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Mercury's March madness

The closest planet to the Sun shines brightly in the twilight sky.
Mercury March 2005 finder chart
THE MOON BRUSHES MERCURY the evening of March 11, a great time to spy the elusive inner planet.
Astronomy: Roen Kelly
Mercury's March madness
MERCURY STANDS ABOVE the western horizon after sunset this month in its best evening appearance of 2005.
Lee Coombs
March 10, 2005
Mercury — the closest planet to the Sun — makes its best evening appearance of the year this month. Half an hour to an hour after sunset, look low in the west for a bright dot piercing the deep orange to blue twilight sky. The planet was brightest March 1 when it stood 6° above the western horizon 30 minutes after sunset. (For comparison, your closed fist held at arm's length spans 10°.) Each day after March 1, Mercury fades a bit, but even 2 weeks later it will be brighter than any star in its area.

Mercury will be easiest to find March 11, when a 2-day-old crescent Moon lies nearby. You can spy Mercury 4° to the Moon's lower right, about 11° (a bit more than a fist's width) up from the horizon in the west. A view of Mercury through a telescope that evening will reveal the planet's small disk, which will appear 48-percent lit, similar to a quarter Moon.

The next evening, Mercury reaches a point called greatest elongation — its maximum distance from the Sun as seen from Earth. In the days following, Mercury remains fairly high but fades rapidly. On March 17 it lies 10° above the western horizon 30 minutes after sunset and sets 1 hour later. Mercury appears in front of the faint stars of Pisces the Fishes during this entire period of visibility.

Quick facts:
  • Mercury orbits the Sun every 87 days, 23 hours, and 18 minutes. For every 1 Earth "year," Mercury experiences 4.
  • Mercury's diameter is 3,032 miles, only 38-percent that of Earth's.
  • The largest crater on Mercury, named Beethoven, is the largest known crater in the solar system. Beethoven is nearly 400 miles in diameter.
  • From Mercury, the Sun is 6.3 times brighter than from Earth.
  • Mercury has a total of 297 named features, of which 239 are craters.
  • Mercury next will pass in front of (or, transit) the Sun November 8, 2006. This event will be visible from the United States.
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