational partial derivatives of the equations of motion are dropped Due to possible non linearities in any given object s actual dynamics this can result in significant errors at epochs distant in time from the solution epoch Consequently long linearized mappings thousands or hundreds or sometimes just dozens of years from the present time should be considered approximate pending additional analysis especially in these cases A objects with numerous close planetary encounters dozens B objects with very clos
14. on non Earth bodies USING A PREDEFINED SITE There are several equivalent ways of specifying a location The most general form is site body where site is a numeric code or name fragment to match and body is a numeric major body code or name fragment to match A list of such major body codes follows later in this document Here are four equivalent ways of searching for the same Earth location Code Meaning 675 399 Site 675 on Earth Palomar Mountain palomar 399 675 Palomar observer table only If an observer table has been requested the may be dropped the Earth will be assumed if an integer like 675 or a name fragment like Palom is input For a vector table the DIFFERENT assumption is made that a coordinate center request lacking a symbol is a major body For example 10 would mean the Caussols site for an observer table but Sun for a vector table 10 or 10 399 would mean the Caussols site for both table types If your specification returns more than one possible match the list of matched sites is returned Refine your site request to be more specific by using numeric codes for example and try again While one can spell out the names of the bodies and sites it is possible unique matches won t be returned Thus use the unique ID numbers when known For example 675 Earth will first look for the body find both the Earth amp Earth Moon barycenter thus have to quit before finding spec
15. produce the ephemeris e MAJOR BODY DATA SCREEN CONSTANTS are from Astrometric and Geometric Properties of Earth and the Solar System Charles Yoder JPL published in Global Earth Physics A Handbook of Physical Constants AGU Reference Shelf 1 e MAJOR BODY DATA SCREEN CONSTANTS are presented for your information FYI only and ARE NOT USED to generate the ephemeris output see below While an effort has been made to insure their accuracy suitability of these DISPLAY constants for any given purpose must be determined by individual users Users should be aware there is often more than one determination in the literature for many of these constants and that they are subject to revision as more data are accumulated LIST OF MAJOR BODY EPHEMERIDES ON LINE The following major body ephemerides are currently on line Newly discovered satellites are also available although they are not shown below Planet centers are considered the 99th satellite of the system barycenter Satellites 506 513 607 716 721 and 802 do not have defined rotational models in the 2000 IAU report 000 Solar System Barycenter 10 Sun 001 Mercury barycenter 199 Mercury 002 Venus barycenter 299 Venus 003 Earth barycenter 399 Earth 301 Moon 004 Mars barycenter 499 Mars 401 Phobo 005 Jupiter b 599 Jupit 501 Io 505 Amalt 509 Sinop 513 Leda 006 Saturn ba 699 Satur 601 Mimas 605 Rhea 609 Phoeb 613 Teles 617 Pando 007 Uranus ba 799 Uranu 701 A
16. 34 bc 278 Jan 12 12 34 B C 12 JAN 278 12 34 The program will interpret other forms as well but if you get too casual you may end up with a surprise interpretation The program s time span prompts indicate the earliest amp latest dates that may be used for the selected target center combination as well as the type of time assumed being input UT CT or TT For cartesian coordinates or osculating elements tables only CT may be used For observer tables output may be either UT or TT TO CHANGE THE UT DEFAULT for observer tables append a TT when entering START time To switch back append a UT to the start time The three time systems are described as follows CT Coordinate Time typically for cartesian and osculating element tables The uniform time scale and independent variable of the ephemerides TT Terrestrial Dynamic Time called TDT prior to 1991 used for observer quantity tables This is proper time as measured by an Earth bound observer and is directly related to atomic time TAI TT periodically differs from CT by at most 0 002 seconds UT is Universal Time This can mean one of two non uniform time scales based on the rotation of the Earth For this program prior to 1962 UT means UT1 After 1962 UT means UTC or Coordinated Universal Time Future UTC leap seconds are not known yet so the closest known leap second correction is used over future time spans TIME ZONE CORRECTIONS Output time tag
17. 4 Metis 516 Helene 612 Caliban 716 no IAU value Sycorax 717 no IAU value Larissa 807 Vesta 20000004 no IAU value Airmass computation is based on 5 Kasten F Young A Revised Optical Air Mass Tables and Approximation Formula Applied Optics vol 28 no 22 p 4735 4738 Nov 15 1989 Refraction computation is based on 6 7 6 Saemundsson T Sky amp Telescope July 1986 p 70 7 Meeus J Astronomical Algorithms 1991 p 101 102 Constellation identification based on 8 9 10 11 8 Roman N G 1987 Identification of a Constellation from a Position Publ Astronomical Society of the Pacific 99 695 699 9 Warren Wayne H Jr 1997 GSFC private communication 10 Delporte E 1930 Delimitation Scientifique des Constellations Cambridge Cambridge University Press 11 Gould B A 1877 Uranometria Argentina mapas Buenos Aires Argentina Observatorio Nacional Long term CT UT offset calculations based on 12 priv comm Morrison 1980 13 Stephenson F R Houlden M A Atlas of Historical Eclipse Maps Cambridge Univ Press p X 1986 14 Stephenson F R Morrison L V Long term Changes in the Rotation of the Earth 700 B C to A D 1980 Phil Trans R Soc London 313 47 70 1984 15 Stephenson F R Morrison L V Long term Fluctuations in the Earth s Rotation 700 BC to AD 1990 Phil Trans R Soc London 351 p 165 202 1995 Precession IAU
18. 5 EC 8241907231263196 QR 532013766859137 TP 2450077 480966184235 OM 89 14262290335057 W 326 0591239257098 IN 4 247821264821585 Al 5 113711376907895D 10 A2 6 288085687976327D 10 CUSTOMIZING REQUESTED EPHEMERIDES Keys are embedded in output ephemerides to assist with automated reading of the output by user s own software The keys are defined as follows SOE Start of ephemeris EOE End of ephemeris Ephemerides may be customized by changing output default flags The symbols below denote login defaults All tables may be optionally output in a comma separated value format for import into spreadsheets 1 Cartesian state vector table Any object with respect to any major body Reference frame i J2000 ICRF J2000 0 B1950 FK4 B1950 0 Coordinate system Earth mean equator and equinox of frame Epoch J2000 0 or B1950 0 s Ecliptic and mean equinox of frame Epoch J2000 0 or B1950 0 Central body mean equator and node of date Aberration corrections NONE geometric state vectors LT Light time LT S light time amp stellar aberration Units KM and seconds KM and days AU and days Quantities Output 1 Position components x y z only 2 State vector x y Z Vvx vy vz 3 State vector 1l way light time range range rate 4 Position 1l way light time range range rate 5 Velocity components vx vy vz only 6 l way light time range range rate 2 Osculating elements table Any
19. 54 2127 A particular object s orbit may be insufficiently well determined over the chosen time span to be suitable for some high precision purposes Background SPK files can be produced only with the telnet interface Horizons allows a maximum of 20 small bodies per SPK file To construct an SPK for a comet or asteroid Horizons integrates the object s trajectory over a user specified time span greater than 32 days but less than 200 years The position components at discrete steps over some interval are fit to a series of Chebyshev polynomials When a users application program reads the SPK file the appropriate polynomials are accessed and interpolated to retrieve the requested state SPK files are capable of storing trajectory data with a fidelity greater than 1 millimeter more accurately than should ever be required In practice it is the Chebyshev fit that determines how closely the SPK interpolation matches the integrator The typical trade off is that higher fidelity SPK files are obtained by fitting higher degree polynomials to smaller time intervals The cost for increased accuracy is larger file size File Fidelity Choosing the best way to represent a trajectory in a file is complicated by the wide range of small body orbits and anomalies such as close approaches to major planets Horizons seeks to strike a rough balance between file size and file fidelity valuing fidelity more than file size Prior to the integration a def
20. HORIZONS User Manual Version 3 12 January 4 2005 Table of Contents e Introduction e Purpose e Overview of Usage e Connecting to the System e General Definitions e Object Selection e Categories e Major Body Selection e Small Body Selection e Coordinate Center Observing Site Selection e Earth Sites e non Earth Sites e Using a Predefined Site e Input of Topocentric Site Coordinates e Interpreting non Earth Observer Tables e Limitations of non Earth Moon Rotation Models e Other Main Prompt Commands e Saving Program Settings e Integrator Display e Specification of Time e Time Zone Corrections e Output Stepping e Coordinate Reference Frames e ICRF J2000 e FK4 B1950 INTRODUCTION PURPOSE Coordinate Systems Searching for Small Bodies User Specified Small Bodies Customizing Requested Ephemeris Definition of Observer Table Quantities e Statistical Uncertainties e Specific Quantities Close Approach Tables Understanding Rise Transit and Set Indicators Constellation Identification SPK File Generation Statement of Ephemeris Limitations Long Term Ephemeris Background Asteroid Observer Ephemeris 1 Ceres Sources and References for Primary Ephemeris Data Acknowledgements Appendices Examples e Major body data screen e Asteroid data screen e Comet data screen e Small body search e Satellite Observer Ephemeris lo The JPL Horizons O
21. XT Request ASCII plain text version of current documentation DOC PS Request PostScript version of current documentation BATCH LONG Request Latest fully commented example batch file BATCH BRIEF Request latest example batch file without comments QUESTION Message forwarded to cognizant engineer GENERAL DEFINITIONS The remainder of this document uses these abbreviations and terms Understanding their meaning will help you properly interpret program documentation and output RA Right ascension the angular distance on the celestial sohere eastward along the celestial equator from the reference equinox to the meridian of the object RA is analogous to longitude with the plane containing the equinox defining zero RA much as the Greenwich meridian defines zero longitude Expressed in units of hours minutes and seconds or degrees as requested DEC Declination the angular distance on the celestial sphere north positive or south negative of the celestial equator It is analogous to latitude Usually expressed in degrees AZ Azimuth the angle measured eastward along the horizon the plane perpendicular to the local zenith from the North to the point where the meridian passing through local zenith and the object intersects the horizon plane EL Elevation the angular distance above or below the plane perpendicular to the local zenith Note this plane is not necessarily the visible horizon due to station elevation horizon dip effect
