RA to GHA Converter 1.04 – Copyright © 1999-2016 Henning Umland
Right Ascension of body    h   min   sec 
Greenwich Siderial Time (App.)    h   min   sec 

Greenwich Hour Angle of body    °   '   '' 

This calculator has been developed primarily to extract the Greenwich Hour Angle, GHA, of a celestial body from MICA (Multiyear Interactive Computer Almanac) in a convenient way, but it can be used in combination with other almanac software or printed almanacs as well.

Unlike the Nautical Almanac and ICE (Interactive Computer Ephemeris), MICA only provides the Right Ascension, RA, of a body which is the equivalent to the Siderial Hour Angle, SHA, with the exception that RA is measured in hours (0 - 24) eastward from the Vernal Equinox (first point of Aries) whereas SHA is measured in degrees (0 - 360) westward from the vernal equinox.

SHA[°] = 360 – 15 · RA[h]

Converting RA to GHA requires Greenwich Siderial Time, GST, (also provided by MICA), the Greenwich hour angle of the vernal equinox measured in hours (0 - 24) westward from the Greenwich meridian (1h is equivalent to 15°).

GHAAries[°] = 15 · GST[h]

GHA = SHA + GHAAries

When using MICA, RA can be accessed through the following menus and submenus:
(select object)
Equator of date

Greenwich apparent siderial time is available through:
Time and orientation
Siderial time (App.)


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