LONG-TERM ALMANAC FOR SUN, MOON, BRIGHTER PLANETS, AND POLARIS  V1.17
 Copyright © 2001−2016 Henning Umland

Description:
This computer almanac is based upon the VSOP87D Theory, the 1980 IAU Nutation Theory, the ELP2000 Theory (truncated) and formulas published in Astronomical Algorithms by Jean Meeus. The program calculates Greenwich hour angle (GHA), right ascension (RA), and declination (Dec) for Sun, Moon, Venus, Mars, Jupiter, Saturn, and Polaris (apparent positions).

Further, the following quantities are provided:

Geocentric semidiameter (SD) and equatorial horizontal parallax (HP) for Sun, Moon, and planets
Equation of time
Illuminated fraction of the apparent disks of Moon and planets
Phase of the Moon
Greenwich apparent sidereal time (GAST)
Greenwich mean sidereal time (GMST)
Equation of the equinoxes (= GAST−GMST)
Nutation in longitude (Δψ)
Nutation in obliquity (Δε)
Mean obliquity of the ecliptic
True obliquity of the ecliptic (= mean obliquity + Δε)
Julian date (JD)
Julian ephemeris date (JDE)
Geocentric lunar distance of the sun (center−center)
Day of the week

The phases of the Moon are indicated as follows:

New
+cre = waxing crescent
FQ = first quarter
+gib = waxing gibbous
Full
–gib = waning gibbous
LQ = last quarter
–cre = waning crescent

By definition, the phase is defined by the difference between the ecliptic longitudes of Moon and Sun. It does not exactly correlate with the illuminated fraction of the Moon's disk since the plane of the Moon's orbit is inclined to the ecliptic.

GHA and RA refer to the true equinox of date.
The apparent positions of the planets refer to the respective center. A phase correction is not included.

The apparent semidiameter of Venus includes the cloud layer of the planet and may be slightly greater than values calculated with other software (referring to the solid surface). The semidiameters of Jupiter and Saturn refer to the respective equator.

The almanac can be used for many decades, provided the ΔT value (= TT–UT1) for the given date is known. An accuracy of approx. ±1s is sufficient for most applications. Errors in ΔT have a much greater influence on the coordinates of the moon than on the other results. ΔT is obtained through the following formula:

ΔT = 32.184s + (TAI−UTC) − (UT1−UTC)

Current values for TAI−UTC and UT1−UTC are published on the web site of the IERS Rapid Service / Prediction Center (IERS Bulletin A).

Since ΔT is subject to random changes, reliable long-term predictions are not possible. Here are some ΔT values of the past:

1970.0:  +40.2s
1975.0:  +45.5s
1980.0:  +50.5s
1985.0:  +54.3s
1990.0:  +56.9s
1995.0:  +60.8s
2000.0:  +63.8s
2005.0:  +64.7s
2010.0:  +66.1s
2015.0:  +67.6s
2016.0:  +68.1s

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

LICENSE

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the license or any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License (http://www.gnu.org/licenses/) for more details.

Henning Umland    N 53° 20' 34''   E 9° 52' 00''

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