This week, the moon will have two ?close encounters? with spectacular star clusters.
On Saturday evening, March 20, look for the thin crescent moon as soon as the sky begins to get dark after sunset. You will see the moon right in front of the Pleiades, the brightest star cluster in the sky.
The Pleiades, number 45 in Charles Messier?s famous catalog of deep sky objects, has been known since antiquity. It is one of the closes star clusters to our sun, 410 light-years distant in the constellation Taurus.
Look for ?the old moon in the new moon?s arms.? It is the part of the moon not in sunlight, but illuminated by earthshine, sunlight reflected from the nearly full Earth in the lunar sky.
If you watch closely with a telescope, you may actually witness a lunar occultation as the moon passes in front of one or more stars. Notice how the stars wink instantaneously out, proof of the moon?s lack of an atmosphere.
Two nights later, on Monday March 22, the moon will be approaching another star cluster, Messier 35 in Gemini. This cluster is larger and richer in stars than the Pleiades, but is much farther away, 2,800 light years from the sun. The moon will be a wider crescent, and the earthshine less pronounced. As the night progresses, the moon will draw closer to M35, passing closest around the time of moonset for new world observers.
Both these events will be beautiful to see. The Pleiades encounter can be appreciated with the naked eye or binoculars; the M35 encounter will be best in binoculars or a small telescope.