Observing Challenge: Sighting Extremely Slender Moons Part I

   We here at Astroguyz always love a good challenge. Maybe I’ll never climb Everest or run an ultra marathon in Death Valley, but visual observation challenges happen in our local sky nightly. One challenge that has come to my attention lately is the fine art of sighting an extremely slender new or old moon in the dawn or dusk sky. This is harder than it sounds; the the moon may seem bright when placed against the night sky, but it actually quite hard to spot when placed in bright twilight. Such sightings may be considered as the vanguard of what’s possible with the human eye. In fact, the record for new moon sighting with optical aid stands at 11 hours and 40 minutes past new set by Mohsen G. Mirsaeed with giant binoculars on September 7th, 2002, and 15 hours and 32 minutes set by Stephen O’Meara on May 1990 with the naked eye.

The theoretical limit, known as the Danjon Limit (Not to be confused with the Danjon Number!) that a new or old moon can be sighted is generally accepted at 6.5 degrees of arc separation from the sun. Computing this against a synodic month, as opposed to a draconitic, anomalistic, or tropical month, of 29.53 days, we get a limit of 12 hours and 48 minutes under ideal conditions to sight a new Moon.

So imagine my surprise as a read a recent Sky & Telescope article in the February 2008 issue; apparently there is a very good chance of the Eastern Maritimes having a shot at the binocular record by a few minutes on May 5th! My proposal is to attempt this record from the top of Haystack Mountain in Mapleton, Maine. At 1,341 feet of elevation, it should give me an unobstructed horizon, and perhaps a tiny bit more boost in elevation. The window will be slim; less than ten minutes. I’ll be using my Canon Image Stabilized 15×45 binocs, and anyone who wants to make the attempt with me just leave a comment on this site, and we’ll mount an expedition!

For practice, I’ve been attempting to sight New and Old Moons of lesser difficulty on the months leading up to May 5th; note from the chart above that I wasn’t successful  for the Old Moon on March 6th. I saw Venus here from the shores of Saint Froid Lake and the future site of the Twin Dogs Observatory, but no thin waning crescent Moon. I would bet that trees on the horizon across the lake were the culprit. Only three tries left before the big one! Anyhow, I’ll post my results in a follow up piece in May. Now, to pray for clear skies…   

The project Moon watch site, which has more info on this feat as well as sighting report forms, can be seen at the following link;

http://www.crescentmoonwatch.org/index.htm