Guiding Light

StarDate: January 10, 2009

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If you're in Honolulu, Miami, New Orleans, or even here in Central Texas, look for the two brightest stars in the night sky scooting across the south late tonight. The brighter of the two is Sirius, and it stands high in the sky in late evening. The other is Canopus. It's well below Sirius, and a little to its right.

Canopus is one of the most important stars in the history of space exploration. Because it's so bright, and so far south in the sky, it was a key "roadsign" for early American spacecraft.

These craft used the stars for navigation. Locking on to the Sun and another star or two helped the craft keep themselves pointed in the right direction. That helped them aim their thrusters the right way, and make sure that their instruments were aiming toward the right body.

The Apollo astronauts used Canopus as a guide star, too. They had an onboard navigation computer, and they received tracking information from the ground. But they used a small telescope to sight on their guide stars to confirm that they were on the right path to the Moon, or back toward Earth.

While Canopus's far-southern location is good for spaceships, it's not so good for American skywatchers. While Sirius shines brightly across the whole country, the view of Canopus is limited to southerly latitudes. If you're farther north than about Los Angeles, Dallas, or Birmingham, then Canopus stays below the horizon -- and out of sight.

Script by Damond Benningfield, Copyright 2008

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