Ursa Major - The Great Bear

Ursa Major is the third largest constellation in the sky. It includes the seven stars which form the famous Big Dipper. It is a circumpolar constellation, meaning that it can be seen throughout the year for those in the northern hemisphere.

History and Mythology

Ursa Major has many associated myths. A North American native legend says that Ursa Major was a great star bear wounded in a hunt. Every fall, blood drips from the wound, coloring the Earth's forests red.

Another native American legend tell us that bears did not know how to keep warm in the winter and kept complaining to the Great Spirit. He taught them to make dens and go to sleep to keep warm. To teach other bears to prepare for winter, he put two bears in the sky close to the North Star. He caused the bears to move around the North Star so that for half of the year they are under it, and for the other half they are above it. When they are under the North Star, they are in their dens, and it is winter. When they are above the North Star, they are out of their dens, and it is summer.

The ancient Arabs knew this constellation as the Bier and Mourners, and its movement was compared with that of a funeral procession. The square was the coffin and the mourners were represented by the stars in the bear's tail.

Ursa Major was an important constellation in the Far East. The early Chinese worshipped Ursa Major. They still use the seven stars a common symbol in Chinese design. These stars are also used on ancient coins, mirrors, and in stone carvings.

British mythology has the Great Bear interwoven with stories of King Arthur and the Round Table. His name is said to come from the Welsh words for bear, "Arth" and the word for wonderful "Uthyr". The arc that the bear's tail makes each night was said to be the model for the Round Table. After his death, it was believed that Arthur's soul traveled again into the heavens where he could rule over the people of England, and Ursa Major became known as Arthur's Chariot.

Notable Stars

Alpha Ursae Majoris, or Dubhe, is the brightest star in Ursa Major, with a magnitude of 1.9. It is an orange giant. Beta Ursae Majoris, or Merak, is a white star 79 light years away. Dubhe and 2nd magnitude Merak are the pointer stars of the Big Dipper; a line through these stars points to Polaris, the North Star. The other two stars making up the bowl of the Big Dipper are Gamma and Delta Urase Majoris, traditionally named Phecda and Megrez.

The stars in the Dipper's handle are Epsilon, Zeta, and Eta Ursae Majoris, traditionally named Alioth, Mizar, and Alkaid. All of the Big Dipper's stars, except Alpha (Dubhe) and Eta (Alkaid), are similar to Sirius, and form a physically-related group moving together through space about 80 light years away. Alkaid and Dubhe are moving in different directions, ultimately dooming the Dipper's shape.

The third star in the handle of the Dipper is 2nd-magnitude Mizar. This is one of the most familiar double stars in the sky. Mizar has a 4th magnitude companion Alcor, which is visible to the naked eye; this was used as a test of visual acuity by the ancient Greeks. It is unclear whether Mizar and Alcor are related physically; they lie at different distances of 78 and 81 light years, respectively, but share the same common motion through space.

Mizar was the first double star to be discovered with a telescope. In a small telescope, it appears as two stars of magnitude 2.4 and 4.0 with a separation 14 arcseconds. Later observations with the spectroscope revealed that both components of Mizar are also doubles, too close to be resolved visually. Thus Mizar, with its four components, was also the first spectroscopic binary discovered.

Another faint double star in Ursa Major was mistakenly recorded by Charles Messier as a nebula. M 40 is one of the three "nonexistent" nebulae in Messier's catalog. Recent studies indicate that it is probably not a true binary star system either, but a chance alignment with one star passing between us and the other.

Iota Ursae Majoris was also named Dnoces ("second," spelled backwards) after Apollo astronaut Edward H. White II. The name was invented by his fellow astronaut Gus Grissom as a practical joke, but has endured as memorial to both astronauts, who perished in the 1967 Apollo 1 fire.

Xi Ursa Majoris was the first binary system discovered. It is relative nearby, 27 light years away, and contains two 4th-magnitude sunlike stars orbiting each other with a 60 year period. At their widest separation the stars are 3 arcseconds apart.

The dim, 8th magnitude red dwarf star Lalande 21185 is located in Ursa Major, about 8.2 light years away, and is the fourth-closest star system to our own. 47 Ursae Majoris is a sunlike 5th-magnitude star lying 46 light years away. In 1996, astronomers discovered a planetary system around 47 UMa similar to the configuration of Jupiter and Saturn in our solar system.

Clusters, Nebulae, and Galaxies

Although Ursa Major is marked by the Big Dipper, its area is much larger than that taken up by those seven stars, and contains many interesting deep sky objects as well. One of these, M 97, is known as the Owl Nebula. It is a large, dim planetary nebula best seen with a 12 inch or larger telescope. Two patches in the nebula suggest the eyes of an owl.

Ursa Major is rich in bright galaxies. M 81 is one of the most spectacular galaxies in the sky. It is an 8th magnitude spiral with wide dust lanes which stretch outward to the edge of the disk. M 81 appears as an elongated, diffuse patch in small telescopes. Larger telescopes reveal the spiral structure.

M 82 is a 9th magnitude neighbor of M 81. It is a peculiar galaxy with tendrils of material extending away from the nucleus, suggesting a colossal explosion. In small telescopes, M 82 is little more than an elongated blur.

The galaxy M 101 is a face-on spiral, located near the handle of the Big Dipper. It is bright, but relatively large, giving it a low surface brightness which can make it difficult to see in smaller telescopes.

Other noteworthy galaxies in Ursa Major include the 10th-magnitude barred spirals M 108 and M 109, at 45 and 84 million light years away, respectively; and the 10th magnitude spirals NGC 2841 and NGC 3184, at 46 and 25 million light years away