Additional Information

Local calendar Date in the local calendar specified for the current observer in the Observer dialog. If the Julian/Gregorian calendar was chosen as the local calendar, dates between 15 October 1582 and the date of the local introduction of the Gregorian calendar (see Local calendar) are marked by an asterisk to avoid confusion. If no local calendar was specified for the current observer location the Local calendar checkbox is disabled.

delta T The value of delta T, the difference between ephemeris time (ET) and universal time (UT) in seconds (to 0.1) or hours, minutes, and seconds (hh:mm:ss), selected in the delta T dialog

Nutation in longitude and obliquity The nutation, the motion of the true pole of the earth's rotation about the mean pole, resolved into its components in longitude and obliquity in seconds to 0.1".

General precession General precession in degrees to 0.01", positive for dates before and negative for dates after J 2000 (2000 Jan 1, 12h UT).

Lunisolar precession Lunisolar precession in degrees to 0.01", positive for dates before and negative for dates after J 2000 (2000 Jan 1, 12h UT).

Longitude of mean sun The longitude of the ‘mean sun’, the sun with only its mean motion in longitude, without its ecliptic inequality.

Equation of time The equation of time, the difference in right ascension between the true sun and the mean sun moving uniformly in the equator, in seconds (to 0.1) or minutes and seconds (hh:mm:ss).

Longitude of mean sun:  The longitude of the mean sun, the sun with only its mean motion in longitude, without its ecliptic inequality, in degrees.

Apparent local time Apparent local time is measured from the upper meridian transit of the true sun at apparent noon and the lower meridian transit of the true sun at apparent midnight. It is the time kept by sundials and other astronomical methods of determining local time, and is nonuniform. It is not used for calculation by the ephemeris, but can be displayed as useful additional information. Apparent local time differs from mean local time by the equation of time: apparent local time = mean local time + equation of time, where the mean local time is for the exact longitude of the location set in the observer dialog. When the time shift is set to mean local time, by clicking the button next to sec in either the observer page or the starting date and time panel, and the equation of time is also displayed in minutes and seconds as additional information, this relation is evident. For example, select Paris (France) in the observer page, and click the button next to sec so that a time shift to mean local time of 0h 9m 19s appears. Enter 2004 3 (Mar) 1, 12h 0m as the starting date and time, and run the calculation, which gives:

mean local time 12:00 + equation of time -0:12:16 = apparent local time 11:47:44,which is consistent. However, when the time shift is set to a time zone, the time of which differs from the mean local time, the program still computes the mean local time for the exact longitude of the location and adds the equation of time, and the resulting apparent local time applies to the time in the time zone, which is not the same as the mean local time. For example, again select Paris (France) in the observer page, but now with the time zone of 1h 0m as the time shift. (Clicking the button next to sec in the observer page or the starting date and time panel also changes the previous setting of mean local time to the time zone.) Again, enter 2004 3 (Mar) 1, 12h 0m as the starting date and time, and run the calculation. The display is now:

time zone local time 12:00 + equation of time -0:12:17 = apparent local time 10:57:03,which does not appear consistent. But it is. Now, the difference between the time zone local time and mean local time in Paris is 1h 0m 0s - 0h 9m 19s = 0h 50m 41s. Hence, the computation of the apparent local time is:

time zone local time 12:00 - 0:50:41 =

mean local time 11:9:19 + equation of time -0:12:17 = apparent local time 10:57:02 (the display reads 10:57:03 due to converting decimal computations), which is the apparent local time corresponding to the time zone local time 12:00 in Paris. Obviously, it is more transparent to calculate the apparent local time from the mean local time, but the calculation from time zone local time nevertheless correctly gives the apparent local time corresponding to the time zone local time.

Greenwich mean sidereal time The Greenwich mean sidereal time (GMST), the hour angle of the vernal equinox at Greenwich, in hours, minutes and seconds.

Local sidereal time The local mean sidereal time (LMST), the hour angle of the vernal equinox for the longitude of the location set in the observer dialog, in hours, minutes and seconds.