Saturn Ephemeris Generator 2.3 Help
This form enables you to generate a table listing useful information
about the viewing geometry for Saturn and/or any of its moons as a
function of time. You are free to specify which of a variety of useful
quantities to tabulate. The file returned will contain a single header
line describing each column, followed by one row of numbers for each
time step.
Change History
1.0 (January 28, 1997):
Original Saturn Ephemeris Generator on line.
1.1 (February 6, 1997):
Added optional columns for sub-solar and sub-Earth inertial longitudes.
2.0 (January 12, 1999):
Added sub-solar and sub-Earth latitude/rotating longitude options.
Revised user interface.
Extended time limits and added new ephemeris option.
2.1 (January 31, 2002):
Added a new ephemeris option ("Prometheus 2002").
2.2 (January 9, 2003):
Added Phoebe. Added a new column option to provide second accuracy in time tags.
2.3 (August 8, 2007):
Added Cassini-discovered moons and the latest ephemeris options.
The start and stop times (UTC) of the table can be entered in a variety
of formats. For example, the following all parse to 0:01:02 UTC on July
4, 1976:
- 1976-JUL-04 00:01:02.00
- July 4, 1976 12:01:02 am
- 12:01:02 am July 4, 1976
- 1976-07-04T00:01:02Z (PDS format)
- MJD 42963.00071759259
- JD 2442963.50071759259
If you want the gory details of how times are interpreted, click
here.
Enter the time interval to be used for the tabulation as a number in the box,
and select the time unit from the choices provided.
Select the ephemeris you wish to use from among the choices provided.
For most purposes, the latest choice is best, but outdated ephemerides
are included to provide backward compatibility.
The model for the pole of Saturn is from French et al.
(Icarus 103, 163-214, 1993) and includes precession.
Prometheus Lag:
The first three ephemeris options do not include the 19-degree lag
to the orbit of Prometheus, discovered in 1995. As an additional option,
the correction may be applied by setting the Prometheus lag to "On".
With this option, the ephemeris uses the position of Prometheus relative
to the center of Saturn for the moment 46.3 minutes earlier than the
actual time. This option is ignored for the later ephemeris options.
Click on the box to the left of each quantity or set of quantities that
you wish to tabulate. The order of the columns in the table will match
the order listed on the form. Possible selections are as follows:
-
Modified Julian Date
Adds a column containing the Modified Julian Date, a common method
of designating dates and times in astronomy. MJD is equal to the number
of (possibly fractional) days elapsed since 0:00 UTC on 17 November
1858.
-
Year, Month, Day, Hour, Minute
Adds five columns containing the UTC date (year, month, day) and time
(hours, minutes) as integers.
-
Year, Month, Day, Hour, Minute, Second
Adds six columns containing the UTC date (year, month, day) and time
(hours, minutes, seconds) as integers.
-
Saturn RA and Dec
Adds two columns containing the J2000 right ascension and
declination of Saturn. RA is tabulated in units of hours; declinations
is in units of degrees.
-
Saturn phase angle
Adds a column containing the phase angle of Saturn as seen from
Earth, in degrees. This is equal to the Sun-Saturn-Earth angle.
-
Ring opening angle to Sun
Adds a column containing the ring plane opening angle to the Sun, in
degrees. This is equivalent to the sub-solar latitude as seen from
Saturn; it equals zero during a ring plane crossing.
-
Ring opening angle to Earth
Adds a column containing the ring plane opening angle to the Earth, in
degrees. This is equivalent to the sub-Earth latitude as seen from
Saturn; it equals zero during a ring plane crossing.
-
Sub-solar inertial longitude
Adds a column containing the sub-solar longitude at Saturn, in
degrees. This is measured from the J2000 ascending node of the planet's
equatorial plane. Note that it is an inertial longitude, not measured
in a frame rotating with the planet.
-
Sub-Earth inertial longitude
Adds a column containing the sub-Earth longitude at Saturn, in
degrees. This is measured from the J2000 ascending node of the planet's
equatorial plane. Note that it is an inertial longitude, not measured
in a frame rotating with the planet.
-
Sub-solar latitude and rotating longitude
Adds a pair of columns containing the sub-solar latitude and
longitude at Saturn, in degrees. These are measured in a frame rotating
with the planet.
-
Sub-Earth latitude and rotating longitude
Adds a pair of columns containing the sub-Earth latitude and
longitude at Saturn, in degrees. These are measured in a frame rotating
with the planet.
-
Saturn projected equatorial radius
Adds a column containing the projected equatorial radius of Saturn
as seen from Earth, in units of arcseconds.
-
Sun-Saturn distance
Adds a column containing the Sun-Saturn distance, in km.
-
Earth-Saturn distance
Adds a column containing the Earth-Saturn distance, in km.
-
Lunar phase angle
Adds a column containing the phase angle of the Moon at the
specified time, in degrees. A value near zero corresponds to a full
moon; a value near 180 corresponds to a new moon.
-
Sun-Saturn sky separation angle
Adds a column containing the angular separation on the sky from
Saturn to the Sun, in degrees. A Sun-Saturn value near zero
corresponds to solar conjunction; a value near 180 corresponds to
opposition.
-
Moon-Saturn sky separation angle
Adds a column containing the angular separation on the sky
from Saturn to the Moon, in degrees.
You may also include the positions of any set of inner Saturnian moons
in the table. Up to four pairs of quantities can be tabulated for each
selected moon:
-
RA and dec
Adds a pair of columns containing the J2000 right ascension and
declination for each selected moon. RA values are given in units of
hours; dec values are given in degrees.
-
Offset RA and dec
Adds a pair of columns containing the positional offset of each moon
from the center of the planet. Values are given in units of arcseconds,
where the first value is the offset in the direction of increasing J2000
RA and the second is in the direction of increasing dec.
-
Sub-solar latitude and rotating longitude
Adds a pair of columns containing the sub-solar latitude and
longitude on the selected moon, in degrees. These are measured in a frame
rotating with the body.
-
Sub-Earth latitude and rotating longitude
Adds a pair of columns containing the sub-Earth latitude and
longitude on the selected moon, in degrees. These are measured in a frame
rotating with the body.
Finally, click on the box to the left of each moon that you wish to
include in the table. Note that it is not necessary to include any
moon columns at all.
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Last updated 30 August 2007
Mark Showalter