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Delta Lyrae

StarDate: 
June 25, 2016

Although all the stars in the night look a lot alike, they actually glow in different colors. And tonight you can look for a pair of stars that makes a stunning color contrast. One star is blue, and the other is red.

This duo is known as Delta Lyrae, and all you need to see it is a pair of binoculars.

The different colors indicate that the stars have different surface temperatures. The blue star is hotter than the Sun, whereas the red star is cooler than the Sun.

The two stars aren’t a true binary — they’re not connected with each other in any way. They just happen to line up in the same direction from Earth.

The hot blue star is the more distant of the two — a bit more than a thousand light-years. It’s part of a small cluster of young stars.

The red star was once blue, too. But it used up the hydrogen in its core, causing its outer layers to expand. An expanding gas gets cooler, so the star’s surface went from being hot and blue to cool and red. The star is now a red giant, so it’s much bigger, brighter, and cooler than the Sun.

These colorful stars reside in the constellation Lyra, the harp. It’s easy to find because it’s home to Vega, one of the brightest stars in the night sky. It’s about half-way up the eastern sky at nightfall. Delta Lyrae is not far to the lower right of Vega, at the left point of a small diamond of stars. When you observe it through binoculars, you’ll see a lovely pair of stars: one blue, the other red.

Script by Ken Croswell, Copyright 2016

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