TIME

Prior to 1962, times are UT1. Dates thereafter are UTC. Any "b" symbol in
the 1st-column denotes a B.C. date. First-column blank (" ") denotes an A.D.
date. Calendar dates prior to 1582-Oct-15 are in the Julian calendar system.
Later calendar dates are in the Gregorian system.

  Time tags refer to the same instant throughout the universe, regardless of
where the observer is located.

  The dynamical Coordinate Time scale is used internally. It is equivalent to
the current IAU definition of "TDB". Conversion between CT and the selected
non-uniform UT output scale has not been determined for UTC times after the
next July or January 1st.  The last known leap-second is used over any future
interval.

  NOTE: "n.a." in output means quantity "not available" at the print-time.
 
 R.A._(ICRF/J2000.0)_DEC =
   J2000.0 astrometric right ascension and declination of target center.
Adjusted for light-time. Units: HMS (HH MM SS.ff) and DMS (DD MM SS.f)
 
 R.A._(a-apparent)__DEC. =
   Airless apparent right ascension and declination of the target center with
respect to the Earth true-equator and the meridian containing the Earth true
equinox of date.  Adjusted for light-time, gravitational deflection of light,
stellar aberration, precession & nutation.
   Units: HMS (HH MM SS.ff) and DMS (DD MM SS.f)
 
 dRA*cosD d(DEC)/dt =
    The rate of change of target center apparent RA and DEC (airless).
d(RA)/dt is multiplied by the cosine of the declination.
    Units: ARCSECONDS PER HOUR
 
 Azi_(a-appr)_Elev =
   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. Units: DEGREES
 
 dAZ*cosE d(ELV)/dt =
   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. Units: ARCSECOND/MINUTE
 
 X & Y satellite coordinates & position angle =
   Satellite differential coordinates WRT the primary body along with the
satellite position angle. Differential coordinates are defined in RA as
X=[(RA_sat - RA_primary)*COS(DEC_primary)], in DEC as Y=(DEC_sat-DEC_primary).
Non-Lunar satellites only. "SatPANG" is the angle from the North Celestial
Pole measured counter-clockwise (CCW, or east) to a line from primary/planet
center to satellite center.
   Units: ARCSECONDS (X & Y) and DEGREES (position angle)
 
 L_Ap_Sid_Time =
   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).
TOPOCENTRIC ONLY. Units: HH MM SS.ffff.
 
 a-mass mag_ex=
    RELATIVE optical airmass and visual magnitude extinction. Airmass is the
ratio between the absolute optical airmass for the targets 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.
AVAILABLE ONLY FOR TOPOCENTRIC EARTH SITES WHEN THE TARGET IS ABOVE THE HORIZON
Units: None (airmass) and magnitudes (extinction).
 
 APmag S-brt =
   Suns approximate apparent visual magnitude & surface brightness.
APmag= M - 5 + 5*log10(d), where M= 4.83 and d= distance from Sun in parsecs.
   Units: MAGNITUDE & VISUAL MAGNITUDES PER SQUARE ARCSECOND
 
 Illu% =
   Fraction of target circular disk illuminated by Sun (phase), as seen by
observer.  Units: PERCENT
 
 Def_illu =
   Defect of illumination. Maximum angular width of target circular disk
diameter not illuminated by the Sun.  Units: ARCSECONDS
 
 ang-sep/v =
  Target-primary angular separation and visibility. The angle between the
center of target object and the center of the primary body it revolves around,
as seen by the observer. Units: ARCSECONDS

  Non-lunar natural satellite visibility codes (limb-to-limb):
    /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")
 
 Ang-diam =
   The equatorial angular width of the target body full disk, if it were
fully visible to the observer.  Units: ARCSECONDS
 
 Ob-lon Ob-lat =
   Apparent planetographic ("geodetic") longitude and latitude (IAU2009 model)
of the center of the target disk seen by the observer at print-time.  This is
NOT exactly the same as the "sub-observer" (nearest) point for a non-spherical
target shape, but is generally very close if not an irregular body shape.
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. Units: DEGREES
 
 Sl-lon Sl-lat =
   Apparent planetographic ("geodetic") longitude and latitude of the Sun
(IAU2009) as seen by the observer at print-time. This is NOT exactly the same
as the "sub-solar" (nearest) point for a non-spherical target shape, but is
generally very close if not an irregular body shape. 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.  Units: DEGREES
 
 SN.ang SN.ds =
  Target sub-solar point position angle (CCW, or east, with respect to the
direction of the true-of-date Celestial North Pole) and its angular distance
from the sub-observer point (center of disk) at print time. Negative distance
indicates sub-solar point on hidden hemisphere. Units: DEGREES and ARCSECONDS
 
