Brought to you by Starry Night

Tuesday, May 23

The solar system's innermost planet Mercury is making its way higher each night into the western sky right after sunset. You'll have to look fast though. This window of opportunity to see Mercury in the Northern Hemisphere lasts less than a month.

Mercury passed in front of the sun (superior conjunction) on May 9. It became a target for viewing about May 21, though it was very low in the west and still awash in the sun's glare.

Tonight, however, may be the best time to begin looking for Mercury. It should appear around 20 to 30 minutes after sunset, some 10 degrees above and to the left of the sunset point. (10 degrees is about the width of a fist held out at arm's length.)

Don't be confused by the stars Capella, which will be well to the north of the sunset point, or Betelgeuse, which lies south of it. Pollux, too, may confuse you, but it rides well above the western horizon, too far from the sun to be Mercury.

By the end of the month, Mercury sets about two hours after the sun does. It remains visible until about the middle of June, when it is finally lost in the sun's glare. On June 4, a young crescent moon lies south of Mercury and should be a beautiful sight.

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Jeff Kanipe is the author of A Skywatcher's Year, an astronomy guide just published by Cambridge University Press. He is a former editor at Astronomy and StarDate magazines and a writer for the Earth & Sky radio series.

The images in Skywatch are produced by Starry Night software.