NASA Horizons output quantitities description
by Luca Cassioli 21019
Original NASA description: link
NASA Horizons unofficial Graphic User Interface: link

Extended name	Unit	Column name	Full description	Picture
TIME		Date__(UT)__HR:MN	TIME
Solar presence		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
Lunar presence		Lunar presence	The solar-presence symbol is immediately followed by a lunar-presence symbol: 'm' Refracted upper-limb of Moon on or above apparent horizon ' ' Refracted upper-limb of Moon below apparent horizon OR geocentric ephemeris
1. Astrometric RA and Dec	HH MM SS.ffff	R.A._(ICRF/J2000.0)	Astrometric() right ascension and declination* of the target with respect to the specified observing center/site, epressed with respect to the planetary ephemeris ICRF/J2000 equator and equinox (i.e. for equator and equinox calculated for date J2000). Compensated for light travel time only. (*) Not depending on features of body where observer is located.
1. Astrometric RA and Dec	HH MM SS.ffff	DEC_(ICRF/J2000.0)
*2. Apparent RA and Dec	HH MM SS.ffff	R.A._(a-app)	Airless apparent() right ascension and declination* of the target center with respect to specified observing center/site. Corrections and reference system vary depending on body where observing site is located: Earth: Reference system: Type: 3d/spherical Fundamental plane: Parallel to Earth equator for current date Center: Earth center Start point: Earth equinox for current date Corrections: light-time delay gravitational deflection of light stellar aberration atmospheric refraction precession nutation other motion of the spin-pole Body w/o rotational model: Reference system: ICRF/J2000 Type: 3d/spherical Fundamental plane: Parallel to Sun equator, i.e. ecliptic Center: Sun center Start point: Earth equinox Corrections: light-time delay gravitational deflection of light stellar aberration (no atmospheric refraction) (no precession) (no nutation) Body with rotational model: Reference system: Type: 3d/spherical Fundamental plane: through equator of the body Center: Body center Start point: Earth equinox Corrections: light-time gravitational deflection of light stellar aberration (no atmospheric refraction) (usually no precession) (usually no nutation) (*) Corrected as per above-lised quantities. Reference 1 Reference 2
*2. Apparent RA and Dec	HH MM SS.ffff	DEC_(a-app)
3. Rates; RA and Dec	ARCSECONDS PER HOUR	dRA*cosD	The rate of change of target center apparent RA and DEC (airless). d(RA)/dt is multiplied by the cosine of the declination. Reference system: Type: 3d/spherical Fundamental plane: Parallel to Earth equator for current date Center: Earth center Start point: Earth equinox for current date
3. Rates; RA and Dec	ARCSECONDS PER HOUR	d(DEC)/dt
*4. Apparent Az and Elev	DEGREES	Azi_(a-app)	Airless apparent azimuth and elevation of target center. Adjusted for light-time, the gravitational deflection of light, stellar aberration, precession and nutation. Azimuth measured North(0) -> East(90) -> South(180) -> West(270) -> North (360). Elevation is with respect to plane perpendicular to local zenith direction. Topocentric only
*4. Apparent Az and Elev	DEGREES	Elev_(a-app)
5. Rates; AZ and El	ARCSECOND/MINUTE	dAZ*cosE	The rate of change of target center apparent azimuth and elevation (airless). d(AZ)/dt is multiplied by the cosine of the elevation angle. Topocentric only
5. Rates; AZ and El	ARCSECOND/MINUTE	d(ELV)/dt
6. X & Y satellite coordinates & position angle	ARCSECONDS	X_(sat-prim)	Satellite differential() X coordinate* WRT the primary body. X=[(RA_sat - RA_primary)COS(DEC_primary)] Non-Lunar satellites only. ()Differences between angles on the celestial sphere	(Click for detailed explanation)
		Y_(sat-prim)	Satellite differential Y coordinate WRT the primary body. Y=(DEC_sat-DEC_primary). Non-Lunar satellites only. (*)Differences between angles on the celestial sphere	(Click for detailed explanation)
		SatPANG	Satellite position angle in celestial sphere. Angle start: line joining primary-body center to North Celestial Pole Angle end: line joining primary-body center to target center (=satellite orbiting the primary body) Direction: counter-clockwise (CCW, or east)
7. Local apparent sidereal time	HH MM SS.ffff	L_Ap_Sid_Time	Local Apparent Sidereal Time Angle measured over the plane of "true-equator of-date" of the body. Angle start: Meridian containing the observer on the center-body. Angle end: meridian containing the true Earth equinox (defined by intersection of the true Earth equator of date with the ecliptic of date). Direction: Westward Topocentric only.
8. Airmass	None (airmass) and magnitudes (extinction)	a-mass	Available only for topocentric Earth sites when the target is above the horizon. Relative optical airmass and visual magnitude extinction. Airmass is the ratio between the absolute optical airmass for the target's refracted CENTER point to the absolute optical airmass at zenith. Also output is the estimated visual magnitude extinction due to the atmosphere, as seen by the observer.
