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Volume 14, Issue 41 ~ October 12 - October 18, 2006

Sky Watch

by J. Alex Knoll

From North to South

Polaris and Fomalhaut stand juxtaposed like sentries in the night

Sunset reveals Polaris shining due north midway between the horizon and the celestial zenith. The brightest star of the Little Dipper, Polaris is often presumed to be one of the brightest stars in the heavens. In fact, at magnitude 2, it ranks a mere 48, no surprise at some 430 light years away. A yellow supergiant, Polaris is 45 times the size of our sun and 2,500 times brighter, even though fusion has ceased so that this old star feeds upon itself.

Due south, a first-magnitude sentinel shines far from the light of any other bright stars. Amid the dim constellation Piscis Austrinus, the star Fomalhaut was one of four royal stars to the ancient Babylonians around 3,000bc. (The others are Regulus, Aldebaran and Antares.) Translating to mouth of the fish, Fomalhaut’s southern peak then coincided with winter solstice; today it peaks around mid-October.

This bluish-white, first-magnitude star is the 17th brightest, 14 times brighter than our sun and only 25 light years distant. Compared to our 4.5 billion-year-old sun, Fomalhaut is a relative newborn at 200 million years.

In the early 1980s, astronomers observing the infrared spectrum from Fomalhaut discovered a cool disk of stellar matter four times larger than our solar system encircling the star. Scientists believe that our own solar system formed from a similar stew of such ice, dust and cosmic matter.

Just last year, the Hubble Space Telescope observed a noticeable oblong ring extending far beyond Fomalhaut, strong evidence of at least one planet’s gravitational pull on the surrounding stellar debris. Still, even the Hubble cannot actually see a planet from a distant solar system; instead, physicists observe the effects of gravity on these stars’ orbits and light waves.

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