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Mercury aglow in the evening sky

The innermost planet puts on its best evening show of 2010 in late March and early April.
April 2010 Venus finder chart
Venus points to Mercury in early April, serving as a helpful guide to the innermost planet.
Astronomy: Roen Kelly
April 1, 2010
For those who like to hunt for treasure, late March and early April offer nice views of the solar system's most elusive naked-eye planet. Mercury climbs into view in the west at the end of March, appearing as a pale-yellow dot low in the evening twilight.

Although Mercury shines brightly, it can be hard to pick out against the twilight glow. Fortunately, the planet Venus serves as a terrific guide this year. Venus shines brighter than any other point of light in the sky. Head outside about 30 minutes after sunset, find yourself an observing location with an uncluttered western horizon, and the brilliant planet will dazzle your eye.

During the final week of March, Mercury lies to the lower right of Venus. Although Venus gleams more than 10 times brighter than Mercury, you should be able to spot Mercury without much difficulty. According to Astronomy magazine senior editor Michael E. Bakich, "If you don't see Mercury right away, try finding it with binoculars. Once you know where it is, Mercury will pop into view."

Observing podcast: See Mercury and Venus in your night sky

Mercury reaches the peak of this evening appearance April 8, when it lies farthest from the Sun and climbs highest in the twilight sky. It then appears about 12° — slightly more than the angle covered by your closed fist held at arm's length — above the horizon 30 minutes after the Sun sets. Look for it to the right and slightly below Venus. Mercury remains near this altitude for about a week on either side of the 8th.

Once you spot Mercury, you may wonder why it has a reputation for being elusive. It is, after all, one of the brightest objects in the sky. Unfortunately, this bright light never climbs high in the sky. Mercury orbits closer to the Sun than any other planet, so, from our perspective on Earth, it never strays far from the Sun's glare. Even at its best, the innermost planet lies low in the west shortly after sunset or low in the east before sunrise. It never gets far enough from the Sun to appear high in a totally dark sky.

The great astronomer Nicolas Copernicus — the man who put the Sun in its proper place at the center of the solar system, with Earth circling it — reputedly never glimpsed Mercury. So take a few minutes one of these chilly February evenings, and catch a sight few people ever have.
Fast facts about Mercury:
  • It orbits the Sun at an average distance of 36 million miles, but covers a broad range from 29 million miles to 44 million miles.
  • Mercury takes just 88 days to complete one orbit of the Sun.
  • Mercury takes 59 days to rotate once on its axis.
  • With a diameter of 3,032 miles (38 percent of Earth's), Mercury is the smallest planet in the solar system.
  • Humans got their first close-up look at Mercury in March 1974 when NASA's Mariner 10 spacecraft flew by it and revealed a heavily cratered surface.
  • NASA launched the MESSENGER spacecraft toward Mercury in August 2004. It will go into orbit around the innermost planet a year from now (in March 2011), examining its surface, probing its interior, and measuring its magnetic field.
StarDome
Expand your observing with these online tools from Astronomy magazine
  • StarDome: Find Mercury in your night sky with our interactive star chart. Under "Options," select "Show names," select "Mark one specific object." Scroll down the list of Planet/Object Selection, highlight "Mercury," and click "OK."
  • Sign up for our free weekly e-mail newsletter to stay up to date on more great sky events.
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