22. ains 1 12 characters 2 Next time you telnet to Horizons type LOAD NAME Your output preferences will then be loaded in as the new defaults If you make a mistake or want to change a setting later two commands are relevant DELETE and SAVE DELETE a macro with command DELETE NAME Alternatively change specific settings manually then replace the stored macro with a SAVE to an existing name Delete and replace operations require input of a confirming password LOAD does not Thus anyone can use your settings if they know the macro name Only those who know the password can change or delete a macro Start stop dates are also saved in the macro as is observing location You need only load the macro and select the target Remaining defaults will be as defined in the format macro If the macro is for an individual personal use you may want to set the e mail address prior to saving Otherwise don t so users of the macro will be prompted for it in the future A macro may be loaded then specific settings overruled by responding to the program prompts For example if your last table prior to saving the macro was a vector table that table type will be saved as the default Settings for the other table types are saved as well so to access them manually respond to the prompt requesting table type over riding the macro s vector default on that issue Start and stop times are also macro settings that may commonly be overruled as necessar
23. an equator at the reference epoch Z axis along the Earth mean north pole at the reference epoch Body true equator and Earth equinox of date apparent coordinates Reference epoch of date xy plane plane of the body s true equator at the reference epoch X axis out along ascending node of instantaneous plane of the Earth s orbit and the Earth s true equator plane at the reference epoch Z axis along the body s true north pole at the reference epoch SEARCHING FOR SMALL BODIES Search for small bodies with following keywords Type R real I integer C char Use comparisons from the set lt gt lt gt Separate each field with a semi colon Example search formulation A lt 2 5 IN gt 7 8 STYP S GM lt gt 0 The first group of keywords are common to asteroids AND comets Type Keyword Description C NAME Asteroid OR comet name fragment C DES ananin Object designation R EPOCH Julian Date of osculating elements R CALEPO Calendar date of osc elements YYYYMMDD ffff R rere ere wren Semi major axis AU R Coen eerie Eccentricity R EN morier Inclination of orbit plane DEG wrt ecliptic R OMH anpe Longitude of Ascending Node DEG wrt ecliptic equinox R s E Argument of Perihelion DEG wrt ecliptic equinox R ER ariede Perihelion Julian Date R CALTE sities Perihelion calendar date YYYYMMDD ffff R MA eiaeia ie Mean anomaly DEG R PER ssaa Orbital period YRS R RAD raver Object radius KM R GM
24. and Rotational Elements of the Planets and Satellites 2000 Celestial Mechanics and Dynamical Astronomy 82 83 110 2002 2 The Astronomical Almanac 1993 3 Planetary Geodetic Control Using Satellite Imaging Journal of Geophysical Research Vol 84 No B3 March 10 1979 by Thomas C Duxbury 4 Letter from Thomas C Duxbury to Dr Ephraim Lazeryevich Akim Keldish Institute of Applied Mathematics USSR Academy of Sciences Moscow USSR Most values are from the IAU IAG Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites 2000 The exceptions are e Radii for the Sun are from the above reference 2 e The second nutation precession angle M2 for Mars is represented by a quadratic polynomial in the IAU2000 report Current software cannot handle this term which is extremely small so the polynomial is truncated to a linear one e The expressions for the pole and prime meridian of Neptune given in the IAU report include trigonometric terms which current software doesn t yet handle These terms are omitted e For several satellites the I AU2000 report either gives a single radius value or a polar radius and a single equatorial radius Current software uses a triaxial ellipsoid model that requires three radii In the cases listed below additional values have been supplied in order to allow the software to function The affected satellites are Body NAIF ID code Thebe 51
25. ault mesh state vector interval is selected for the polynomial fits There is the loose mesh for main belt objects eccentricity less than 0 35 semi major axis greater than 2 3 AU This covers the majority of objects Integrator states are preserved to the meter level or less 1 sigma for most objects There is a standard mesh that will fit all but a few objects well close approaches are described accurately to the 10 50 meter range and lt 1 meter at other times File sizes are 4 times larger than loose mesh objects Finally for a few objects a tight mesh will be necessary File sizes are 4x larger than standard 16x larger than loose Mesh assignment is automatic but not all cases requiring a tight mesh can be detected in advance which is why this is being discussed At the end of an integration a summary of polynomial fit maximum errors is displayed FHFHFHFHFFHFHFHFHFHPHPFEEEPEPEEPEEPEEEEEEPPEPETEPEPE PE EFT A posteriori SPK fidelity estimate rel to integrator Max error 3 std dev Time X 0 7104212997280315D 03 m 1998 May 09 12 00 00 000 Y 0 1287005692494599D 02 m 1998 May 09 12 00 00 000 Z 0 7502616895491441D 03 m 1998 May 09 12 00 00 000 RSS 0 1650446811753079D 02 m 1998 May 09 12 00 00 000 FHFFHHFHHFFFHHFHTHFFFFEPEEPEPEETTEEEEEEETEPEEETEEEEEE PEF This shows the maximum three standard deviation error detected in the Chebyshev fit to the integrator position vector components The maximum root sum square RSS
26. cludes Charon The Sun s altitude above the Saturn ring plane is not considered for Saturn When the Moon is at phase angles lt 7 deg within 1 day of full the computed magnitude tends to be 0 12 too small Surface brightness is returned for asteroids only if a radius is known It is the average visual magnitude of a square arcsecond of the illuminated portion of the apparent disk For observing sites not on the Earth or Moon planet and satellite values are not available Sun comet and asteroid values are Units are none and VISUAL MAGNITUDES PER SQUARE ARCSECOND Magnitude laws Sun APmag M 5 5 l0og10 d where M 4 83 d distance from Sun parsecs Asteroids APmag H 5 logl delta 5 log10 r 2 5 1lo0g10 1 G phil G phi2 Comets T mag M1 5 1logl0 delta k1 log10 r N mag M2 5 logl0 delta k2 log10 r phcof beta Surface brightness S brt V 2 5 10g10 k PI a b Labels APmag S brt Non comet with Known dimensions APmag Non comet with unknown dimensions T mag N mag comets total amp nuclear magnitudes 10 Illuminated fraction Percent of target object circular disk illuminated by Sun phase as seen by observer Units are PERCENT Labels Illu 11 Defect of illumination Angular width of target circular disk diameter not illuminated by Sun Available only if target radius is known Units are ARCSECONDS Labels Def_illu 12 Angular separation visibility The angle between the center of a non
27. comet R KI irai eee Total magnitude scaling factor comet R K2 eeen Nuclear magnitude scaling factor comet R PHCOF Phase coefficient for k2 5 comet R Ady eo a Radial non grav accel comet 10 8 AU DAY 2 R AQ aai Transverse non grav accel comet 10 8 AU DAY 2 R AF fad eveaus Normal non grav accel comet AU d 2 R DT aereas Non grav lag delay parameter comet days Only 1 of the 4 keywords ASTNAM COMNAM NAME or DES can be specified on a given search Directives There are 3 directives that may be used to limit or control searches Directive Description COMH azesssise Limit search to comets only AST srssa Limit search to asteroids only LIST Display parameter values for matched objects This may be set as a default for all subsequent searches by typing LIST at the main system prompt Horizons gt For example A lt 2 5 IN gt 10 AST match parameters against asteroids ONLY A lt 2 5 IN gt 10 AST LIST match AND display values of the parameters Contents of Small body Database Excluded from the database are single opposition asteroids with observational data arcs less than 30 days unless they are NEO s PHA s or radar targets which ARE included Everything else is in Except for PHA s and NEOs which are usually included within a couple hours of announcement there can be a delay of a few days toa couple weeks before newly discovered objects that meet the fil
28. d ephemeris covers the interval from 3000 B C to A D 3000 This ephemeris is identical to the shorter DE 405 in the sense it is the same data fit solution and the same numerical integration as DE 405 However it has been stored with slightly less accuracy to reduce its size For the Moon DE 406 recovers the original integrator state to within 1 meter other bodies within 25 meters maximum error This difference can be less than the uncertainty associated with the trajectory solution itself thus is insignificant for all but the most specialized circumstances The short span version DE 405 recovers the integrator state to the millimeter level Horizons uses the long term DE 406 LE 406 for the following objects Objects ID code All planet barycenters 0 1 2 3 4 5 6 7 8 9 Sun 10 Moon 301 Mercury 199 Venus 299 Earth 399 Mars 499 Satellites and outer solar system planet centers each have various shorter intervals as warranted by their observational data arc Comets and asteroids are available only over the A D 1599 to A D 2200 interval of the DE 405 ephemeris they are integrated against Only a few dozen small bodies have sufficiently well known orbits to justify rigorous integration over time spans of hundreds of years PRECESSION MODEL For the time span of 1799 Jan 1 to 2202 Jan 1 the official IAU precession model 16 of Lieske is used As published this model is valid for only 200 years on either side of the J2000 0 e
