Extreme Crescent Hunting Tips

Saber’s Beads: The “string of pearls” arc of illuminated lunar peaks seen prior to the first complete crescent. Note the striking resemblance to the moments just before and after a total solar eclipse. (27 May 2006. raw image credit: maurice collins/ltvt)​

The moonrise before and moonset after each New Moon offer stargazers the opportunity to view the thinnest lunar crescents. There are many websites and apps that provide exact moonrise/set data for any location. Here are some additional tips to maximize your chances of sighting our very young (or old) moon.

Set up at a site with as much altitude as possible overlooking an unobstructed horizon. Optimal sky transparency allows the crescent to be detected and tracked down to, or up from, the horizon. Using a telescope or binoculars (mounted binos are recommended), fine tune the focus on Venus, Jupiter, or one of the brighter stars beforehand. For dusk attempts, have Sol’s setting azimuth on hand- making note after sunset of a random landmark at that position for reference- as well as Luna’s altaz position at sunset thru moonset. Accordingly, for dawn attempts, have Luna’s altaz info for moonrise thru sunrise. As dawn slivers have the advantage of possible detection with dark-adapted eyes, wearing sunglasses during the day prior to sunset attempts is recommended for maximum ‘dusk’ adaptation. Once the crescent is acquired in binoculars, walk the bino down to the horizon/random landmark in consecutive FOVs for the approximate naked-eye altaz. A favorable elongation is important. In the 24 hours before or after New Moon, Luna’s angular separation from Sol can vary by several degrees. With a favorable ecliptic, net elongations (as altitude) of 6° or more at sunset or moonrise offer the best window for detection. Observers nearer to the equator than the poles enjoy a much greater frequency of steep ecliptics. Illuminated fractions of same-age crescents within 24 hours of New Moon can vary by 200% and a full magnitude of brightness due to distance, libration, and sun angle. Slivers near perigee help present a thicker and brighter lunar profile for personal record crescent spotting. Last but not least, don’t always count-out a shallow ecliptic. Occasionally our moon’s extreme northern or southern declination will compensate for a less than favorable ecliptic angle.


Another rare and challenging notch for ones lunar bedpost is to catch the consecutive waning and waxing crescents within 24 hours on each side of New Moon. For example, the July 2008 Buck Moon offered such an opportunity as I was able to spot both the -16.5 hour illumination before sunrise on the 2nd and the +23.5 hour sliver just after sunset on the 3rd. Clean horizons for both windows is a gift in itself.

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[exerpt from Saber Does The Stars by Stephen Saber] http://c14isawesome.blogspot.com