3-D Swan
Cygnus, the swan, soars high overhead on summer nights. This beautiful star pattern really does resemble a swan, with a long, graceful neck and wide-spread wings. It's high in the east at nightfall.
The stick-figure pattern that forms the swan makes a two-dimensional picture against the dark sky. In fact, many cultures thought of the stars as holes in a dark curtain, or as lanterns affixed to the dome of the sky.
Today, though, we know that the stars form a three-dimensional pattern. The star that forms the swan's head is about 380 light-years away, while the one that connects the body with the wings is about 1500 light-years. And the swan's tail is at least that far, and perhaps as much as a thousand light-years farther.
Measuring the distances to stars is tough. The technique that astronomers use for measuring the closest stars is called parallax. They look at a star at six-month intervals, when Earth is on opposite sides of the Sun. It's like having two "eyes" that are about 185 million miles apart. Stars that are close to us appear to shift back and forth against the background of more-distant stars. Measuring that shift gives a precise distance to the nearby stars.
But Earth's atmosphere blurs a star's light, making it hard to pinpoint its precise location in the sky.
Still, astronomers managed to use this technique for the first time almost two centuries ago - on a star in Cygnus. More about that tomorrow.
Script by Damond Benningfield, Copyright 2005
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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