9. Visible magnitude and surface brightness	magnitudes	mag_ex	Target's approximate apparent visual magnitude & surface brightness. For planets and satellites, values are available only for solar phase angles in the range generally visible from Earth. This is to avoid extrapolation of models beyond their valid (data-based) limits.
	MAGNITUDE	APmag
	VISUAL MAGNITUDES PER SQUARE ARCSECOND	S-brt
10. Illuminated fraction	PERCENT	Illu%	Fraction of target circular disk illuminated by Sun (phase), as seen by observer (=quantity 25). For value of phase angle see quantities 24 and 43
11. Defect of illumination	ARCSECONDS	Def_illu	Defect of illumination. Maximum angular width of target circular disk diameter not illuminated by the Sun.
12. Satellite angle separation/visibility	ARCSECONDS	ang-sep	Target-primary angular separation. Angle start: line joining observer to target (satellite) Angle end: line joining observer to primary body around which the satellite is orbiting Direction: not used
12. Satellite angle separation/visibility	Non-lunar natural satellite visibility codes (limb-to-limb)	v	Target visibility w.r.t its primary body (i.e. eclipses/occultations). Possible values: /t = Transitting primary body disk /O = 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")
13. Target angular diam.	ARCSECONDS	Ang-diam	The equatorial angular width of the target body full disk, if it were fully visible to the observer.
14. Observer sub-longitude and sub-latitude	DEGREES	Ob-lon	Apparent planetodetic longitude and latitude (IAU2009 model) of the center of the target disk seen by the observer at print-time. For a non-spherical target shape, this is not exactly the same as the "sub-observer" (nearest) point , but if not an irregular body shape, it is generally very close. Down-leg light travel-time from target to observer is taken into account. Latitude is the angle between the equatorial plane and the line perpendicular to the reference ellipsoid of the body. The reference ellipsoid is an oblate spheroid with a single flatness coefficient in which the y-axis body radius is taken to be the same value as the x-axis radius. For the gas giants Jupiter, Saturn, Uranus and Neptune, IAU2009 longitude is based on the "System 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. Positive longitude is to the EAST.
14. Observer sub-longitude and sub-latitude	DEGREES	Ob-lat
15. Sun sub-longitude and sub-latitude	DEGREES	Sl-lon	Apparent planetodetic longitude and latitude of the Sun (IAU2009) as seen by the observer at print-time. For a non-spherical target shape, this is not exactly the same as the "sub-solar" (nearest) point , but if not an irregular body shape, it is generally very close. Light travel-time from Sun to target and from target to observer is taken into account. Latitude is the angle between the equatorial plane and the line perpendicular to the reference ellipsoid of the body. The reference ellipsoid is an oblate spheroid with a single flatness coefficient in which the y-axis body radius is taken to be the same value as the x-axis radius. For the gas giants Jupiter, Saturn, Uranus and Neptune, IAU2009 longitude is based on the "System 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. Positive longitude is to the EAST.
15. Sun sub-longitude and sub-latitude	DEGREES	Sl-lat
16. Sub Sun Position Angle and Distance	DEGREES	SN.ang	Target sub-solar point position angle (CCW, or east, with respect to the direction of the true-of-date Celestial North Pole)
16. Sub Sun Position Angle and Distance	ARCSECONDS	SN.dist	Target sub-solar point 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.
17. North Pole Position Angle and Distance	DEGREES	NP.ang	Target's North pole position angle (CCW, or east, with respect to direction of true-of-date Celestial North Pole) at observation time.
17. North Pole Position Angle and Distance	ARCSECONDS	NP.dist	Target's North pole angular distance from the sub-observer point (center of disk) at observation time. Negative distance indicates the planet's North pole is on the hidden hemisphere.
18. Helio eclip. longitude and latitude	DEGREES	hEcl-Lon	Geometric heliocentric J2000 ecliptic longitude and latitude of target center at the instant light leaves it to be observed at print time (print time minus 1-way light-time).
18. Helio eclip. longitude and latitude	DEGREES	hEcl-Lat
19. Helio range and rng rate	AU	r	Heliocentric range ("r", light-time-corrected) of the target center at the instant light seen by the observer at print-time would have left the target center (print-time minus down-leg light-time). The Sun-to-target distance traveled by a ray of light emanating from the center of the Sun that reaches the target center point at some instant and is recordable by the observer one down-leg light-time later at print-time.
20. Obsrv range and rng rate	AU	delta	Observer-centric range ("delta") of the target center at the instant light seen by the observer at print-time would have left the target center (print-time minus down-leg light-time); the target-to-observer distance traveled by a light ray emanating from the center of the target and recorded by the observer at print-time.
