Above the Twinkles
A skyful of twinkling stars is an inspiration to poets, musicians, and others. But twinkling isn't all that inspirational to astronomers. In fact, it's a downright nuisance, and astronomers try to lift their telescopes high enough to avoid it.
Stars twinkle because Earth's atmosphere bends their light. Different colors of light are bent at different angles, which is why twinkling stars flash different colors.
Twinkling also spreads out a star's light, turning the star from a sharp pinpoint to a fuzzy blob. That makes it hard to measure a star's position in the sky, which in turn makes it hard to measure its distance.
Astronomers measure the distances to nearby stars through a technique called parallax. It's like looking at something that's close to you through first one eye, then the other; the object appears to change position against the background of more-distant objects. In the case of stars, the two "eyes" are measurements made when Earth is on opposite sides of the Sun. Nearby stars appear to move a little compared to the background of more-distant stars.
But the motion is so small that the blurring effect of the atmosphere makes it hard to measure. The most accurate measurements of star distances have been made from space. Astronomers are using Hubble Space Telescope to make new measurements, which we'll talk about tomorrow. And ultimately, a satellite called SIM may measure the parallax of stars out to the edge of the galaxy.
Script by Damond Benningfield, Copyright 2005
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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