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The Heavens’ Only Green Star

Libra’s Zubeneschamali is unique

If you’re up before the sun, you can’t miss Venus, which rises in the southeast by 6am. A half-hour later, this Morning Star is ablaze a good 30 degrees above the horizon, brighter than anything but the moon and the coming sun. As the horizon brightens, Venus climbs higher, growing dimmer until blinking out of view by 7:30am. Wednesday morning, January 29, look for Venus just four degrees above a thin, waning crescent moon before dawn.
    Earlier in the week, Saturday before dawn, the moon passes just a couple degrees above golden Saturn in the constellation Libra. The cosmic scales are the only inanimate object among the zodiacal constellations. Long ago the scales were part of Scorpius, its outstretched claws. But then Roman astronomers in the first century BC designated them their own constellation. A relatively faint constellation, Libra has no first-magnitude stars. The brightest, Zubeneschamali or Beta Librae, shines at magnitude 2.7. It is the only star that appears to shine green.
    As twilight gives way to darkness, Mercury appears low in the west-southwest. Mercury (magnitude –0.9) is emerging into twilight view after sunset. Look for it above the west-southwest horizon within an hour after sunset, inching a little higher and staying visible a little longer over the coming week. Off to Mercury’s left and almost as bright is Fomalhaut in the constellation Piscis Austrinus dubbed the Lonely Star for its lack of bright stellar neighbors.
    Jupiter reigns through the night, appearing in the east at sunset and directly overhead around 11pm.
    Mars rises before midnight, but it takes another hour or more before the red planet is high enough above the southeast horizon for easy viewing. Look to the lower left of Mars for the bright star Spica, a half-dozen degrees away.