Bob Moler's Ephemeris Blog

Monday, March 7th.  The sun will rise at 7:09.  It’ll be up for 11 hours and 28 minutes, setting at 6:37.   The moon, 3 days past new, will set at 9:49 this evening.

The moon tonight will appear as a thin sliver, with not much visible on the thin illuminated portion.  However if as you look at the moon tonight you have the funny feeling that the whole moon is visible, you are right.  It’s easily confirmed with a pair of binoculars or a small telescope.  What is illuminating the dark part of the moon is earthshine.  The earth is big and bright in the moon’s sky, and nearly full from its vantage point.  The effect used to be called by the term “Old moon in the new moon’s arms”.  The effect was first explained by Leonardo DaVinci some 500 years ago.  The effect will disappear in a few days as the moon gets brighter and the earth less so in the moon’s sky.  Earthshine will appear again when the moon appears as a waning crescent in the morning.

* Times are for the Traverse City/Interlochen area of Michigan.  They may be different for your location.

Update:

Earthshine is notoriously hard to photograph.  Here’s one of mine from 1991.  Part of a planetary conjunction picture with a short focal length telephoto lens.  I’ve cropped out the planets.  The sunlit side of the moon is vastly overexposed causing the blooming in the photograph.

Earthshine on the crescent moon