29. determine your window size If it cannot it will default to a 24 row by 79 column screen display If this is inappropriate and your display paging is choppy manually set your screen size by using the command TTY rows columns where rows and columns are replaced by appropriate integers Window sizes less than 79 columns aren t recommended since data screen displays are formatted with that minimum size in mind and will be difficult to read on something smaller WEB Point your browser to http ssd jpl nasa gov horizons cgi This graphical interface is intended for the more casual user or general public and offers access to a subset of program features using pull down menus fill in boxes and buttons to click E MAIL The program can also be controlled by sending e mail messages to the address horizons ssd jpl nasa gov Response is determined by the subject of the message This option is for those who want access to most program features without the overhead of answering prompts or manipulating graphical interfaces generally those already familiar with what the program does and who know what they want To get started send e mail to the above address with the subject BATCH LONG The latest fully commented example run stream will be mailed back Edit this file to produce the results you want then mail back with the subject JOB Acceptable e mail subject commands are SUBJECT HEADER MEANING JOB Horizons run stream DOC TE
30. e planetary encounters lt 0 01 AU C objects with very short data arcs days or weeks While linearized projections will tend to indicate such cases with obviously rapid uncertainty growth the specific numbers output can tend to understate orbit uncertainty knowledge Possible output quantities are described below Nominal effectively means highest probability for the given orbit solution although there can be other possible orbits of equal probability If there is no covariance no statistical quantities are returned Date CT Nominal close approach date Coordinate Time Calendar dates prior to 1582 Oct 15 are in the Julian calendar system Later calendar dates are in the Gregorian system Body Name or abbreviation of the planetary body or major asteroid being closely approached by the selected small body CA Dist Nominal close approach distance at the close approach time Units AU MinDist Minimum close approach distance possible formal 3 standard deviations with linearized covariance mapping Units AU MaxDist Maximum close approach distance possible formal 3 standard deviations with linearized covariance mapping Units AU Vrel Relative velocity of the object and the body it is approaching at the nominal time of close approach Units KM S TCA3Sg Close approach time 3 standard deviation uncertainty Units MINUTES SMaA 3 sigma error ellipse semi major axis projected into the B plane at nomi
31. eXT among others Incompatible systems Known incompatible machines would be the Intel series 80486 Pentium etc DEC Alpha and VAX which have reversed byte orders and or non lEEE floating point To obtain an SPK for one of these platforms respond yes to the transfer format prompt The binary file will be converted to a transfer file Once you FTP this file to your system using FTP ASCII mode you MUST run the program spacit or tobin included in your SPICE Toolkit to produce a binary compatible SPK for your machine STATEMENT OF EPHEMERIS LIMITATIONS To produce an ephemeris observational data optical VLBI radar amp spacecraft containing measurement errors are combined with dynamical models containing modeling imprecisions A best fit is developed to statistically minimize those errors The resulting ephemeris has an associated uncertainty that fluctuates with time For example only a limited percentage of asteroid orbits are known to better than 1 arcsec in the plane of sky over significant periods of time While 1991 JX center of mass was known to within 30 meters along the line of sight during the 1995 Goldstone radar experiment errors increase outside that time span Uncertainties in major planet ephemerides range from 10cm to 100 km in the state of the art JPL DE 405 ephemeris used as the basis for spacecraft navigation mission planning and radar astronomy Cartesian state vectors are output in all their 16 d
32. ecimal place glory This does not mean all digits are physically meaningful The full precision may be of interest to those studying the ephemerides or as a source of initial conditions for subsequent integrations On top of this basic uncertainty for osculating element output GM is rarely known to better than 5 significant figures For observer angular output tables purely local atmospheric conditions will affect refraction corrected apparent places by several arcseconds more at the horizon Small body elements are reported in the optical frame i e FK5 J2000 0 This frame is currently thought to differ by no more than 0 01 arcseconds from the radio frame ICRF93 J2000 0 of the planetary ephemeris DE 405 Until a generally agreed upon transformation from one frame to the other is defined and implemented they will be treated by this program as being the same The Earth is assumed to be a rigid body and solid Earth tides affecting station location are not included Of course precession and nutation effects are included as is polar motion CT TAI terms less than 20 usec are omitted These and other Earth model approximations result in topocentric station location errors with respect to the reference ellipsoid of less than 20 meters However many optical site positions latitude and longitude are known far less accurately and can be many kilometers off Relativistic effects are included in all planet lunar and small body dynamics excluding
33. eda 512 Saturn Hyperion 607 Uranus Caliban 716 Sycorax 717 Neptune Nereid 802 After coordinate input is requested the site location may be entered as either geodetic or cylindrical coordinate triplets separated by commas GEODETIC generally this means map coordinates E long Geodetic east Longitude DEGREES lat Geodetic latitude DEGREES h Altitude above reference ellipsoid km CYLINDRICAL E long Angle eastward from XZ plane DEGREES DXY Distance from Z axis KM DZ Height above XY equator plane KM This system always uses planetographic geodetic coordinates This is typically the one used on maps such as those by the USGS unless the map says otherwise In these coordinates the rotational pole of the body that lies on the positive north side of the invariable plane of the solar system the plane perpendicular to the solar system s angular momentum vector is called the north pole Northern latitudes are positive southern are negative The planetographic latitude takes into account body oblateness and for a point on the surface is the angle between the body equatorial plane and the normal to the reference surface at that point For a point not on the reference surface the geodetic latitude is the latitude of the point on the reference surface where the normal passes through the point at some altitude h above the reference surface Prograde or direct rotation of a body is rotation east
34. eference epoch Reference epoch J2000 0 or B1950 0 xy plane plane of the Earth s mean equator at the reference epoch x axis out along ascending node of the instantaneous plane of the Earth s orbit and the Earth s mean equator at the reference epoch z axis along the Earth mean north pole at the reference epoch Ecliptic and mean equinox of reference epoch Reference epoch J2000 0 or B1950 0 xy plane plane of the Earth s orbit at the reference epoch X axis out along ascending node of instantaneous plane of the Earth s orbit and the Earth s mean equator at the reference epoch z axis perpendicular to the xy plane in the directional or sense of Earth s north pole at the reference epoch Body mean equator and node of date Reference epoch of date Reference plane ICRF J2000 0 or FK4 B1950 0 xy plane central body mean equator plane at reference epoch X axis out along the ascending node of the central body mean equator plane on the reference plane at the reference epoch Z axis along the central body mean north pole at the reference epoch OBSERVER TABLE COORDINATES such as RA and DEC may be with respect to two possible coordinate systems Earth mean equator and equinox of reference epoch astrometric coordinates Reference epoch J2000 0 or B1950 0 xy plane plane of the Earth s mean equator at the reference epoch X axis out along ascending node of the instantaneous plane of the Earth s orbit and the Earth s me
35. er and 301 is the center of the Moon For Mercury Venus and Mars there is no significant difference between planet center and system barycenter 1 199 2 299 4 499 etc If a planet name is entered it may not be considered unique if a distinct system barycenter is present For example if Saturn is entered a list containing Saturn and the Saturn Barycenter will be returned To specify Saturn the planet center you must use its unique ID code 699 System barycenters are available over longer time spans than planet centers SMALL BODIES To select an asteroid or comet enter a list of parameters to search on SEPARATED BY A SEMI COLON TYPE SB FOR LIST OF 40 FIELD KEYWORDS THAT CAN BE MATCHED or see list later in this document Match symbols are from the set gt lt lt gt Examples at the main prompt Horizons gt A lt 2 5 IN gt 7 8 STYP S GM lt gt 0 match parameters Horizons gt Vesta or ASTNAM Vesta for faster search Horizons gt DES 1993 Objects with designations containing 1993 Horizons gt 1 Object in file position 1 Horizons gt Enter your own elements For example A lt 2 5 IN gt 7 8 STYP S GM lt gt 0 searches for all S type small bodies with semi major axis less than 2 5 AU and inclination greater than 7 8 degrees with a known non zero GM Spaces in the command are not considered nor are upper lower case distinctions Exceptions are object na
36. erides such as DE 405 which are stored as Chebyshev coefficients Interpolation recovers the state the mm level Target body Refers to the object of interest selected by the user It can be a major body or small body Primary body Refers to closest body about which a target body orbits For natural satellites this would be a planet although they orbit the Sun as well For planets and small bodies the primary body is the Sun OBJECT SELECTION Effective use of this system requires knowledge of how to select objects The two classes of objects accessed slightly differently are the major bodies planets and satellites and small bodies comets and asteroids Accessing the different object types is described in the sections below MAJOR BODIES Type MB to get a list of all major body strings that can be used to search on To select a major body enter one of the following 1 A string to search on Mars or Trit 2 AJPLID integer code or fragment 3 An IAU code Examples at the main prompt Horizons gt mars uniquely select Mars center 499 does same Horizons gt 501 uniquely select Io Horizons gt N list all major bodies with n in an ID field Major planets may have two integer ID s Those gt 100 ending in 99 such as 199 299 399 etc refer to planet CENTERS To select planet SYSTEM BARYCENTERS use the codes less than 10 1 2 3 For example 399 is the Earth s center 3 is the Earth Moon Barycent
