The Texas Astronomical Society presents:

Constellation of the Month

by Rick Raasch


Ursa Major is one of the most well known constellations in the heavens. It contains the famous grouping of stars known as the Big Dipper, which is often the first group of stars learned by people in the northern hemisphere. Several other "firsts" are associated with this constellation; the star Mizar was the first double star to be discovered through a telescope (1662), the first star to be photographed (1857), and the first star to be identified as a spectroscopic binary (1889). Also, the star Xi UMa was the first binary star to have its orbit calculated (1828).

As Ursa Major lies away from the obscuring dust of the Milky Way, many galaxies are visible in its confines, and several of these are large and bright in amateur instruments due to their relative closeness. A whole night's observing can easily be spent in this large constellation.

M-81: This is a large and beautiful spiral galaxy, 10' long and 4' wide, oriented NNW-SSE. It has a bright core with a stellar nucleus, and spiral arms can be seen, especially with averted vision.

M-82: One of my favorite objects! This peculiar galaxy is 10'x2-3', oriented NE-SW. It has slightly tapering ends, and a great amount of mottling across its length can be seen. The southern edge appears flatter, and it seems to be "pinched" near the center on this side. Fascinating.

M-97: The Owl Nebula. This large planetary nebula is almost 3' in diameter, and appears as a gray puff of light, slightly brighter in the center. At times, especially with averted vision, the "eyes" of the owl can be seen as two slightly darker spots.

M-101: A large face-on spiral galaxy with low surface brightness. It is about 7' in diameter, with a brighter core surrounded by an envelope which sometimes can be seen to be spiral arms.

M-108: Large, about 10'x3' extended ENE-WSW. This galaxy has an evident central bulge, a stellar nucleus, and tapering ends. The western end appears to be tapered more than the eastern end, and dark markings are seen along its northern edge.

M-109: 8'x4', oriented ENE-WSW, with a faint stellar nucleus. Spiral arms can be seen leading to the north and south. NGC 2841 A very pretty galaxy. 7'x2-3', oriented NNE-SSW, with a sharply brighter core and stellar nucleus. Dark markings can be seen, especially east of the nucleus.

NGC 3079: Fascinating. 6'x2' with an obvious central bulge and extended N-S. Broadly concentrated to the center with pointed ends. At times, the ends appear curled: the north end to the west, and the south end to the east. Very pretty.

NGC 3631: Large and impressive, this galaxy is roughly circular and 5' in diameter. The core is about 1' in diameter and has a stellar nucleus. Averted vision shows arms spiralling from the north to the east.

For more information contact the Texas Astronomical Society at

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Texas Astronomical Society
P. O. Box 25162; Preston Station
Dallas, Texas 75225

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This page was last modified: Apr. 8, 1995