Astro Bob's Backyard Astronomy: Atmospheric Funhouse Mirrors and a Suspicious Constellation
There’s a full moon tonight.
Clouds are in the forecast, but keep your fingers crossed for a parting soon after six. If the horizon line is clear at moonrise (6:19pm on Tuesday, March 7th) observers could be in for an illusion as performed by Earth’s atmosphere. “When you first see the moon breach the horizon, you're not actually seeing the real moon - that is an optical illusion,” says Bob King. “You're actually seeing the effect of the air refracting the moon upwards.” The result is an oblong looking moon during those first moments of moonrise.
Whether or not you’re able to see the moon tonight, you’ll still be able to ponder about the suspiciously concentrated stars that make up the Big Dipper. Perhaps that constellation has almost seemed a little too conveniently constructed. There’s a reason for that. “If you subtract the top star of the bucket and the star at the end of the handle,” says King. “Those five [remaining] stars of the Dipper are actually members of an old star cluster.” The stars have been drifting away from each other and have serendipitously organized themselves between the two other stars to create the cosmic vision that we see today. "The Dipper is one of those unusual cases where most of the stars are actually related to one another."