37. fraction angle will be zero This affects rise set determination on non Earth bodies as well AIRMASS There is no airmass model or airmass cut off available for non Earth sites Any request for airmass computation is ignored APPARENT RA amp DEC The origin of Right Ascension for apparent coordinates on NON EARTH sites with rotational models is the meridian containing the Earth equinox of J2000 0 Apparent declination is with respect to the particular body s true equator of date This allows an observer to align axes with the pole and use the local apparent sidereal time output by this system to set the RA origin and acquire the target For objects lacking a pole amp prime meridian rotational model spacecraft and certain asteroids that may have been redefined as major bodies the reference frame ICRF J2000 0 or FK4 B1950 0 coordinate system is used to compute apparent places That is apparent RA and DEC are defined with respect to the Earth mean equator and equinox of the frame epoch TIME The print time output by this system for observer tables UT or TT is the instantaneous time on Earth For non Earth sites it is unrelated to the rotation of the body Local apparent solar time at the observing site can be requested as can the instantaneous light time from Earth to the non Earth site LIMITATIONS OF NON EARTH MOON ROTATION MODELS For bodies outside the Earth Moon system precession and nutation effects are usually not
38. ht time Units DEGREES Labels hEcl Lon hEcl Lat 19 Helio range amp range rate Target apparent heliocentric range r and range rate rdot as seen by the observer Units are AU and KM S Labels r rdot 20 Observer range amp range rate Target apparent range delta amp range rate delta dot relative to observer Units are AU and KM S Labels delta deldot 21 One Way Light time Target 1 way light time as seen by observer The elapsed time since light observed at print time left or reflected off the target Units are MINUTES Labels 1 way_LT 22 Speed wrt Sun amp obsrvr Magnitude of velocity of target with respect to the Sun center and the observer at the time light left the target to be observed Units are KM S Labels VmagSn Vmag0b 23 Sun Observer Target angle Target s apparent solar elongation seen from observer location at print time If negative the target center is behind the Sun Units are DEGREES For observing centers with defined rotation models an additional marker is output under the column labelled r for relative position If there is no rotation model associated with the observing center no r column will be present Under this column T indicates target trails Sun evening sky L indicates target leads Sun morning sky NOTE The S O T solar elongation angle is the total separation in any direction It does not indicate the angle of Sun leading or trailing Labels S O T
39. hysical aspect angles etc Osculating elements Cartesian state vectors Close approaches to planets and Ceres Pallas and Vesta SPK binaries asteroids and comets only Sw The first four are ASCII tables Output is returned to the user via e mail FTP or Kermit protocols Table output can be requested in a format suitable for spreadsheet import SPK file output allows user programs to reproduce the integrated target state at any instant The SPK files can be used by existing visualization animation and mission design software The underlying planet satellite ephemerides and small body osculating elements are the same ones used at JPL for radar astronomy mission planning and spacecraft navigation OVERVIEW OF USAGE There are three different ways to access the program e Telnet full access active interactive prompt based interface 1 Telnet directly to the system telnet ssd jpl nasa gov 6775 No account or password is required 2 Specify an object to get a summary data screen 3 Follow prompts At any prompt type or for short and long explanations 4 Transmit results to your system by e mail FTP or Kermit e E mail full access except for SPK file production batch interface 1 Send e mail to horizons ssd jpl nasa gov with subject BATCH LONG 2 An example command file will be mailed back to you 3 Edit this text file then mail it back with the subject header JOB 4 Results of your request are mailed
40. ibing the position and velocity of an object in three dimensional space This program has two basic frames available the default is ICRF J2000 0 which can be changed to FK4 B1950 0 if desired at the appropriate prompt J2000 selects an Earth Mean Equator and dynamical Equinox of Epoch J2000 0 inertial reference system where the Epoch of J2000 0 is the Julian date 2451545 0 Mean indicates nutation effects are ignored in the frame definition The system is aligned with the IAU sponsored J2000 frame of the Radio Source Catalog of the International Earth Rotational Service ICRF The ICRF is thought to differ from FK5 by at most 0 01 arcsec J2000 0 reference vectors have the following properties e Z is normal to ICRF Mean Earth Equator of Epoch J2000 0 e X is parallel to ICRF Mean Earth Dynamical Equinox of Epoch J2000 0 e Y completes the right handed system B1950 selects an inertial reference frame based on Earth Mean Equator and FK4 catalog Equinox of Epoch B1950 0 FK4 B1950 0 where the Epoch of B1950 0 is the Julian date at the start of the Besselian year B1950 0 2433282 42345905 The Fricke equinox correction at Epoch is applied COORDINATE SYSTEMS CARTESIAN VECTORS and OSCULATING ELEMENTS may be requested in one of three available coordinates systems derived from the selected basic reference frame These systems are defined with respect to the reference frames above as follows Earth mean equator and equinox of r
41. ific Palomar site coordinates 675 399 is unique and avoids this problem Spaces amp upper lower case are ignored Here are examples for sites on bodies other than the Earth Viking 499 List all defined Viking lander sites on Mars Viking 1 499 Select Viking 1 landing site on Mars 1 301 Site 1 on the Moon 500 501 lo body center 3 499 Site 3 on Mars The asterisk can be used to generate lists Code Meaning 301 List all predefined sites on the Moon Phobos List all predefined sites on the Martian moon Phobos 399 List all predefined sites on Earth List all predefined sites on Earth observer vector table X List all predefined sites on Earth observer vector table List all major bodies element table only There are a several ways to request a body centered site for a major body Code Meaning 5000601 Mimas body center geo 601 g 601 g Mimas g 500 Deimos Deimos body center geo Earth Geocenter g 399 Earth Geocenter INPUT OF TOPOCENTRIC SITE COORDINATES For sites with IAU rotation models topocentric sites may be input by the user as follows Code Meaning c Europa Request prompting for user location on satellite Europa coord 502 same The following satellites DO NOT have rotation models thus do not support topocentric site definition Only body centered observers can be defined Jupiter Himalia 506 Elara 507 Pasiphae 508 Sinope 509 Lysithea 510 Carme 511 Ananke 512 L
42. ion time leaves the target Positive values indicate observer is above the object s orbital plane in the direction of reference frame z axis Small bodies only Units DEGREES Labels PlAng 29 Constellation ID The 3 letter abbreviation for the constellation name of target s astrometric position as defined by the IAU 1930 boundary delineation Labels Cnst 30 CT UT Difference between uniform Coordinate Time scale ephemeris time a Earth rotation dependent Universal Time Prior to 1962 the difference is with respect to UT1 CT UT1 For 1962 and later the delta is with respect to UTC CT UTC Values beyond the next July or January 1st may change if a leap second is introduced at later date Units SECONDS Labels CT UT 31 Observer Ecliptic Longitude amp Latitude Observer centered ecliptic of date longitude and latitude of the target s apparent position corrected for light time the gravitational deflection of light and stellar aberration The ecliptic plane is the Earth s orbital plane at print time Units DEGREES Labels ObsEcLon ObsEcLat 32 Target North Pole RA amp DEC Right Ascension and Declination IAU2000 rotation model of target body s North Pole direction at the time light left the body to be observed at print time Consistent with requested reference frame ICRF J2000 0 or FK4 B1950 0 RA and DEC Units DEGREES Labels N Pole RA N Pole DC 33 Galactic Latitude Observer centered Galactic System II po
43. ions within a given integration step are performed to compute states at closely spaced print times The last number on the integrator display line is the most recent step size in days SPECIFICATION OF TIME ACCEPTED FORMATS Time may be specified many ways in addition to the primary form YYYY MMM DD HH MM Of particular note are Julian day number and day of year forms Examples are shown below Input start times may be specified to 1 1000th of a second if the default output setting is changed from minutes Generally if the input start time has more digits of precision specified than the selected output format start time will be truncated to the appropriate level For example if a start time of 23 45 12 4 is specified but the output format is only set to minutes start time will automatically be changed to 23 45 00 000 YOUR INPUT PROGRAM INTERPRETATION Recommended 1997 May 5 12 30 23 3348 5 MAY 1997 12 30 23 334 Acceptable 1 9 96 3 12 59 2 9 JAN 1996 03 13 19 96 3 12 59 2 9 JAN 1996 03 13 2 jan 91 3 00 12 2 2 JAN 1991 03 00 91 MAR 10 12 00 00 10 MAR 1991 12 00 29 February 1975 3 00 1 MAR 1975 03 00 10 October 29 3 58 29 OCT 2010 03 58 dec 31 86 12 31 DEC 1986 12 00 86 365 12 31 DEC 1986 12 00 JUL 98 1 JUL 1998 00 00 JD 2451545 1 JAN 2000 12 00 JD2451545 1 JAN 2000 12 00 278bc jan 12 12 34 B C 12 JAN 278 12 34 AD 99 Aug 12 12 34 A D 12 JAN 99 12
44. kipping cartographic dependent quantities Note that Ida and Gaspra are exceptions having IAU defined mapping grids so that C amp D options won t provide all available data for such objects In the list below indicates initial program default settings Reference coordinate frame J2000 ICRF J2000 0 B1950 FK4 B1950 0 Body true equator and Earth equinox of date Time scale z UT Universal Time TT Terrestrial Time Time zone correction used for UT based tables only Time format Calendar JD Julian date Both Time output precision calendar format only MINUTES HH MM SECONDS HH MM SS FRACSEC HH MM SS fff Right ascension format F Hours minutes seconds of arc DEC degrees minutes seconds Decimal degrees High precision RA DEC output No 10 2 arcsec HH MM SS ff DD MM SS f Yes 10 4 arcsec HH MM SS ffff DD MM SS fff Apparent coordinate corrections s Airless apparent Refracted apparent Minimum elevation integer value 90 degrees Maximum airmass real value id 38 0 refracted elevation 0 deg Rise Transit Set print ONLY No TVH True visual horizon Includes dip and refraction Earth only GEO Geometric horizon Includes refraction Earth only RAD Radar horizon Geometric horizon no refraction Skip Daylight No Yes DEFINITION OF OBSERVER TABLE QUANTITIES The menu of observer table output quantities was shown above The format of the table is as
