Much of Ursa Minor lies in the cradle of Draco. It is bordered by Cepheus, Camelopardalis, and Draco. For northern observers, it can be seen year around. Ursa Minor is the home of Polaris, the North Star or the Pole Star, and the famous Little Dipper.
History and Mythology
Ursa Minor dates from the Greek philosopher Thales in the 6th century BC. Mythology says that the Great Bear (Ursa Major) was once a woman named Callisto. Zeus, the Greek god, fell in love with her. His jealous wife turned the woman into a bear. Arcus, her son, met the bear in the woods. Not knowing it was his mother, he aimed his bow and arrow at her. Zeus turned Arcus into a little bear to save Callisto. He grabbed both bears by their tails and pulled them into the heavens. The large bear is Callisto, the small bear is Arcus. And because he pulled so hard, their tails were stretched.
Notable Objects
Ursa Minor's main interest is the star Polaris, or Alpha Ursae Minoris. It is both a double and variable star. The primary is a classic Cepheid variable, of magnitude 2.1 to 2.2, with a period of four days. It is a yellow white supergiant lying 430 light years away, and has a pale white 9th-magnitude secondary appearing 18.6 arcseconds away.
Polaris is commonly called the North Star or the Pole Star because it lies about 1/2 degree from the North Celestial Pole. As the Earth rotates, the sky appears to rotate in the opposite direction. Since Polaris is near the center of the rotation, it stays in almost the same position in the sky, while the other stars circle around it. Polaris' fixed point in the sky makes an invaluable reference point for navigators.
Due to the precession of the Earth's axis, the exact location of the north celestial pole slowly moves, completing a cycle every 26,000 years. Due to this motion, Polaris was more than 4 degrees from the pole at the time of Copernicus and Columbus; in fact, it will be closest in the year 2110. At much more distant times in the past and future, other stars have been closer to the pole star. For example, around the time the pyramids were built, in 4000 BC, the closest star to the pole as Thuban, in Draco. Around 10,000 BC Vega was the pole star; it will be again around 14,500 AD.
Kochab and Pherkad (Beta and Gamma Ursae Minoris) make up a small asterism called the "Guardians of the Pole." They served as twin pole stars from 1500 B.C. until 500 A.D., although neither star was as close to the pole as Polaris is now. Kochab is an orange giant star at a distance of 126 light years; Pherkad is a hot white giant star, with a distance of 480 light years.
There are no prominent star clusters or nebulae in this constellation.