主题：科学英语:每日星相(6.30)

每日星相

Daily Astronomy

规则：参与的朋友可以每人翻译一句，也可全部翻译，依照自己情况而定。
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说明：每天悬赏50分。

The moon still close to white-hot Spica

Tonight is Tuesday, Jun 30 2009

If you took the time machine into the past last night with the bright star Spica, you noticed the waxing gibbous moon was to the west (or right) of Spica. Tonight the moon is to the east (or left) of Spica. This motion of the moon on our sky’s dome is due to the moon’s actual motion in orbit around Earth.

The Moody Blues refer to the moon as the “cold hearted orb that rules the night,” but the same can hardly be said for Spica. About 2,200 times as bright visually as the sun, Spica also is one of the hottest stars visible to us, with a surface temperature of more than 22,000 kelvins. That’s nearly four times our sun’s surface temperature. Spica is so hot that a large part of its energy manifests is ultraviolet rather than visible light. In actuality, Spica’s total energy output is about 15,000 times that of the sun.

But that’s not a totally fair comparison, because Spica is not just one star, but a spectroscopic binary. That means that there are really two hot blue-white stars orbiting so close that they cannot be separated in in a normal telescope, and their binary nature is discernible only through an analysis of their light.

Written by Larry Sessions , 30 June 09