45. known to high accuracy Thus the NON Earth Moon IAU rotation models used by this system to determine topocentric site motion relative to the inertial frame as a function of time are good to about 0 1 degree in the present era For the gas giants Jupiter Saturn Uranus and Neptune IAU longitude is based on the Set III prime meridian rotation angle of the magnetic field By contrast pole direction thus latitude is relative to the body dynamical equator There can be an offset between the magnetic pole and the dynamical pole of rotation For many satellites and the planet Mercury the official IAU pole direction was simply assumed perpendicular to the body s mean orbit plane lacking better information For many satellites in the IAU model the rotation rate was assumed equal to the mean orbital period Some small satellite rotational models are strictly valid only at the time of the Voyager spacecraft flyby extrapolation to other times is hazardous Topocentric results for such bodies 610 614 for example should be used cautiously if at all Results in these cases reflect only the best available model which is a suspect one As rotation models are refined through observation of surface features by visiting spacecraft Cassini etc Horizons will be updated to use the best officially sanctioned models available OTHER COMMANDS Program information MBM sa Sena See NS Show planet natural satellite major body ID fields SB tet
46. lian 1582 Oct 03 2299158 5 Julian 1582 Oct 04 2299159 5 gt skipped 1582 Oct 05 2299160 5 skipped 1582 Oct 06 2299151 5 skipped 1582 Oct 07 2299152 5 skipped 1582 Oct 08 2299153 5 skipped 1582 Oct 09 2299154 5 skipped 1582 Oct 10 2299155 5 skipped 1582 Oct 11 2299156 5 skipped 1582 Oct 12 2299157 5 skipped 1582 Oct 13 2299158 5 skipped 1582 Oct 14 2299159 5 Gregorian 1582 Oct 15 2299160 5 lt Gregorian 1582 Oct 16 2299161 5 Gregorian 1582 Oct 17 2299162 5 Note that Julian calendar dates are different than and unrelated to Julian day numbers Examination of this table shows that the date labels from Oct 5 1582 through Oct 14 1582 don t exist Of course the days themselves do as is shown in the continuous Julian day number column it s just a matter of what one calls them If you specify a non existent calendar date label that was skipped this program will automatically use a day number as shown above that maps into the previous Julian calendar system For example requesting a date of 1582 Oct 14 skipped is the same as requesting the Julian calendar date 1582 Oct 04 ANCIENT DATES Objects 0 10 199 299 301 399 and 499 planet barycenters their equivalents and the Sun amp Moon are available over a 3000 B C to A D 3000 interval When specifying ancient calendar dates this system requires input in the BC AD scheme If no BC marker is input with a calendar date it i
47. llipse Numerical Integration Numerical Integration GUST Analytic Precessing ellipse Numerical Integration Numerical Integration Precessing ellipse Dynamic conic References For Natural Satellite Ephemerides 1 Jacobson R A 1991 Outer Jovian Satellite Ephemerides for the Galileo Project JPL Interoffice Memorandum 314 6 1261 JPL Ephemeris References Jacobson et al 1989 Lieske 1995 Jacobson 1994 Jacobson 1991 Jacobson Jacobson Jacobson Jacobson Jacobson Laskar amp Jacobson Jacobson 1987 1996b Jacobson Jacobson Owen et al et al 1991 et al 1991 1991 Tholen 1990 10 11 12 internal document Jacobson R A 1994 Revised Ephemerides for the Inner Jovian Satellites JPL Interoffice Memorandum 314 10 101 JPL internal document Jacobson R A 1995 The Orbits of the Minor Saturnian Satellites Bulletin American Astronomical Society vol 27 No 3 p 1202 1203 Jacobson R A 1996a Update of the Major Saturnian Satellite Ephemerides JPL Interoffice Memorandum 312 1 96 012 JPL internal document Jacobson R A 1996b Updated Ephemerides for the Minor Uranian Satellites JPL Interoffice Memorandum 312 1 96 014 JPL internal document Jacobson R A 1996c Update of the Ephemeris for Phoebe JPL Interoffice Memorandum 312 1 96 024 JPL internal document Jacobson R A Synnott S P and Campbell J K 1989 The Orbits of the
48. lunar target body and the center of the primary body it revolves around as seen by the observer Units are ARCSECONDS Non lunar natural satellite visibility codes limb to limb t Transitting primary body disk 0 Occulted by primary body disk p Partial umbral eclipse P Occulted partial umbral eclipse u Total umbral eclipse U Occulted total umbral eclipse Target is the primary body None of above free and clear the radius of major bodies is taken to be the equatorial value max defined by the IAU2000 system Atmospheric effects and oblateness aspect are not currently considered in these computations Light time is Labels ang sep v 13 Target angular diameter The angle subtended by the disk of the target seen by the observer if it was fully illuminated The target diameter is taken to be the IAU2000 equatorial diameter Oblateness aspect is not currently included Units are ARCSECONDS Labels Ang diam 14 Obs sub long amp sub lat The planetographic geodetic longitude and latitude of the center of the target disk seen by the observer Uses the IAU2000 rotation models For the gas giants only Jupiter Saturn Uranus and Neptune these longitudes are based on the Set III prime meridian angle referred to the planet s rotating magnetic field Latitude is always referred to the body dynamical equator Note there can be an offset between the dynamical pole and the magnetic pole Units are DEGREES
49. me Abbrev Constellation Name And Andromeda Leo Leo Ant Antila LMi Leo Minor Aps Apus Lep Lepus Aqr Aquarius Lib Libra Aql Aquila Lup Lupus Ara Ara Lyn Lynx Ari Aries Lyr Lyra Aur Auriga Men Mensa Boo Bootes Mic Microscopium Cae Caelum Mon Monoceros Cam Camelopardis Mus Musca Cnc Cancer Nor Norma CVn Canes Venatici Oct Octans CMa Canis Major Oph Ophiuchus CMi Canis Minor Ori Orion Cap Capricornus Pav Pavo Car Carina Peg Pegasus Cas Cassiopeia Per Perseus Cen Centaurus Phe Phoenix Cep Cepheus Pic Pictor Cet Cetus Psc Pisces Cha Chamaeleon PsA Pisces Austrinus Cir Circinus Pup Puppis Col Columba Pyx Pyxis Com Coma Berenices Ret Reticulum CrA Corona Australis Sge Sagitta CrB Corona Borealis Sgr Sagittarius Crv Corvus Sco Scorpius Crt Crater Scl Sculptor Cru Crux Sct Scutum Cyg Cygnus Ser Serpens Del Delphinus Sex Sextans Dor Dorado Tau Taurus Dra Draco Tel Telescopium Equ Equuleus Tri Triangulum Eri Eridanus TrA Triangulum Australe For Fornax Tuc Tucana Gem Gemini UMa Ursa Major Gru Grus UMi Ursa Minor Her Hercules Vel Vela Hor Horologium Vir Virgo Hya Hydra Vol Volans Hyi Hydrus Vul Vulpecula Ind Indus Lac Lacerta SPK File Generation Introduction An SPK file is a binary file which may be smoothly interpolated to retrieve an object s position and velocity at any instant within the file time span Such files may be used as input to visualization and mission design prog
50. mes and designations Name searches consider spaces Designation searches consider spaces AND upper lower case If you want to match a fragment of a name or designation end it with a e g DES 1993 Otherwise it is assumed a complete name or designation is specified and the search must match exactly and completely For example NAME NAME CERES matches only if object name is Ceres CERES match Ceres Monoceres etc The same keyword can be used more than once in a search command For example IN gt 10 IN lt 20 will list those objects possessing an inclination between 10 and 20 degrees If the directive LIST is in the search request the matched parameters will be displayed For example IN gt 150 LIST will display the inclination of each object with inclination greater than 150 degrees Once a small body is uniquely identified a screen of data will be displayed If more than one small body matches given parameters a list of matching objects is displayed Individual objects from the matched list can then be requested by giving the displayed record number followed by a semi colon The semi colon is used to indicate a small body request and resolve number ambiguities For example if you enter 1 you will select Mercury Barycenter Enter 1 to retrieve the small body in record 1 Ceres Small body record numbers are assigned as follows Record range Object type 1 gt 100000 Reserved for NUMBERED a
51. n Line Ephemeris System provides easy access to key solar system data and flexible production of highly accurate ephemerides for solar system objects This includes 170 000 asteroids amp comets 128 natural satellites 9 planets the Sun select spacecraft and several dynamical points such as Earth Sun L1 L2 and system barycenters Users may define their own objects then use the system to integrate the trajectory or conduct parameter searches of the comet asteroid database searching on combinations of up to 42 different parameters Rise transit and set may be identified to the nearest minute Close approaches by asteroids and comets to planetary bodies and Ceres Pallas and Vesta can be easily identified Orbit uncertainties can be computed for asteroids and comets More than 100 different observational and physical aspect quantities can be requested at intervals for both topocentric and geocentric situations in one of 9 coordinate systems and 4 time scales CT TT UT Civil Over 750 Earth station locations are on file along with several on other major bodies Users may search for or define topocentric site coordinates on any planet or natural satellite with known rotational model if the desired site is not predefined Output is suitable for observers mission planners and other researchers although this determination is ultimately the users responsibility Five types of customizable output can be requested Observables RA DEC Az El p
52. n angle Satellite differential coordinates WRT the central body along with the satellite position angle Differential coordinates are defined in RA as X RA_sat RA_primary COS DEC_primary and in DEC as Y DEC_sat DEC_primary Non Lunar satellites only SatPANG is CCW angle from the North Celestial Pole to a line from planet center to satellite center Units ARCSECONDS X amp Y and DEGREES position angle Labels X_ sat primary Y SatPANG 7 Local Apparent Sidereal Time The angle measured westward in the body true equator of date plane from the meridian containing the body fixed observer to the meridian containing the true Earth equinox defined by intersection of the true Earth equator of date with the ecliptic of date For non Earth sites a somewhat different definition is used The value returned is measured from the observer meridian to the meridian containing the Earth equinox of the J2000 0 system TOPOCENTRIC ONLY Units are HH MM SS ffff or decimal hours HH ffffffffff Labels L_Ap_ Sid Time 8 Airmass Relative optical airmass a measure of extinction The ratio between the absolute optical airmass at target refracted elevation to the absolute optical airmass at zenith Based on work of Kasten and Young Applied Optics vol 28 no 22 15 Nov 1989 TOPOCENTRIC ABOVE HORIZON ONLY Unitless Labels a mass 9 Vis mag amp Surf Bright Approximate apparent visual magnitude amp surface brightness Value for Pluto in
