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Mercury and Regulus

September 8, 2011

Mercury is putting in a bright but short appearance in the dawn sky. The planet is quite low in the east as dawn twilight begins to brighten, but it’s also quite bright. In fact, with Venus hidden in the Sun’s glare, Mercury’s the third-brightest object in the night sky right now, after the Moon and the planet Jupiter.

And tomorrow, it’s especially easy to pick out because it has a prominent companion: Regulus, the brightest star of Leo, the lion. It’s less than a degree to the right of Mercury — less than the width of a finger held at arm’s length. Regulus is only about one-seventh as bright as Mercury, but if you have a clear horizon, the pair will be pretty easy to pick out.

Mercury and Regulus won’t hang out together for long, though.

Mercury is dropping toward the Sun as seen from Earth. It’ll loop behind the Sun on the 28th, then climb into view in the evening sky in late October.

Regulus, though, is climbing away from the Sun. It rises four minutes earlier each day, so within a couple of weeks it’ll be well up in the sky by first light. And by March, it’ll be in the same position at the end of evening twilight, as the lion roars through the nights of spring.

For now, look for Regulus in the dawn sky, near the bright planet Mercury. If you miss them tomorrow, try again on Saturday, with Regulus standing a few degrees above Mercury.

Tomorrow: A star with a double identity.


Script by Damond Benningfield, Copyright 2011


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