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Age of the moon |
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Calculates the age of the moon
function AgeOfMoon(Date:TDateTime):extended; function AgeOfMoonWalker(date:TDateTime):extended;
Description Calculates the age of the moon (in days) for the given time. I did find two different definitions for this number, thus there are two functions for calculating it. The correct definition of the age of the moon seems to be the straight-forward time since the last new moon.
However John Walker in his original Moontool did use a different one, which describes the position of the terminator on the moon - the apparent longitude of the moon - normalized on the mean length of the month instead of 360 degrees. The mean length of a month is 29.530589 days. As the moon orbit is both elliptical and also has quite a lot of variation due to perturbations from the sun both values differ significantly - only for an unpertubed moon in circular orbit they would be indentical.
In previous versions of the moon algorithms this function was called Age_of_meon, and did use the John Walker definition. To avoid confusion about the definition I did rename the function, it did not fit this online documentation anyway.
Reference This function is based upon chapters 47 (45) and 25 (24) of "Astronomical Algorithms". |