Constellation Data

Name: URSA MAJOR Translation: Big Bear Abbreviation: UMa Genitive: Ursae Majoris Size: 3 Regions: Circumpolar RA: 11 hours Decl: +50 degrees Season: Anytime Spring Midnight Culmination: March 11 Pages where URSA MAJOR is discussed in Chet Raymo's 365 Starry Nights: 77-83

What is the Genitive form? What is Right Ascension (RA)? Is this constellation ever visible from my latitude? What is Declination? Where should I look for a constellation on a date before or after its midnight culmination? What is Midnight Culmination?

Skylore

Only the most imaginative can see a bear in the area of the Big Dipper. There are many star-patterns that look like dippers, triangles, or squares in the sky. There are very few that actually resemble bears or people. Yet constellations were named to honor particular figures in ancient stories, not because the star pattern actually looked like the figure being honored. It took imagination to invent them a long time ago, and it takes imagination to see them now.

The "handles" of the dippers represent the "tails" of the bears on ancient star maps--even though modern bears don't have long tails! The Big Bear was regarded as a bear before Homer, and an ancient Greek story explains why the Big and Little Bears have such long tails.

A long time ago, Zeus fell in love with a mortal woman named Callisto, who was a far-traveler and a huntress. In jealousy Hera, the wife of Zeus, changed Callisto into a large bear. In a forest one day, Callisto's son Arcas chanced upon a huge bear. To his horror, the bear immediately started to run straight toward him. Not perceiving that the bear was his mother, Arcas raised his javelin to slay the bear. Zeus saw the tragedy that was about to happen, but not even Zeus could undo the spell of Hera. The only alternative was to change Arcas into a bear like Callisto, only smaller. To keep them safely together, and to make them immortal, Zeus grabbed both bears by their tails, swung them around and around, and hurled them into the sky. So much swinging stretched out their tails. Yet Hera had the last word, moving them to the part of the sky which never sets. There Callisto and Arcas now endure a weariness without rest until the end of the world.

(Adapted from Ovid's Metamorphoses)

Description

Ursa Major or the Big Bear is the third largest of the 88 constellations. Seven stars form a familiar group of stars, or an "asterism" within the constellation. In America they are called the "Big Dipper" or "Drinking Gourd," and in Britain the "Plough" or the "Wain." The Big Dipper is one of the most easily recognizable groups of stars in the sky. It is referred to as circumpolar because it never completely sets below the horizon, but is visible in northern skies year-round.

Three stars make up the Big Dipper's handle, and four stars make its bowl.

If you can find the Big Dipper in the sky, you have a skymark to orient yourself both on the Earth and in the Heavens. The two stars that form the pouring side of the bowl point to Polaris, the north star. Polaris is a rather faint star about five times farther away than the distance between the pointers themselves, and marks the tip of the handle of the Little Dipper.

The Big and Little Dippers pour into each other, just as the Big Bear and the Little Bear ceaselessly turn around and around the northern sky. The Guard stars of the Little Dipper protect Polaris from the Great Bear, just in case he might try to catch the North Star for himself.

Legend: In the constellation chart above...
• Star colors represent their spectral types (even for double stars).
• Bright star labels are yellow; significant other stars are labelled in magenta.
• The size of each star indicates its relative magnitude.
• Constellation names are light blue.
• Grid lines represent either 10 degree intervals of declination above or below the equator, or intervals of one hour (=15 degrees) of right ascension (measured along the equator).
• Messier object numbers are pink.
• Galaxies are ovals: blue if spiral, yellow if elliptical, light blue if irregular.
• Globular clusters are gold starbursts.
• Open clusters are dotted white circles.
• Planetary nebula are green diamonds.
• Bright nebula are magenta squares.
• Dark nebula are grey rectangles.
• Green x's are x-ray sources.
• Purple O's with a diagonal slash through them are quasars.

Asterisms

Big Dipper

Pointers

What is an Asterism?

Special Stars

Look at the second star from the end of the dipper's handle. Look closely, and you may see two stars, Alcor and Mizar (Migh-zar), which are also known as the Horse and Rider. According to the Greeks, the second star is one of the Pleiades sisters, who left her six sisters in the constellation Taurus (TORE-us) when she married. Mizar, the brightest of the two, is visible as a double star in a large telescope. Interestingly, from spectroscopic evidence it is known that both components of Mizar are each double stars as well, so that there are actually four stars in Mizar, which along with Alcor make five stars in this single system.

Table of 25 Brightest Stars.
What is apparent stellar magnitude?

Nebulae

M97, Owl Nebula (Planetary nebula), mag. 11.1.

What are Nebulae?
Table of Messier Objects.
What is apparent Magnitude?

Galaxies

M81 (Spiral galaxy), mag. 7.0.

M82, Exploding Galaxy (Irregular galaxy), mag. 8.4.

M101 (Spiral galaxy), mag. 7.9.

M108 (Spiral galaxy), mag. 10.5.

M109 (Spiral galaxy), mag. 10.0.

In the area of Ursa Major near the Big Dipper are two remarkable galaxies, both of which are too far away to view without a telescope.

• M81 is a classic spiral galaxy we see almost face-on, about the same size as the Milky Way, beautiful in its graceful repose.
• In contrast, M82, seen edge-on, may have experienced a titanic explosion. No one knows for sure, but M81 and M82 are wrapped in a common envelope of dust. Perhaps the passing of M81, which is almost ten times larger, has left the smaller M82 disrupted in its wake.

For ten days in December of 1995 the Hubble Space Telescope collected light from a blank spot of sky, devoid of naked-eye stars, just above the bowl of the Big Dipper. This project, known as the Hubble Deep Field survey, covered an area of the sky about one-twenty-fourth of a degree wide, no larger than a grain of sand held at arm's length. Within this tiny spot of sky, beyond the reach of earth-bound telescopes, were brought into view over fifteen-hundred galaxies, four billion times fainter than the limits of human vision. This snapshot of the Big Bang's galactic baby boom discloses galaxies in an astonishing plenitude and variety. There are spirals and ellipticals and bar-shaped galaxies, the same familiar galactic types seen in galaxies nearer to us. Many are colliding, some interacting or exchanging their material. Many are seen edge-on; many face-on; and many from every angle in between. Their stars are colored blue, yellow, and orange. Their light has travelled to us across eons of time from the remotest parts of the known universe.

What are Galaxies?
Table of Messier Objects.
What is apparent Magnitude?

Discussed in these Shows

• Stars of Our Neighborhood
• Cowboy Astronomer
• Follow the Drinking Gourd
• Starstruck Tonight

©1997 Welcome to the Basic Celestial Phenomena web site. To provide explanations of basic observational astronomy to students, teachers, families, and visitors to planetariums these pages have been written by an ex-OBU Planetarium Director, Kerry Magruder; the OBU Natural Sciences Coordinator, Mike Keas; and some of the students who work in the OBU planetarium.

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