53. nal time of closest approach Units KM SMiA 3 sigma error ellipse semi minor axis projected into the B plane at nominal time of closest approach Units KM Gamma Orientation angle of error ellipse in the B plane Counter clockwise angle from the B vector to the semi major axis of the error ellipse Units DEGREES Nsigs The number of standard deviations sigmas required for the error ellipse to intersect the body being closely approached Units STANDARD DEVIATIONS P_i p Linearized probability of the object impacting the body UNDERSTANDING RISE TRANSIT AND SET INDICATORS There are 2 ways the system can be used to mark rise transit and set RTS conditions activate the RTS only print option OR produce a general observer table with step size less than 30 minutes NORMAL_TABLE RTS MARKER MODE RTS is indicated automatically during normal observer table generation when the step size is less than 30 minutes Markers are placed to indicate the event occurred at some point in the previous step Thus precision of the indicator depends on the step size selected For this mode rise and set are always with respect to the true visual horizon reference plane TVH described below RTS ONLY PRINT MODE The advantage of this mode is it allows production of a more compact RTS table over a longer time span than does the normal table generation mode When RTS only print is selected the program will search for the events at a
54. ns these rise set times should be viewed as approximations realistically good to perhaps only 1 2 minutes at the horizon due to local atmospheric variation and topography To speed RTS only searches use the largest step size compatible with the required accuracy For example considering the inherent atmospheric instability at the horizon one should rarely need to identify rise set to better than 5 minute accuracy Setting a search step of 5 minutes will then produce a table 5 times faster than 1 minute searching The program computes approximate refraction angles assuming yellow light observations at 10 deg C sea level with pressure of 1010 millibars Corrected coordinates should be accurate to lt 10 arcsec but errors may be much larger near the horizon 0 3 deg or fluctuate unpredictably with local weather Both Moon and Sun rise set are based on when the refracted upper limb of the object reaches the specified elevation Transit is based on the center of the target body CONSTELLATION IDENTIFICATION One output value that may be requested for an observer table is the constellation it is observed to be in corrected for light time The output field will contain a three letter abbreviation of the constellation name from the list shown below Constellation boundaries are those delineated by Gould 1877 and Delporte 1930 under the auspices of the International Astronomical Union Abbrev Constellation Na
55. object with respect to any major body Reference frame gi J2000 ICRF J2000 0 B1950 FK4 B1950 0 Coordinate system Earth mean equator and equinox of frame Epoch J2000 0 or B1950 0 Ecliptic and mean equinox of frame Epoch J2000 0 or B1950 0 Central body mean equator and node of date Units KM and seconds KM and days AU and days Output quantities fixed JDCT Epoch Julian Date Coordinate Time EC Eccentricity QR Periapsis distance IN Inclination w r t xy plane degrees OM Longitude of Ascending Node degrees W Argument of Perifocus degrees Tp Periapsis time user specifies absolute or relative date N Mean motion degrees DU MA Mean anomaly degrees TA True anomaly degrees A Semi major axis AD Apoapsis distance PER Orbital Period 3 Observer table Any object with respect to geocentric or topocentric observer Default quantities Always output Time Solar presence Lunar presence Selectable quantities Output in order requested No initial default exists You will be prompted at least once A detailed definition of these values follows with the symbols marking those quantities affected by user selection of airless or refraction corrected apparent quantities Quantities preceded by a gt are statistical uncertainties that can be computed for asteroids and comets if a covariance is available either in the database or supplied by the user Numbers could change if new quantities are added Sat X
56. of component error is also shown If the error from the default mesh selection is too large for your application contact Jon D Giorgini jpl nasa gov for instructions on forcing Horizons to a tighter mesh and improving fidelity The above data along with other summary information is stored in the SPK file comment area It can be read using the spacit or commnt utility in the SPICE Toolkit distribution Transferring SPK files Within the Horizons system SPK files are created as binary files on a Sun UltraSparc UNIX platform These files can be used on several popular platforms but may be unreadable on others Reasons for this include 1 Data type representation machine word size 2 Floating point representations IEEE or not 3 Byte order least significant byte first vs last If you are using a verion of the SPICE Toolkit higher than 52 you will be able to directly read Horizons binary files on any platform If not the machine you intend to use the SPK file on thus falls into one of two possible categories Compatible systems If your system has 32 bit words IEEE floating point and is big endian stores highest order byte first like the Sun UltraSparc you will be able to use Horizons generated binary SPK files directly respond no to the transfer format prompt and use the binary mode of FTP to retrieve the file Known compatible machines are the HP 9000 series Motorola 68K series MacIntosh Silicon Graphics and N
57. of the error ellipse in the direction of increasing DEC Units DEGREES Area_3sig Area of sky enclosed by the 3 sigma error ellipse Units ARCSECONDS 2 38 Plane of sky ellipse RSS pointing uncertainty The Root Sum of Squares RSS of the 3 standard deviation plane of sky error ellipse major and minor axes This single pointing uncertainty number gives an angular distance a circular radius from the target s nominal position in the sky that encompasses the error ellipse Units ARCSECONDS Labels POS 3sigma 39 Uncertainties in plane of sky radial direction Range and range rate radial velocity formal 3 standard deviation uncertainties Units KM KM S Labels RNG_3sigma RNGRT_3sig 40 Radar uncertainties plane of sky radial direction Doppler radar uncertainties at S band 2380 MHz and X band 8560 MHz frequencies along with the round trip total delay to first order Units HERTZ and SECONDS Labels DOP_S sig DOP_X sig RT_delay sig CLOSE APPROACH TABLES For asteroids and comets a close approach table may be requested Output is produced only when the selected object reaches a minimum distance within a set spherical radius from a planet Ceres Pallas or Vesta User specifications for this table can include the time span to check the radius of detection for planets and asteroids the maximum uncertainty in time of close approach before the table is automatically cut off and whether to output optional error ellipse
58. oid Physical Parameters Radius and Albedo Tedesco E F 1995 IMPS Diameters and Albedos V1 0 Planetary Data System Small Bodies Node PDSSBN M A Hearn University of Maryland College Park Maryland http pdssbn astro umd edu McFadden L A et al 1989 In Asteroids Il p 456 Williams J G 1990 Private Communication Taxonomic Type Spectral Type 1 Tholen D J 1989 Asteroid Taxonomy V1 0 Planetary Data System Small Bodies Node PDSSBN M A Hearn University of Maryland College Park Maryland http pdssbn astro umd edu 2 Binzel R P and Xu S 1993 Science 216 186 191 Rotation Period 1 Harris A W 1996 Asteroid Lightcurve Derived Data V2 0 Planetary Data System Small Bodies Node PDSSBN M A Hearn University of Maryland College Park Maryland http pdssbn astro umd edu Magnitude Parameters 1 Minor Planet Circulars MPC published by the Minor Planet Center 60 Garden St Cambridge Massachusetts 02138 http cfa www harvard edu cfa ps mpc html Constants and Model References Major body planet satellite GM and AU definitions ACTUALLY USED as opposed to the FYI data screens are from the DE 405 ephemeris a significant improvement over the earlier DE 200 Other planet and satellite constants used by this software such as radii rotation and orientation are based on the following sources 1 Report of the IAU IAG Working Group on Cartographic Coordinates
59. poch This is due to round off error in the published coefficients and truncation to a 3rd order polynomial in the expressions for the Euler rotation angles Therefore outside this interval the long term precession and obliquity model 17 of Owen is used to maintain accuracy in the calculation of apparent of date quantities This model is a rigorous numerical integration of the equations of motion of the celestial pole using Kinoshita s model for the speed of luni solar precession NUTATION MODEL The IAU 1980 model 18 of Wahr is used This is the same table printed in the 1992 Explanatory Supplement to the Astronomical Almanac Note there is an error in the Explanatory Supplement for the Node term given on p 114 as OMEGA 135deg 2 40 280 This system uses the correct formulation OMEGA 125deg 2 40 280 UNIVERSAL TIME CT gt UT Conversion This program internally uses the CT time scale of the ephemerides the independent variable in the equations of motion To produce the more familiar Universal Time UT output tied to the Earth s rotation it is necessary to use historical reconstructions of old or ancient observations of constrained events such as eclipses to derive a CT UT difference This program currently uses the analyses of 12 15 as follows Span CT UT offset delta t Type Argument T 3000 BC to AD 948 31 TFT UT1 cent since 1820 AD 948 to AD 1620 50 6D0 67 5D0 T 22 5D0 T T UT1 cent since
60. r 24 Sun Target Observer angle Target s apparent PHASE ANGLE as seen from observer location at print time Units are DEGREES Labels S T 0O 25 Target Observer Moon or Interfering Body Illum Apparent elongation angle seen by the observer between the target body center and the center of a potential visually interfering body such as the Moon but more generally the largest body in the system except for the one the observer is on Also output is the fraction of the lunar or IB disk that is illuminated by the Sun A negative elongation angle indicates the target center is behind the interfering body The specific interfering body for an observing site is given in the output header Units are DEGREES and PERCENT Labels T O M I11u Earth observer M denoting Moon T O I 1I11u Non Earth observer 26 Observer Primary Target angle Apparent angle between a target satellite its primary s center and an observer at print time Units DEGREES Labels O P T 27 Pos Ang radius amp vel The position angles of the extended Sun gt target radius vector PsAng and the negative of the target s heliocentric velocity vector PSAMV as seen in the plane of sky of the observer measured CCW from reference frame North Celestial Pole Small bodies only Units are DEGREES Labels PsAng PsAMV 28 Orbit Plane Angle Angle between observer and target orbital plane measured from center of target at the moment light seen at observat
