Expert: Philip Stahl - 8/10/2007

Question
Hello,

A few times a year, the moon will rise behind Mt. Baker (WA) USA, and it looks incredible from the local airport in Abbotsford (CYXX) BC, Canada.

How could I calculate the next time it happens.

I know the Lat/Long of CYXX Latitude = 49.03N / Longitude = 122.37W and the elevation is 195 feet

I know the lat/long of mt baker: 48.8° N, 121.8° W and the elevation is 10781 ft



David

Answer
Hello,

Calculating the Moon's position for a given latitude and longitude is an *extremely* complicated process - much more difficult than merely changing from one coordinate system to another for a terrestrial observer. (Say from the horizon system to the Right Ascension-Declination system).

I therefore suggest that instead you get hold of a good computer program which can perform the calculation for you.

"Cybersky" (available online) is one such program which will perform the computations for a number of major cities close to your location, e.g. Edmonton, Vancouver, Seattle etc. This may be close enough to obtain a decent answer.

You may also wish to check the site below, which will have a lunar position ephemeris.

http://www.programurl.com/software/ephemeris.htm

Another option is to check with the U.S. Naval Observatory in Washington, DC and inquire whether they can provide an ephemeris for lunar positions, and times, meeting your conditions.


Good luck!