Earthshine, Crescent Moon and Mercury

October 27, 2016

Mercury moon conjunction 092916 6 (1)

Photographer: Emily Belanger
Summary Authors: Emily Belanger, Pam Tomkinson, Donald Tomkinson, Gareth Packard, John Stetson

Shown above is the conjunction of the crescent Moon and Mercury as observed during the early morning hours of September 29, 2016, from Land's End, Harpswell, Maine. Mercury (at top left) was positioned but seven-tenths of a degree (about one and a half lunar diameters) above and to the right of the Moon, which was just 2 percent illuminated. Nonetheless, a 2.5-second exposure revealed detail over the entire lunar disk. Leonardo Da Vinci recognized that this dim illumination of the unlit Moon (in the crescent phase) resulted from earthshine. Because the brightness (albedo) of the Earth slightly changes in accordance with the percentage of cloud cover, snow cover and other factors, how bright earthshine appears from one lunar cycle to the next also changes. It's typically a little brighter in early spring when both snow cover and cloud cover are extensive over the Northern Hemisphere. Look for the conjunction of Jupiter and the crescent Moon on the morning of October 28.

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