61. rams allowing them to quickly retrieve accurate target body observation and data analysis ephemerides without having to repeatedly integrate equations of motion An SPK file could be considered a recording of the integrator SPK stands for Spacecraft and Planet Kernel It is a file element of the SPICE system devised and maintained by the NAIF Navigational and Ancillary Information Facility team at JPL SPK files may hold ephemerides for any kind of spacecraft vehicle or solar system body but the SPK files produced by Horizons are only for comets and asteroids Potential users are advised that programming and science math skills at an advanced college level are needed to utilize these files Users must have a computer with 25 50 Mbytes of disk space 8 Mbytes of available RAM and a FORTRAN or C compiler The user s own code must be capable of calling FORTRAN or C modules Internet FTP capability is needed to obtain the necessary SPICE components as well as the SPK files generated by Horizons For information on SPK files in general contact Charles H Acton Jr jpl nasa gov NAIF Team Leader or see web site http pds naif jpl nasa gov Horizons Implementation IMPORTANT These informal file releases should not be used for category A flight project purposes involving the safety and success of spacecraft hardware and mission without first contacting Donald K Yeomans jpl nasa gov Supervisor Solar System Dynamics Group 818 3
62. riel 705 Miran 709 Cress 713 Rosal 717 Sycor 721 1999 008 Neptune b 899 Neptu 801 Trito 805 Despi 009 Pluto bar 999 Pluto 901 Charo s 402 Deimos arycenter er 502 Europa 503 hea 506 Himalia 507 e 510 Lysithea 511 514 Thebe 515 rycenter n 602 Enceladus 603 606 Titan 607 e 610 Janus 611 to 614 Calypso 615 ra 618 Pan rycenter s 702 Umbriel 703 da 706 Cordelia 707 ida 710 Desdemona 711 ind 714 Belinda 715 ax 718 1986U10 719 U3 arycenter ne n 802 Nereid 803 na 806 Galatea 807 ycenter n Ganymede 504 Callisto Elara 508 Pasiphae Carme 512 Ananke Adrastea 516 Metis Tethys 604 Dione Hyperion 608 Iapetus Epimetheus 612 Helene Atlas 616 Prometheus Titania 704 Oberon Ophelia 708 Bianca Juliet 712 Portia Puck 716 Caliban 1999U1 720 1999U2 Naiad 804 Thalassa Larissa 808 Proteus SOURCES AND REFERENCES FOR PRIMARY EPHEMERIS DATA Planets Standish E M XX Newhall J G Williams and W M Folkner JPL Planetary and Lunar Ephemerides DE403 LE403 JPL Interoffice Memorandum 314 10 127 dated May 22 1995 Natural Satellites Satellite Phobos amp Deimos Galileans Minor Jovians Outer Jovians Major Saturnians Phoebe Inner Saturnians Saturn co orbiters Saturn librators Major Uranians Minor Uranians Triton Nereid Inner Neptunians Charon MARSAT Analytic GALSAT E5 Analytic Precessing ellipse Numerical Integration Numerical Integration Numerical Integration Precessing e
63. s assumed to be AD Exceptions are AD years less than 100 which must have an AD symbol in the date in order to be recognized as a valid year For example 66ad jan 27 will be accepted but 66 Jan 27 cannot be parsed In this system there are no negative years The progression is as follows Julian Day Number LabelLing convention Jan 1 00 00 BC AD Arithmetical 1720327 5 3bc 2 1720692 5 2bc 1 1721057 5 1bc 0 1721423 5 lad 1 1721788 5 2ad 2 From this one can see that no days in the arithmetical year 0 for example are skipped in the BC AD scheme but they do have a different label than in the corresponding arithmetical system Output observer table lines begin with a b in column 1 to indicate B C dates and a space to indicate A D dates OUTPUT STEPPING Fixed time steps Output time steps are specified as integers with some associated units from the set days hours minutes Example responses to the prompt include 30 days 1 day 10 min and so on To get half day steps specify 12 hour It is possible to obtain output at less than 1 minute intervals telnet amp e mail interfaces only After specifying a start and stop time give a positive integer as the time step without giving units such as 10 This will divide the time span into 10 parts For example if start and stop times are one hour 3600 seconds apart specifying a step of 240 will produce output every 15 seconds 3600 15 240 intervals
64. s may also be in local civil time When specifying start time enter your time zone correction in the format YYYY Mon Dy HH MM UT s HH MM where s optional sign or If unspecified it is assumed HH integer hours time zone difference from UT MM optional minutes offset usually 0 North American standard time winter zone corrections are as follows Atlantic Standard Time AST UT 4 hours Eastern Standard Time EST UT 5 hours Central Standard Time CST UT 6 hours Mountain Standard Time MST UT 7 hours Pacific Standard Time PST UT 8 hours If daylight savings is in effect summer add one hour to above offsets For example 1999 jun 2 12 30 UT 8 produces a table in Pacific Standard Time A 7 would provide Pacific Daylight Time or MST if it is winter GREGORIAN AND JULIAN CALENDAR DATES Input calendar dates 1582 Oct 15 and after are taken to be expressed in the extended Gregorian calendar system Prior dates are assumed to be in the Julian proleptic calendar Historically not all regions switched calendars at the same time or even in the same century Thus the user must be aware of which calendar was in effect for a particular historical record It should NOT be assumed this system s calendar automatically correlates with a date from an arbitrary historical document Here is the progression near the calendar switch point Calendar Type Calendar Date Julian Day Number Ju
65. s necessary to determine the rotation from the Earth fixed reference frame to an inertial reference frame The EOP file provides data from 1962 to the present with predictions about 78 days into the future from the date of file release For times outside the available interval Horizons uses the last value available in the file as constants For CT UT calculations it switches to the different models described above Because EOP values are fit to data it is possible an ephemeris may differ slightly from one produced days or weeks or months later especially if the original ephemeris extended into the predicted region of the EOP file The most recent ephemeris will be more accurate but if it is necessary to reproduce results exactly contact JPL EOP files are archived and the one used in your initial run indicated in your output can be retrieved Generally any numeric change will be very small and almost always negligible in a practical sense BODY ROTATIONS The modern 2000 IAU rotational models for the planets and satellites are simply extended in time as necessary BACKGROUND e Comet and asteroid orbits are INTEGRATED from initial conditions stored in the JPL maintained DASTCOM database e Planet and satellite ephemerides are INTERPOLATED from files previously generated by JPL such as the DE 405 or higher planetary ephemeris e SMALL BODY DATA SCREENS are from the JPL DASTCOM database These display constants ARE ACTUALLY USED to
66. satellites Relativity is included in observables via 2nd order terms in stellar aberration and the deflection of light due to gravity fields of the Sun and Earth for topocentric observers Deflections due to other gravity fields can potentially have an effect at the 10 4 arcsec level but are not currently included here Satellites of other planets such as Jupiter could experience deflections at the 10 3 arcsec level as well Light time iterations are Newtonian This affects light time convergence at the millisecond level position at 10 6 arcsec level For many small natural satellites the orbit orientation is well known but the position of the body along the ellipse is not Errors may be significant especially for the lesser satellites of outer planets Satellite osculating elements output by Horizons should NOT be used to initialize a separate integration or extrapolation Such elements assume Keplerian motion two point masses etc which does not match for example kinematic models such as a precessing ellipse used for some satellites One would do better extrapolating mean orbital elements at http ssd jpl nasa gov sat_elem html IF YOUR CAREER OR SPACECRAFT DEPENDS ON A NON LUNAR NATURAL SATELLITE OR SMALL BODY EPHEMERIS CONTACT JPL BEFORE USING IT YOU MUST HAVE ADDITIONAL INFORMATION TO CORRECTLY UNDERSTAND EPHEMERIS LIMITATIONS AND UNCERTAINTIES LONG TERM EPHEMERIS SOLAR SYSTEM MODEL The JPL DE 406 LE 406 extende
67. sorption is assumed so scale value to account for reflectivity For example if 15 of light is reflected specify a value for AMRAT in which the actual value is multiplied by 1 15 For asteroids additional OPTIONAL parameters can be given HY Saas Absolute magnitude parameter asteroid Gaern asasin Magnitude slope parameter can be lt 0 asteroid For comets additional OPTIONAL parameters can be given BE ee tae ss Total absolute magnitude comet M24 uranni Nuclear absolute magnitude comet KE eire Total magnitude scaling factor comet K2 Sawa ad Nuclear magnitude scaling factor comet PHCOF Phase coefficient for k2 5 comet AL Siae Radial non grav accel comet AU DAY 2 A2 ea oaea Transverse non grav accel comet AU DAY 2 AIO eg Normal non grav accel comet AU d 2 DW akses Non grav lag delay parameter comet days You may enter each value on a separate line or several on one line If you make a mistake re entering the label on another line will over ride the previously specified value To erase a value enter something like H where no value is given To cancel all input enter as the first character on a line To log out enter a q or x as first character on a line When done after having pressed lt return gt on a blank line you will be asked whether the reference frame of the elements is FK5 J2000 0 or FK4 B1950 0 You will also be asked the object name Example input EPOCH 2450200
