August 5, 2008

In Today's One Minute Astronomer...

Albireo - A Spectacular Double Star

The bright double star Albireo that marks the head of Cygnus the Swan is a stunning example of contrasting colors and one of the finest double stars in the heavens. And today, a bonus object...

The Basics

• Albireo lies in the middle of the Summer Triangle formed by Vega, Deneb, and Altair. You'll have no trouble seeing it with the naked-eye as a single moderately-bright star, even in city skies

• In nearly any telescope, even at low magnification, Albireo resolves into a double star. The 3rd magnitude component shines a golden-yellow; the fainter 5th magnitude component is a sapphire-blue. The color contrast is striking… this is one of the most beautiful double stars anywhere in the sky.

• To observe Albireo, use low magnification since the colors stand out better when the stars appear closer together.

• If you have trouble seeing the colors, that's because your eye is less sensitive to color concentrated in tiny bright points of light. Try de-focusing your telescope just a little to smudge out the image. The color should become obvious.

Albireo, double-star at the head of Cygnus

A Deeper Look

• At one time, this pair was considered an optical double… just a chance alignment of two unrelated stars. However, in spite of the large distance between them, astronomers proved Albireo forms a true binary system that revolves about each other.

• At a distance of 385 light years from the Earth, this pair is physically separated by 60 times the diameter of our solar system. Although they revolve around each other, no orbital motion has been detected since Albireo was first measured in 1832.

Good To Know

In 1976, the brighter component of Albireo was itself resolved as a binary star using large telescopes and a complex image processing technique known as speckle interferometry. The separation of this close pair is only 0.4”, nearly resolvable visually with a 20-inch telescope. But to my knowledge, no one has visually resolved this star.

Bonus Object

A bonus object: try to find the “Coathanger” cluster, between Albireo and the small constellation Sagitta, the Arrow. Although not a true star cluster-- the stars are not physically associated-this asterism looks like an upside-down coathanger… very striking. Use low power with your telescope, or try binoculars.

--- Highly Recommended ---

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