Cassini/Saturn Ephemeris Generator 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"); introduction of the Ephemeris Generator for Cassini.
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.
2.4 (December 1, 2009): Updated the default ephemerides. To reduce confusion, we have removed the choice about what ephemeris to use.
2.5 (January 23, 2013): Anthe and Aegaeon added. Raised the maximum number of output lines to 10,000. Renumbered for consistency across all the Ephemeris Generator tools. Ephemeris updates.
2.6 (January 4, 2016): Ported to new server. Ephemeris updates.
2.7 (October 14, 2020): Ephemeris updates.
2.8 (June 20, 2021): Ephemeris updates.
3.0 (August 2, 2022): Major new features:
- the selection of available columns has been expanded and standardized across all Ephemeris Generator tools.
- Ephemeris Generator requests can now be bookmarked.
- the new Output option lets you jump directly to the table, bypassing the web page.
- JWST, HST, and Earth-based observatories are now supported.
- the form now uses a clean, new style sheet.

Time Limits

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 (ISO format)
MJD 42963.00071759259
JD 2442963.50071759259

If you want the gory details of how times are interpreted, click here.

Interval: 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. Start times and intervals are rounded to the nearest minute.

General Column Selection

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.
Year, DOY, Hour, Minute
Adds four columns containing the UTC date (year and day-of-year) and time (hours, minutes) as integers.
Year, DOY, Hour, Minute, Second
Adds five columns containing the UTC date (year and day-of-year) and time (hours, minutes, seconds) as integers.
Observer-Saturn distance
Adds a column containing the distance between the observer and Saturn, in km.
Sun-Saturn distance
Adds a column containing the distance between the Sun and Saturn, in km.
Saturn phase angle
Adds a column containing the phase angle of Saturn as seen from the observer, in degrees. This is equal to the Sun-Saturn-observer angle.
Ring opening angle to the observer
Adds a column containing the ring plane opening angle to the observer, in degrees. This is equivalent to the planetocentric sub-observer latitude at Saturn; it equals zero during a ring plane crossing.
Ring opening angle to the Sun
Adds a column containing the ring plane opening angle to the Sun, in degrees. This is equivalent to the planetocentric sub-solar latitude at Saturn; it equals zero during a ring plane crossing.
Sub-observer inertial longitude
Adds a column containing the sub-observer 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 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-observer latitude and rotating longitude
Adds a pair of columns containing the sub-observer planetocentric latitude and longitude at Saturn, in degrees. This is measured in a frame rotating with the planet.
Sub-solar latitude and rotating longitude
Adds a pair of columns containing the sub-dolst planetocentric latitude and longitude at Saturn, in degrees. This is measured in a frame rotating with the planet.
Saturn RA and Dec
Adds two columns containing the J2000 right ascension and declination of Saturn. RA is tabulated in units of hours; declination is in units of degrees.
Earth RA and Dec
Adds two columns containing the J2000 right ascension and declination of the Earth. RA is tabulated in units of hours; declination is in units of degrees.
Sun RA and Dec
Adds two columns containing the J2000 right ascension and declination of the Sun. RA is tabulated in units of hours; declination is in units of degrees.
Saturn projected equatorial radius
Adds a column containing the projected equatorial radius of Saturn as seen from the observer, in degrees.

Moon Column Selection

You may also include the positions of any set of moons in the table. Any of these quantities can be tabulated for each moon:

Observer-moon distance
Adds a column containing the distance between the observer and the moon, in km.
Moon phase angle
Adds a column containing the phase angle of the selected moon as seen from the observer, in degrees.
Sub-observer latitude and rotating longitude
Adds a pair of columns containing the sub-observer planetocentric latitude and longitude at the selected moon, in degrees. This is measured in a frame rotating with the moon.
Sub-solar latitude and rotating longitude
Adds a pair of columns containing the sub-dolst planetocentric latitude and longitude at the selected moon, in degrees. This is measured in a frame rotating with the 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 selected moon from the center of the planet. Values are given in units of degrees, where the first value is the offset in the direction of increasing J2000 RA and the second is in the direction of increasing dec.
Orbital longitude relative to observer
Adds a column containing the orbital longitude of the selected moon relative to the observer, in degrees. Zero indicates that the moon is between the observer and the planet; 90 indicates that the moon is at the receding ansa.
Orbit plane opening angle to observer
Adds a column containing the opening angle of the orbit plane as seen from the observer, in degrees.

Moon Selection

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.

Output

By default, when you click on "Generate table", you are directed to a web page that lists the details of the request and a small preview. Optionally, you can choose to bypass the web page and go directly to table format.