Long Term Almanac for Sun and Moon  V1.04
Copyright © 2001, 2002 Henning Umland

y m d h m s s
 Date:        Time (UT1):         Delta T:         
GHA SHA Dec SD HP Equation of Time
Sun
Moon   Illum. 
Aries
-----------------------------------------------------------------------
GAST GMST Eq. of Equinoxes


Description:

This computer almanac calculates Greenwich hour angle, siderial hour angle, declination, semidiameter, and horizontal parallax for sun and moon and, moreover, the Greenwich hour angle of the vernal point (first point of Aries), siderial time (apparent and mean), current values for equation of time and equation of the equinoxes, and the illuminated fraction of the moon's disk.

The almanac, which is based upon formulas published in Astronomical Algorithms by Jean Meeus, can be used for centuries, provided the Delta T value (= TDT-UT1) for the given date is known. An accuracy of approx. ±1s is sufficient. Measured and predicted values are published on the web site of the IERS Rapid Service / Prediction Center. The documents are titled "monthly determinations of Delta T" and "long-term predictions of Delta T" and can be stored as text files (deltat.data.txt and deltat.preds.txt). Delta T was 63.8s at 2000.0 and is presently increasing by approx. 0.7s per year.

The program regards any blank dialog box in the time input field as zero. A missing year, month, or day will result in an error message (calculation must be restarted). The number of the year must be entered in 4-digit format.

An increasing or decreasing illuminated fraction of the moon's disk is indicated by a "(+)" or "(–)", respectively.

Accuracy:
GHA, SHA, and Dec of the sun: approx. ±0.02´
GHA, SHA, and Dec of the moon:    approx. ±0.15´
GHA Aries:    approx. ±0.01´
HP and SD: approx. ±0.01´
Equation of time: approx. ±0.1s
GAST: approx. ±0.001s
GMST: approx. ±0.001s
Equation of the equinoxes: approx. ±0.001s

GHAAries and SHA refer to the true equinox of date.

This program is freeware and may be copied and distributed in unmodified form and on a non-profit basis. For your private use, feel free to modifiy the source code according to your requirements. Any commercial distribution requires the author's permission.

Henning Umland      N 53° 20.6´   E 9° 52.0´       e-mail: mail@celnav.de

Check this web site for updated versions: http://www.celnav.de

Warranty disclaimer:
Results obtained with this program have been cross-checked with Multiyear Interactive Computer Almanac 1.5 by USNO. However, the program is still experimental and may contain errors leading to unexpected results in rare cases. Use at your own risk.

Warning:
Editing and modifying the JavaScript code may lead to unpredictable results. Users who are not familiar with JavaScript and calculations of ephemerides are strongly advised to leave the code unchanged.