Crescent moon with Earthshine and Venus — Bob King / News Tribune
This weekend marks the return of the crescent moon to the evening sky. Although the weather forecast through Sunday doesn’t look favorable for the Northland, others outside the region might find clear skies. If you’re in a cloud-free location, look low in the western sky tonight about a half hour after sunset (around 6:30-7 p.m.) for a delicate fingernail moon.
By Monday, when the weather is expected to clear off, the crescent will be much higher and easier to see. Maybe some of you have noticed that when the moon is in crescent phase, its entire outline is visible, only darkly. While the bright crescent is illuminated by sunlight reflected off the moon’s surface, the dark portion is lit by Earthshine. Sunlight reflects off the Earth’s clouds and oceans, back into space and all the way out to the moon. There it’s reflected back to us again as a dim, dusky glow.
Just for fun, take a pair of binoculars or small telescope and examine this "dark side" of the moon. There’s just enough light there to discern a surprising number of lunar features. Now imagine yourself an astronaut on the moon, standing on the wall of a lunar crater in the eerie blue Earthlight, looking back at our planet aglow against the black sky. Takes your breath away.