Volume 14, Issue 8 ~ February 23 - March 1, 2006

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Sky Watch

by J. Alex Knoll

Misunderstood Mercury

The waning crescent moon rises a few hours before sunrise leading to Monday’s new moon. Friday you’ll find the moon low in the southeast at 6am with Venus a little more than 10 degrees higher. The following morning you’ll be hard pressed to spot the sliver of moon rising around 6:30, and this time Venus shines not only higher but farther west.

A thin waxing moon reappears above the western horizon Wednesday, March 1, as the sun sets at 6pm. Look between the outer edge of the moon’s narrow crescent and the horizon for a brilliant light. Brighter than any star, this is Mercury, which Friday reached its zenith of 18 degrees above the horizon.

Despite Mercury’s relative proximity to earth, it is one of the least explored planets, except for Pluto, which even now is the target of the New Horizons space probe launched last month and destined to reach that farthest planet by 2017. NASA launched a second Mercury probe in 2004, Messenger, which will begin orbiting in 2011.

The first in 1974 and 1975, Mariner 10 circled Mercury three times. But even so, less than half of the planet’s surface was photographed. The probe measured the most extreme temperature shifts in the solar system with daytime highs of 842 degrees Fahrenheit and nighttime lows of 292 degrees below zero.

Such extremes in temperature and such closeness to the sun have allowed little atmosphere to form around Mercury. What exists are atomic particles of sodium, helium and hydrogen blasted from the planet’s surface by the solar wind.

Of all the planets, Mercury alone has no moon. If one ever existed, it long ago succumbed to the sun’s much stronger gravitational pull. At 3,013 miles in diameter, Mercury is roughly the size of our moon. Additionally, its surface is ancient and scarred with countless craters.

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