21. One-Way Light-Time	MINUTES	1-way_LT	1-way down-leg light-time from target center to observer. The elapsed time since light (observed at print-time) would have left or reflected off a point at the center of the target.
22. Speed wrt Sun and observer	KM/S	VmagSn	Heliocentric magnitude of target center velocity at the time light left the target center to be observed (print time minus 1-way light-time). These are absolute values of the velocity vectors (total speeds) and do not indicate direction of motion.
22. Speed wrt Sun and observer	KM/S	VmagOb	Observer-centric magnitude of target center velocity at the time light left the target center to be observed (print time minus 1-way light-time). These are absolute values of the velocity vectors (total speeds) and do not indicate direction of motion.
23. Sun-Observer-Target ELONG angle	DEGREES	S-O-T	Sun-Observer-Target angle; target's apparent SOLAR ELONGATION seen from the observer location at print-time. The '/r' column indicates the target's apparent position relative to the Sun in the observer's sky, as described below: Observer on rotating body (considering its rotational sense): /T = target TRAILS Sun (evening sky; rises and sets AFTER Sun) /L = target LEADS Sun (morning sky; rises and sets BEFORE Sun) Observer on not rotating body (such as a spacecraft): the "leading" and "trailing" condition is defined by the observer's heliocentric orbital motion: if continuing in the observer's current direction of heliocentric motion would encounter the target's apparent longitude first, followed by the Sun's, the target LEADS the Sun as seen by the observer. If the Sun's apparent longitude would be encountered first, followed by the target's, the target TRAILS the Sun. NOTE: The S-O-T solar elongation angle is numerically the minimum separation angle of the Sun and target in the sky in any direction. It does NOT indicate the amount of separation in the leading or trailing directions, which are defined in the equator of a spherical coordinate system.
24. Sun-Target-Observer approximate PHASE angle	DEGREES	S-T-O	"S-T-O" is the Sun->Target->Observer angle; the interior vertex angle at target center formed by a vector to the apparent center of the Sun at reflection time on the target and the apparent vector to the observer at print-time. Slightly different from true PHASE ANGLE (requestable separately as quantity "43") at the few arcsecond level in that it includes stellar aberration on the down-leg from target to observer. See also quantities 10 and 25 for illumination percentage.
25. Target-Observer-Moon/Illumination percentage	DEGREES	T-O-M	Target-Observer-Moon (or Target-Observer-InterferingBody) 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). 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. Labels: T-O-M, Illu% (Earth observer, 'M' denoting "Moon") T-O-I, Illu% (Non-Earth observer).
25. Target-Observer-Moon/Illumination percentage	%	MN_Illu%	Moon/Body illuminated percentage Fraction of the Moon (or Interfering Body) disk that is illuminated by the Sun (=quantity 10).
26. Observer-Primary-Target angle	DEGREES	O-P-T	Observer-Primary-Target angle; apparent angle between a target satellite, its primary's center and an observer, at observing location, at print time.
27. Radial and -vel posn.ang	DEGREES	PsAng	The position angles of the extended Sun->target radius vector as seen in the observer's plane-of-sky, measured CCW (east) from reference frame North Celestial Pole. Primarily intended for ACTIVE COMETS, "PsAng" is an indicator of the comet's gas-tail orientation in the sky (being in the anti-sunward direction)
27. Radial and -vel posn.ang	DEGREES	PsAMV	Negative of the target's heliocentric velocity vector, as seen in the observer's plane-of-sky, measured CCW (east) from reference frame North Celestial Pole. Primarily intended for ACTIVE COMETS, "PsAMV" is an indicator of dust-tail orientation.
28. Orbit Plane Angle	DEGREES	PlAng	Angle between observer and target orbital plane, measured from center of target at the moment light seen at observation time leaves the target. Positive values indicate observer is above the object's orbital plane, in the direction of reference frame +z axis.
29. Constellation name	text	Cnst	Constellation ID; the 3-letter abbreviation for the name of the constellation containing the target center's astrometric position, as defined by IAU (1930) boundary delineation. See documentation for list of abbreviations.
30. Delta-T (TDB - UT)	SECONDS	TDB-UT	Difference between the uniform Barycentric Dynamical time-scale and the Earth-rotation dependent Universal Time. Prior to 1962, the difference is with respect to UT1 (TDB-UT1) and the 0.002 second maximum amplitude distinction between TT and TDB is not maintained. For 1962 and later, the difference is with respect to UTC (TDB-UTC) and periodic terms less than 1.e-6 second are ignored. Values beyond the next July or January 1st may change if a leap-second is later required by the IERS. Values from the present date forward through the next ~78 days are predictions; beyond that prediction interval, the last prediction is taken as a constant for all future dates.
