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September's Star of the Month: Epsilon Lyrae

On September evenings, the exceptionally brilliant star Vega of the constellation Lyra, the harp, stands high overhead. Residing at a distance of 25 light years, it shines 50 times brighter than our Sun. This beacon star guides you to our feature star, Epsilon Lyrae.

To save on neck strain, you might want to view this star from the comfort of a chaise longue. Simply aim your binoculars at Vega, and you can't miss the double star Epsilon Lyrae. Vega and Epsilon Lyrae easily occupy the same binocular field, with Epsilon appearing as two pinpoints of light. If your feet are pointing south, Epsilon appears left of Vega; however, if your feet are pointing north, Epsilon appears to Vega's right. The northern star is called Epsilon 1, and its southern counterpart goes by the name Epsilon 2. On a night that's clear and dark, people with exceptional eyesight can see this double star without optical aid.

A good small telescope shows that each of these stars is also a double, meaning Epsilon is a double-double, or a quadruple star. Whereas the double is very obvious through binoculars, observing the double-double through a telescope requires more scrutiny. The component doubles remain close together, and likely appear to touch one another. The two stars comprising Epsilon 1 are thought to have an orbital period of some 1200 years, whereas those of Epsilon 2 are thought to orbit each other in about 585 years.

The two stars that you see through binoculars, Epsilon 1 and Epsilon 2, are believed to be gravitationally bound as well. It's estimated that it takes hundreds of thousands, if not close to a million years for the pair to complete one revolution around its common center of gravity.

Epsilon Lyrae's distance from Earth is somewhere around 160 light years.

by Bruce McClure

Stars of the Month Page

September 2002 Feature: Harvest Moon