76ebd569d5
To obtain the sun's true longitude, the Star::getlonEcl() function has been
created. The moon's age is then calculated as the difference between the moon's
and sun's true longitudes. The phase is then simply half of one minus the
cosine of the age. Hence these calculations are very cheap compared to the rest
of the moon position calculations. The algorithm is from:
Duffett-Smith, Peter. Practical Astronomy With Your Calculator. 3rd ed.
Cambridge: Cambridge University Press, 1981. ISBN 0-521-28411-2.
The code can replicate the example in the book of Feb 26, 1979 at 16h UT, with
an age of -0.4767 degrees a phase of 0.0:
$ fgfs --aircraft=UFO --start-date-gmt=1979:02:26:16:00:00 --airport=EGLL \
--altitude=50000 --enable-hud
The calculated phase is 1.459e-5 and the age is -6.2908 (which is -0.43628
degrees). For a recent full moon:
$ fgfs --aircraft=UFO --start-date-gmt=2015:11:25:22:44:00 --airport=EGLL \
--altitude=50000 --enable-hud
The calculated age is -3.1413 and the phase is 0.9999999778.
SimGear - Simulator Construction Tools ====================================== http://www.flightgear.org SimGear is a set of open-source libraries designed to be used as building blocks for quickly assembling 3d simulations, games, and visualization applications. SimGear is developed by the FlightGear project and also provides the base for the FlightGear Flight Simulator. Source code for SimGear is released under the GNU Library General Public License (LGPL) - see COPYING for license details. See INSTALL file for help on building SimGear.