It was cloudy all day here in Tucson, but around sunset the clouds moved out leaving behind a starry sky. I decided to take out the Stellarvue 90mm Triplet to check out the crescent moon for a few minutes. As I headed outside around 8:15 PM MST (0315 UT 4/17/2010) one of the first things that caught my attention was how bright the earthshine was on the moon tonight. The moon is sitting just below the Pleiadas star cluster and together with Venus the western sky is lovely.
Wikipedia has a detailed entry regarding earthshine that is worth the read. "Earthshine is most readily observable shortly before and after a New Moon, during the waxing or waning crescent phase. When the Moon is new as viewed from Earth, the Earth is nearly fully lit up as viewed from the Moon. Sunlight is reflected from the Earth to the night side of the Moon. The night side appears to glow faintly and the entire orb of the Moon is dimly visible. It is also known as the Moon's ashen glow or as the old Moon in the new Moon's arms."
Virtual Moon Atlas (which I highly recommend) and represents the phase of the moon tonight. If you click on the thumbnail and look closely at about 10 o'clock just in from the lunar limb, you can see an area that is slightly brighter than its surroudings. In the telescope, the spot was much brighter than in the image.
Thanks to Virtual Moon Atlas, I quickly ascertained that the bright spot I was seeing was likely the crater Aristarchus. Aristarchus is a prominent lunar impact crater that lies in the northwest part of the Moon's near side. It is considered the brightest of the large formations on the lunar surface, with an albedo nearly double that of most lunar features. The crater is located at the southeastern edge of the Aristarchus plateau, an elevated area that contains a number of volcanic features, such as sinuous rilles. This area is also noted for the large number of reported transient lunar phenomena, as well as recent emissions of radon gas as measured by the Lunar Prospector spacecraft.