The Milky Way over Tucson

Alan Strauss, an amateur astronomer and director of the UA Sky School and Mount Lemmon Sky Center, usually captures images of the Milky Way, such as this one.

With the moon out of the way for a few days, take time to enjoy one of the more famous constellations, Gemini the Twins.

It is large and bright and somewhat resembles what it is supposed to represent. At 9 p.m., Gemini is almost directly south and nearly overheard. The “twins” in Gemini are Castor and Pollux, the 23rd and the 17th brightest stars in the sky, respectively.

Castor is farther north and is white. Pollux is slightly brighter and is orange-red in color. Castor is one of the most marvelous stars in our sky. It is a famous “double star” used by amateur astronomers to test the optics of their telescopes. Through a telescope with good optics and sufficient magnification, Castor appears as two close, nearly equally bright stars. But there is much more. Each of these stars is in fact a close double star that cannot be resolved by ordinary telescopic means, and there is even more. There is a third fainter star that is part of the Castor system. This star is also a very close double star. Thus, Castor consists of three sets of twins traveling through space together orbiting around each other in a complex fashion.

Pollux is just as interesting as Castor. It has a giant planet orbiting it and is the brightest star currently known to have a planet.

Contact Tim Hunter at skyspy@Tucson.com