DATE Universal time (UT) of date. Time given is either 0h UT or the time
of the night that is most favorable for observing the Comet. This may
convert to the date before/after in your local time zone. If the
comet is moving rapidly then some interpolation of the tabular values
may be needed when observing at various times during the night.
DEC,RA Declination and Right Ascension: Epoch 1950 or 2000.
DELTA,R Comet-Earth and Comet-Sun distances in astronomical units (au).
MAG Magnitude (brightness)
MAGS Magnitude with scattering angle correction. This helps show any enhancement
in brightness from forward scattering.
PHA Phase angle. Values between 50-130 degrees indicate a gas tail
foreshortening of less than 25%. In the event of a close approach
to the earth, this is also the maximum possible angular tail length
of a very long straight gas tail pointing in the anti-solar direction.
Values over 90 degrees indicate forward scattering could enhance the
dust component of the comet's brighteness.
PLANE Angle the Comet-Earth line makes with the plane of the Comet's orbit and dust tail.
An angle of zero means the dust tail is viewed edge on; 90 deg is face on.
TAIL (Gas) tail length in degrees assuming actual length according to
Andreas Kammerer's formula (originally from ICQ 16, pp. 144-148,
Oct. 1994, updated by personal communication Mar. 1996).
TPA Position Angle towards which the gas tail should point (assuming it
points directly away from the sun). This can be used to estimate the
PA of the line connecting the sun and comet to help find comets in
bright twilight or daylight. It also gives an estimate of the best
latitude on earth to see the comet. For an evening comet this would
be approximately 90-TPA. For a morning comet it would be TPA-270.
TLAU (Gas) tail length in AU according to the calculations in 'TAIL'.
ALDF Comet minus Sun altitude when Comet is 3 Deg above horizon.
Useful for bright comets embedded in twilight.
AZDF Comet minus Sun azimuth when Comet is 3 Deg above horizon
RISE Rise Time (LST - Local Standard Time). The time zone relative to
UTC is given in hours after the site longitude on each page header.
Typically for Daylight Savings Time an additional hour should be added.
TRAN Transit Time (LST) - comet on the meridian, often the best viewing time.
SET Set Time (LST)
Note that the RISE, TRAN, and SET times listed will change if you are
at a different longitude within your time zone than the longitude
(listed at the top) for which the ephemeris is calculated.
Note that RISE, TRAN, and SET times are valid at the listed UT that
was selected by the program for the daily report. These may have to
be interpolated to the actual UT of the RISE, TRAN, and SET to obtain
more accurate values, particularly if the comet is near to the sun
or to the earth.
A refraction of 34 arcminutes is assumed for the RISE and SET times.
TWI Best time to watch (LST) if twilight is a limiting factor in comet
visibility. "R/S" respectively denotes morning/evening object with the
best viewing time at the start/end of practical twilight, here using
a solar depression angle of -16 degrees. "T" means observing is best
while twilight is in progress as in cases where the comet is very low.
MOON Moonrise or moonset time (LST) if moon interferes in Comet's visibility.
Moon is considered bright when EMC < 1.8 X (EMS - 40)
OR EMC < 6.0 X (EMS - 60).
"R"/"S" denotes MOON Rise/Set, "T" denotes that due to the moon's
interference, the best viewing may be at the "opposite" twilight from
what one would expect if the moon were not a factor.
BEST ---------- BEST time for viewing Comet (LST) ----------------
As a first approximation this is the TRAN time.
This is superseded by the TWI time (if given).
The first two are superseded by the MOON time (if given).
The BEST time is generally consistent with the fractional UTC Date.
AL1 Altitude (elevation angle) of Comet at best time for viewing taking
twilight into account. This may be either in a dark sky or during twilight.
AL2 Altitude of Comet at best time for viewing taking twilight and moonlight
into account.
AZ1 Azimuth of Comet at best time for viewing taking twilight into account.
AZ2 Azimuth of Comet at best time for viewing taking twilight and moonlight
into account (given when comet's visibility is strongly hampered by
moonlight).
EMS Elongation of the moon from the sun (corresponds to moon's phase).
EMC Elongation of the moon from the Comet.
MGLM Limiting magnitude of the sky locally in the vicinity of the comet. If
the comet magnitude is brighter than this it should be visible by
naked eye. The faintest the local limiting magnitude can be equal to
the "Naked Eye Limiting Magnitude" in the heading, based on the site's
light pollution.
VIS Effective magnitude of the comet, corrected for sky conditions such as
extinction, twilight, moonlight, and daylight. If less than the "Naked
Eye Limiting Magnitude" the comet should be visible naked eye. If less
than about 8.0 it should be visible in binoculars. This is accompanied
by 'N' if it is a nighttime dark sky comet or 'T' if best while twilight
is in progress. 'M' means noticeably hampered by moonlight. 'O' means
best viewing happens when the moon rises or sets. 'D' denotes best
potential for viewing is in the daytime. A blank '-' character means
essentially invisible.
Ephemeris calculated by Steve Albers, using software I developed from scratch and refined over the years.
Orbital Elements are generally from the JPL Horizons or Seiichi Yoshida's page.