*31. Observer ecliptic longitude and latitude	DEGREES	ObsEcLon	Observer-centered Earth ecliptic-of-date longitude and latitude of the target center's apparent position, adjusted for light-time, the gravitational deflection of light and stellar aberration. Although centered on the observer, the values are expressed relative to coordinate basis directions defined by the Earth's true equator-plane, equinox direction, and mean ecliptic plane at print time.
*31. Observer ecliptic longitude and latitude	DEGREES	ObsEcLat
32. North pole RA and Dec	DEGREES	N.Pole-RA	ICRF/J2000.0 Right Ascension and Declination (IAU2009 rotation model) of target body's North Pole direction at the time light left the body to be observed at print time.
32. North pole RA and Dec	DEGREES	N.Pole-DC
33. Galactic latitude	DEGREES	GlxLon	Observer-centered Galactic System II (post WW II) longitude and latitude of the target center's apparent position. Adjusted for light-time, gravitational deflection of light, and stellar aberration.
33. Galactic latitude	DEGREES	GlxLat
34. Local apparent SOLAR time	HH MM SS.ffff	L_Ap_SOL_Time	Topocentric only. Local Apparent SOLAR Time for observing site. This is the time indicated by a sundial.
35. Earth -> site light-travel-time	MINUTES	399_ins_LT	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.
>36. RA and Dec uncertainty	ARCSECONDS	RA_3sigma	Uncertainty in Right-Ascension and Declination. Output values are the formal +/- 3 standard-deviations (sigmas) around nominal position.
>36. RA and Dec uncertainty	ARCSECONDS	DEC_3sigma
>37. POS error ellipse	ARCSECONDS	SMAA_3sig	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. SMAA_3sig = Angular width of the 3-sigma error ellipse semi-major axis in POS.
	ARCSECONDS	SMIA_3sig	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. SMIA_3sig = Angular width/ of the 3-sigma error ellipse semi-minor axis in POS.
	DEGREES	Theta	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. Theta = Orientation angle of the error ellipse in POS; the clockwise angle from the direction of increasing RA to the semi-major axis of the error ellipse, in the direction of increasing DEC.
	ARCSECONDS ^ 2	Area_3sig	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. Area_3sig = Area of sky enclosed by the 3-sigma error ellipse.
>38. POS uncertainty (RSS)	ARCSECONDS	POS_3sigma	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.
>39. Range and rng-rate sig.	KM	RNG_3sigma	Range +/- 3 standard-deviation formal uncertainty.
>39. Range and rng-rate sig.	KM	RNGRT_3sig	Range +/- 3 standard-deviation formal uncertainty.
>40. Doppler/delay sigmas	HERTZ	DOP_S_3sig	Doppler radar uncertainties at S-band (2380 MHz) frequency
	HERTZ	DOP_X_3sig	Doppler radar uncertainties at X-band (8560 MHz) frequency
	SECONDS	RT_delay_3sig	Doppler radar round-trip (total) delay to first-order.
41. True anomaly angle	DEGREES	Tru_Anom	Apparent true anomaly angle of the target's heliocentric orbit position; the angle in the target's instantaneous orbit plane from the orbital periapse direction to the target, measured positively in the direction of motion. The position of the target is taken to be at the moment light seen by the observer at print-time would have left the center of the object. That is, the heliocentric position of the target used to compute the true anomaly is one down-leg light-time prior to the print-time.
*42. Local apparent hour angle	HH MM SS.fff	L_Ap_Hour_Ang	Earth topocentric only Local apparent HOUR ANGLE of target at observing site. The angle between the observer's meridian plane, containing Earth's axis of-date and local zenith direction, and a great circle passing through Earth's axis-of-date and the target's direction, measured westward from the zenith meridian to target meridian along the equator. Negative values are angular times UNTIL transit. Positive values are angular times SINCE transit. Exactly 24_hrs/360_degrees.
43. PHASE angle and bisect	DEGREES	phi	"phi" is the true PHASE ANGLE at the observer's location at print time. See also 10, 24 and 25
		PAB-LON	J2000 ecliptic longitude of the phase angle bisector direction; the outward directed angle bisecting the arc created by the apparent vector from Sun to target center and the astrometric vector from observer to target center. For an otherwise uniform ellipsoid, the time when its long-axis is perpendicular to the PAB direction approximately corresponds to lightcurve maximum (or maximum brightness) of the body. PAB is discussed in Harris et al., Icarus 57, 251-258 (1984).
		PAB-LAT	J2000 ecliptic latitude of the phase angle bisector direction; the outward directed angle bisecting the arc created by the apparent vector from Sun to target center and the astrometric vector from observer to target center. For an otherwise uniform ellipsoid, the time when its long-axis is perpendicular to the PAB direction approximately corresponds to lightcurve maximum (or maximum brightness) of the body. PAB is discussed in Harris et al., Icarus 57, 251-258 (1984).

