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November 10, 2010

As night rolls along, the stars roll with it. From the northern hemisphere, the stars appear to rotate around the North Star, Polaris. The stars aren’t actually moving. Instead, they roll across the sky because Earth is turning on its axis. They revolve around Polaris because the axis points in that direction.

Stars that appear especially close to Polaris remain above the horizon 24 hours a day -- they never rise or set.

An example is Capella, the brightest star of Auriga, the charioteer. From the far-northern United States -- places like Minneapolis or Seattle -- Capella never sets. And even from more southerly locales, it remains in the sky most of the time.

Capella’s one of the half-dozen brightest star systems in the night sky. It actually consists of two giant yellow stars. From their distance of more than 40 light-years, their light blurs together, forming a single pinpoint in the night sky.

Both of Capella’s stars are bigger and heavier than the Sun. And their classification as “giants” indicates not just that they’re big, but that they're late in life. They’ve used up most of the nuclear fuel in their cores, and they’re undergoing a series of changes as they near the ends of their lives. The Sun will go through similar changes in several billion years.

Capella is low in the northeast at nightfall, wheels high across the sky in the wee hours of the morning, and stands high in the west-northwest at first light.


Script by Damond Benningfield, Copyright 2003, 2007, 2010


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