 NP.ang NP.ds =
  Targets North pole position angle (CCW, or east, with respect to
direction of true-of-date Celestial North Pole) and its angular distance
from the sub-observer point (center of disk) at observation time.
Negative distance indicates the planets North pole is on the hidden
hemisphere.  Units: DEGREES and ARCSECONDS
 
 hEcl-Lon hEcl-Lat =
    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).  Units: DEGREES
 
 r       rdot =
   Heliocentric range ("r", light-time corrected) and range-rate ("rdot")
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.
Units: AU and KM/S
 
 delta  deldot =
   Range ("delta") and range-rate ("delta-dot") of target center with respect
to the observer 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
distance traveled by a light ray emanating from the center of the target and
recorded by the observer at print-time. "deldot" is a projection of the
velocity vector along this ray, the light-time-corrected line-of-sight from the
coordinate center, and indicates relative motion. A positive "deldot" means the
target center is moving away from the observer (coordinate center). A negative
"deldot" means the target center is moving toward the observer.
Units: AU and KM/S
 
 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. Units: MINUTES
 
 VmagSn VmagOb =
   Magnitude of target center velocity wrt Sun ("VmagSn") and the observer
("VmagOb") 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.  Units: KM/S
 
 S-O-T /r =
    Sun-Observer-Target angle; targets apparent solar elongation seen from
observer location at print-time. If negative, the target center is behind
the Sun. Angular units: DEGREES.

    The "/r" column is a Sun-relative code, output for observing sites
with defined rotation models only.

         /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.
 
 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)
at the few arcsecond level in that it includes stellar aberration on the
down-leg from target to observer.  Units: DEGREES
 
 T-O-M/Illu% =
   Target-Observer-Moon/Illuminated percentage. The apparent lunar elongation
angle between target body CENTER and the Moons CENTER, seen from the observing
site, along with fraction of the lunar disk illuminated by the Sun. A negative
lunar elongation angle indicates the target center is behind the Moon.
Units: DEGREES & PERCENT.
 
 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.
Units: DEGREES
 
 PsAng PsAMV =
   The position angles of the extended Sun->target radius vector ("PsAng")
and the negative of the targets heliocentric velocity vector ("PsAMV"),
as seen in the observers plane-of-sky, measured CCW (east) from reference
frame North Celestial Pole. Computed for small-bodies only (and primarily
intended for ACTIVE COMETS), "PsAng" is an indicator of the comets gas-tail
orientation in the sky (being in the anti-sunward direction) while "PsAMV"
is an indicator of dust-tail orientation.
   Units: 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 objects orbital plane, in
the direction of reference frame +z axis. Small-bodies only. Units: DEGREES.
 
 Cnst =
   Constellation ID; the 3-letter abbreviation for the name of the
constellation containing the target centers astrometric position,
as defined by IAU (1930) boundary delineation.  See documentation
for list of abbreviations.
 
 CT-UT =
   Difference between uniform Coordinate Time scale and 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. Units: SECONDS
 
 ObsEcLon ObsEcLat =
   Observer-centered Earth ecliptic-of-date longitude and latitude of the
target centers 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 Earths true equator-plane, equinox direction, and mean ecliptic plane at
print time.  Units: DEGREES
 
 N.Pole-RA  N.Pole-DC
    ICRF/J2000.0 Right Ascension and Declination (IAU2009 rotation model)
of target bodies North Pole direction at the time light left the body to
be observed at print time. Units: DEGREES
 
 GlxLon GlxLat =
   Observer-centered Galactic System II (post WW II) longitude and latitude
of the target centers apparent position. Adjusted for light-time,
gravitational deflection of light, and stellar aberration. Units: DEG DEG
 
 L_Ap_SOL_Time =
   Local Apparent SOLAR Time for observing site. This is the time indicated by
a sundial.  TOPOCENTRIC ONLY.  Units: HH MM SS.ffff (sexagesimal angular hours)
 
 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.  Units: MINUTES
 
 RA_3sigma DEC_3sigma =
  Uncertainty in Right-Ascension and Declination. Output values are the formal
+/- 3 standard-deviations (sigmas) around nominal position. Units: ARCSECONDS
 
 SMAA_3sig SMIA_3sig   Theta Area_3sig =
  Plane-of-sky (POS) error ellipse data. These quantities summarize the
targets 3-dimensional 3-standard-deviation formal uncertainty volume projected
into a reference plane perpendicular to the observers line-of-sight.

   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 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.
 
 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 targets nominal position in the
sky that encompasses the error-ellipse. Units: ARCSECONDS.
 
 RNG_3sigma RNGRT_3sig =
  Range and range rate (radial velocity) formal 3-standard-deviation
uncertainties.  Units: KM, KM/S
 
 DOP_S-sig  DOP_X-sig  RT_delay-sig  =
  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
 
 Tru_Anom =
   Apparent true anomaly angle of the targets heliocentric orbit position;
the angle in the targets 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. Units: DEGREES
 
 L_ap_Hour_Ang =
   Local apparent HOUR ANGLE of target at observing site. The angle between the
observers meridian plane, containing Earths axis of-date and local zenith
direction, and a great circle passing through Earths axis-of-date and the
targets 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.
EARTH TOPOCENTRIC ONLY.  Units: sHH MM SS.fff (sexagesimal angular hours)
 
   phi  PAB-LON  PAB-LAT =
   "phi" is the true PHASE ANGLE at the observers location at print time.
"PAB-LON" and "PAB-LAT" are the J2000 ecliptic longitude and 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).

   Units: DEGREES, DEGREES, DEGREES, DEGREES