Or select a pre-defined format below:
A = All quantities B = Geocentric only C = Small-body geocentric
D = Small-body topo. E = Spacecraft geocentric F = Spacecraft topocentric

A = 1-42
B = 1-3,6,9-33,41
C = 1-3,9-11,13,18-29,33,36-41
D = 1-5,8-10,11,13,18-29,33-34,36-42
E = 1-3,8,10,18-25, 29,41
F = 1-5,8,10,18-25,29,42

*: Quantities affected by user selection of airless or refraction-corrected
apparent quantities.
>: Statistical uncertainties that can be computed and output for asteroids and
comets if a covariance is available, either in the database or supplied by
the user.

Target body: Refers to the object of interest, selected by the user. It can be a major-body or small-body.
When a surface target is specified, two new markers are placed in observer table output. They indicate if the point on the target surface is lit (by the Sun) and if it is on the near or far-side of the target body relative to the observer.

Major body

Sun
Planet
Natural satellite
Spacecraft from database
Custom spacecraft: Geocentric SGP4/SDP4 Two-Line Element (TLE) format data can be specified by users to define an Earth-orbiting artificial satellites. It is possibile to produce satellite-to-satellite ephemerides and generate relative position data for them.
(Asteroid/comet) - In special cases (such as for a spacecraft encounter), a comet or asteroid can be requested to be redefinedas a "major body".

Small body

Comet
Asteroid
Custom: It is possible to define an object not in the database by inputting its HELIOCENTRIC IAU76/J2000 ECLIPTIC elements and some other parameters.

Primary body: Closest body about which a target body orbits.

For natural satellites: their planet
For planets and small-bodies: Sun

Interfering body: Largest body in a system other than the one the observer is on, or the target. (For example, for an observer on the Earth, the "interfering body" is the Moon)

Deflecting body:Largest mass in the observer's system; used to estimate the gravitational bending (deflection) of light, in addition to that of the Sun. CENTER:
Origin of the coordinate system, or the "observing point", relative to which the ephemeris should be expressed.
For those major bodies with IAU rotational models, additional topocentric sites may be defined. Spacecraft landing sites are typically predefined on non-Earth bodies.

TLE: TWO-LINE ELEMENTS (TLEs)
Geocentric SGP4/SDP4 Two-Line Element (TLE) format data can be specified by users to define an Earth-orbiting artificial satellites.
An input TLE object can be also used as a coordinate origin (an observing point) at any time.
Once defined, a TLE object can be used in the same way as other objects available from this system.

Definitions

source

True: Both precession and nutation (time dependant)
Mean: Precession motions only (time dependant)
Of-date: Calculated in a generic date (static)
Epoch: Calculated in a fundamental reference date (e.g. J2000, 1984.0,...) (static)

SGP4 Simplified General Perturbations Satellite Orbit Model 4
TEME TRUE EQUATOR MEAN EQUINOX
TLE Two Line Element
LVLH Local Vertical Local Horizontal