68. st WW Il latitude of the target s apparent position corrected for light time stellar aberration precession nutation and the deflection of light due to the Sun and the most massive body in the planet s system Units DEGREES Labels GlxLat 34 Local Apparent Solar Time Local Apparent SOLAR Time at observing site TOPOCENTRIC ONLY Units are HH fffffffffff decimal hours or HH MM SS ffff 35 Earth to Site Light time Instantaneous light time of the station with respect to Earth center at print time The geometric or true separation of site and Earth center divided by the speed of light Units MINUTES Labels 399 _ins_LT 36 Plane of sky RA and DEC pointing uncertainty Uncertainty in Right Ascension and Declination Output values are the formal 3 standard deviations sigmas around nominal position Units ARCSECONDS Labels RA_3sigma DEC_3sigma 37 Plane of sky error ellipse Plane of sky POS error ellipse data These quantities summarize the target s 3 dimensional 3 standard deviation formal uncertainty volume projected into a reference plane perpendicular to the observer s line of sight Labels SMAA_3sig Angular width of the 3 sigma error ellipse semi major axis in POS Units ARCSECONDS SMIA_3sig Angular width of the 3 sigma error ellipse semi minor axis in POS Units ARCSECONDS Theta Orientation angle of the error ellipse in POS the clockwise angle from the direction of increasing RA to the semi major axis
69. steroids record asteroid 100001 gt 400000 Reserved for UNNUMBERED asteroids 400001 gt 500000 Reserved for COMET APPARITIONS Elements for more than one comet apparition may be listed apparition refers to a particular perihelion passage since out gassing near perihelion can alter the orbit for each passage Select an apparition from the list with the closest epoch prior to the date of interest for the ephemeris The record or file number of unnumbered asteroids and comet apparitions should NOT be considered constants they may change as the database is updated To enter your own heliocentric ecliptic elements type This capability is described in more detail in a later section COORDINATE CENTER OBSERVING SITE SELECTION While osculating element tables may be generated with respect to a major body center only vector and observer tables may produce output with respect to an arbitrary observing site defined with respect to a major body center EARTH SITES For the Earth a list of 750 sites is predefined The list generally matches that of the Minor Planet Center expanding on radar sites which have negative ID numbers on this system as necessary Station 500 is the geocenter NON EARTH SITES For non Earth major bodies station 500 also represents the body center For those major bodies with IAU rotational models additional topocentric sites may be defined Spacecraft landing sites are typically predefined
70. ter criteria are added Users can input their own objects as described in the next section The database is updated hourly with new objects and orbit solutions USER SPECIFIED SMALL BODIES It is possible to define an object not in the database by inputting its HELIOCENTRIC ECLIPTIC elements and some other parameters Type at the main prompt It is also possible to display a DASTCOM3 object then cut and paste elements back into the program varying parameters such as magnitude as needed Cut and paste is a function of your local terminal capability PRESS lt return gt ON A BLANK LINE WHEN DONE Input format is LABEL VALUE LABEL VALUE LABEL VALUE where acceptable label strings are defined as follows EPOCH Julian ephemeris date CT of osculating elements ECG ae Eccentricity oj a eee Perihelion distance in AU TEP sore Senos Perihelion Julian date OMe mate cers Longitude of ascending node DEGREES wrt ecliptic Wee ceosistpe cede Argument of perihelion DEGREES wrt ecliptic IN sacra os Inclination DEGREES wrt ecliptic Instead of TP QR MA A or MA N may be specified not both ee ere ee Mean anomaly DEGREES Bee ogee geen Semi major axis AU Moen es Mean motion DEG DAY Note that if you specify elements with MA TP QR will be computed from them The program always uses TP and QR OPTIONAL INPUTS RAD Object radius KM AMRAT Area to mass ratio m42 kg Total ab
71. user specified resolution from 1 to 9 minutes Output will be generated ONLY for these three events The marker symbols in the table indicate that the event took place sometime in the previous step interval This RTS only mode can be turned on at two different points in the program 1 Preferably when specifying the ephemeris search step size 2 but also in the change defaults prompt structure Three types of criteria are available for the rise and set conditions relative to an input elevation angle nominally 0 degrees Select by specifying when prompted at 1 or 2 one of these symbols TVH True visual horizon plane The horizon seen by an observer on the reference ellipsoid Allows for horizon dip effect and refraction but not local topography GEO Geometric horizon plane The horizon is defined by the plane perpendicular to the reference ellipsoid local zenith no horizon dip Refraction is allowed for RAD Radar case Geometric horizon plane no refraction For example when prompted for the step size one could enter 5 min GEO to search at five minute steps for the refracted rise set relative to the geometric horizon BACKGROUND DESCRIPTION Rise and set elevations are taken to be the maximum of 0 or the input elevation cut off value 0 90 deg set in the change defaults prompt section Thus if there are local hills one could set the cut off at 10 degrees and get RTS relative to that elevation At low elevatio
72. viation statistical orbit uncertainty quantities There is a 99 7 chance the actual value is within given bounds These statistical calculations assume observational data errors are random If there are systematic biases such as timing reduction or star catalog errors results can be optimistic Because the epoch covariance is mapped using linearized variational partial derivatives results can also be optimistic for times far from the solution epoch particularly for objects having close planetary encounters NOTE n a is output if a requested quantity is not available for selected object For example azimuth and elevation for a geocentric ephemeris or uncertainties for an object with no covariance in the database SPECIFIC QUANTITIES 1 Astrometric RA amp DEC Corrected for light time only With respect to the Earth mean equator and equniox of the reference Epoch If FK4 B1950 0 frame output is selected elliptic aberration terms are added Labels R A _ ICRF J2000 0 DEC HMS DMS format R A _ FK4 B1950 0 DEC HMS DMS format R A _ J2000 0 DEC degree format R A _ B1950 0 _DEC degree format 2 Apparent RA amp DEC Apparent right ascension and declination of the target with respect to the center site body s true equator and Earth equinox of date For non Earth sites with rotational models the origin of RA is the meridian containing the Earth equinox of J2000 0 For non Earth sites without rotational models RA and DEC are
73. ward or counter clockwise as seen from the north pole For such bodies east longitude is measured negatively to the east 0 to 360 degrees from the prime meridian Retrograde rotation is rotation clockwise westward as seen from the north pole East longitude is measured positively to the east 0 to 360 degrees from the prime meridian Exceptions are the Earth Moon and Sun where longitude has historically been measured both east and west of the prime meridian 0 to 180 degrees Though these bodies are direct rotators longitude is nonetheless measured positively to the east on this system 0 to 360 degrees due to historical precedence If the positive west longitude of a site on these 3 bodies is given it should be input here as positive east longitude which would be 360 West Longitude If the negative east longitude is given instead for these exceptions only one can input the negative east longitude It will be converted to a positive east longitude on output however The following major bodies are either retrograde or exceptions and require site input with positive east longitude Retrograde east longitude Venus 299 Arial 701 Umbriel 702 Titania 703 Oberon 704 Miranda 705 Cordelia 706 Ophelia 707 Bianca 708 Cressida 709 Desdemona 710 Juliet 711 Portia 712 Rosalind 713 Belinda 714 Puck 715 Uranus 799 Pluto 999 Charon 901 Also east longitude prograde exceptions Sun
74. with respect to the REFERENCE FRAME FK4 B1950 or ICRF J2000 0 coordinate system Corrected for light time the gravitational deflection of light stellar aberration precession and nutation There is an optional approximate correction for atmospheric refraction Earth only Labels R A _ a apparent DEC airless HMS DMS format R A _ r apparent DEC refracted HMS DMS format R A _ a appar DEC airless degrees format R A _ r appar _ DEC refracted degrees format 3 Rates RA amp DEC The rate of change of apparent RA and DEC airless d RA dt is multiplied by the cosine of declination Units are ARCSECONDS PER HOUR Labels dRA cosD d DEC dt 4 Apparent AZ amp EL Apparent azimuth and elevation of target Corrected for light time the gravitational deflection of light stellar aberration precession and nutation There is an optional approximate correction for atmospheric refraction Earth only Azimuth measured North 0 gt East 90 gt South 180 gt West 270 Elevation is with respect to plane perpendicular to local zenith direction TOPOCENTRIC ONLY Units DEGREES Labels Azi_ a appr _ Elev airless Azi_ r appr Elev refracted 5 Rates AZ amp EL The rate of change of target apparent azimuth and elevation airless d AZ dt is multiplied by the cosine of the elevation angle TOPOCENTRIC ONLY Units are ARCSECONDS PER MINUTE Labels dAZ cosE d ELV dt 6 X amp Y satellite offset amp positio
75. y Ideally macro names would be something clean and logical OBS670 1 for macro 1 for Observatory Code 670 etc but the name is up to you The use of macros may make it less likely to stumble upon new capabilities as they are added though they will described here and in the system news as appropriate INTEGRATOR DISPLAY Comet and asteroid ephemerides are integrated from initial conditions called osculating elements These describe the 3 dimensional position and velocity of the body at a specific time The integrator starts with this state and takes small time steps summing the perturbing forces at each step before taking another step A variable order variable step size integrator is used to control error growth In this way the gravitational attraction of other major solar system bodies on the target body trajectory is taken into account The integrator starts at the epoch or time of the osculating elements It then integrates forward or backward as necessary to the start of the requested table Once it reaches the table start time it may have to reverse direction and go forward in time to generate the table Every 50th step will be displayed so the user can get some sense of the progress of the ephemeris Direction reversals are also displayed If output is requested at small time intervals the integrator may proceed rapidly to the start of the table There may then be long apparent pauses as numerous interpolat

HORIZONS User Manual Version 3.12 (January 4, 2005)

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