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Volume 14, Issue 33 ~ August 17 - August 23, 2006

Sky Watch

by J. Alex Knoll

Summer’s Lights Brighten Dark Nights

Imagine reading by Deneb’s starlight

A waning moon rises after midnight with week’s end and appears later and smaller until Wednesday’s new moon. Not only is the moon obscured in such tight quarters with the sun, four of the five naked-eye planets are also “invisible”: Mercury, Venus, Mars and Saturn all rise within one-half hour of sunrise, around 6:25 this week. Only Jupiter appears, low in the southwest at sunset, just before 8pm; within two hours, he, too, sets.

Dark summer skies like these are a perfect backdrop for exploring the stars and constellations. Three of the brightest stars, Deneb, Vega and Altair, form the Summer Triangle and are with us from dusk to dawn, appearing directly overhead at sunset and disappearing above the western horizon with daybreak. Vega is brightest, doubling Altair and tripling Deneb.

A bluish-white star in the constellation Lyra the lyre, Vega is fifth-brightest in the entire sky. However, it is only three times the size of our sun and 25 light years away.

The southernmost star in the triangle is Altair of Aquila the eagle. A yellow-white star, Altair is the 12th-brightest in all the heavens, not because of its mass, which is twice that of our sun, but instead because at 16.7 light years away, it is one of the closest stars to our solar system.

Deneb is the tail of Cygnus the swan, flying on outstretched wings through the night sky. Nineteen stars appear brighter than Deneb, but all are much closer to us. Located 1,500 light years away, white Deneb is one of the most massive stars in the universe, a super-giant more than 20 times the size of our sun and shining 60,000 times brighter. Were Deneb our closest stellar neighbor, a mere 4.2 light years away like Alpha-Centauri, it would cast enough light on earth to read any time of day or night.

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