How to calculate the declination of the Moon?

Question by Montana B: How to calculate the declination of the Moon?
I would like to be able to predict the date of the next lunar eclipse, either via calculator or via a VB.Net program. I already have the declination of the Sun nailed down, so this is the only other thing I would need to make a prediction.
Great post, but I was kind of hoping maybe someone would have a simpler way to calculate this, maybe i'm too lazy but the algorithm seems a little long.


Best answer:
Answer by bikenbeer2000It might be easier to work with ecliptic longitude and latitude, rather than right ascension and declination. That way, the latitude of the Sun is automatically zero and you only need to search for times when the Sun and Moon are 180º apart in ecliptic longitude, with the Moon's latitude less than 1º 37', which means an eclipse is possible. Don't forget that, for lunar eclipses, you're only interested in geocentric positions of the Sun and Moon. For an observer on the Earth's surface, the Moon's coordinates can vary by up to 1º from the geocentric position. Some formulae for the Moon's coordinates are given at this website: http://stjarnhimlen.se/comp/ppcomp.html
[Later]
You could shorten the algorithm, but you would lose accuracy. Referring to the website, if you ignore the perturbations of the Moon, you probably wouldn't miss the dates of many lunar eclipses, but the calculated time might be up to 4 hours out. When writing a program, these perturbation terms can be added as a subroutine, since this stage of the calculation is essentially repetetive.

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