Albireo, March 18, 2015

The double star Albireo is one of the most celebrated telescopic sights in the sky.  This image was created from a series of ten 15-second exposures taken with the Cook Memorial Telescope at about 6:25 am on March 18, 2015.

A double star is a pair of stars that appear to be close together in the sky.  Some double stars are binary stars, a pair of stars orbiting a common center of gravity.

Even a small telescope or good binoculars will reveal Albireo's double nature.  Albireo provides a good opportunity to observe contrast in the color of stars.  The brighter star glows golden, while the fainter star has a sapphire blue color.

Albireo is actually a triple star, and all three are more massive than our Sun.  The blue star, Albireo B, has about three times the mass of our Sun.  It is blue because its surface is hotter than our Sun.  The golden star, Albireo A, is really a tightly-orbiting binary star, too close for our telescope to resolve the difference.  One is a cool red giant star with five times the mass of our Sun, and the other a hot blue star like Albireo B.

Albireo is located 430 lightyears from the Sun.  The close stars of Albireo A take 100 years to orbit each other.  Albireo B is so widely separated from Albireo A that it is not certain if they are locked into gravitational orbit.  If they are, they take at least 75,000 years to complete one orbit.

Albireo is located in the constellation Cygnus, and represents the head of the swan.  It is visible high in the evening sky in late summer and early fall.

Telescope: 16" Cook Memorial Telescope

Camera: Canon T3i at ISO 6400