The Many Faces of the Big Dipper

The stars of the Big Dipper are easy to spot.
Big Dipper

Without a doubt, in the Northern Hemisphere, the group of stars known as the Big Dipper is the most often and easily recognized. Not everyone saw it as a giant celestial dipper and there is a myriad of stories about this group of stars.

While it's so commonly recognized by folks, a large percentage of those same folks mistakingly refer to these stars as a constellation. In fact, the Big Dipper is an asterism, part of the constellation called Ursa Major. An asterism is a commonly recognized group of stars. The Southern Cross is another asterism, as is the backwards question mark in Leo and the teapot in Sagittarius.

The constellation Ursa Major is the “greater bear” and many stories surround it from all over the world. Ursa Minor, is the “lesser bear” and is made up of the group of stars which include the Little Dipper.

The bowl of the Big Dipper make up the middle body area of the bear. Dimmer stars make up the head and legs. Oddly, the bright stars which are the handle of the dipper, are supposed to represent a long celestial tail on our bear. But not everyone saw this long tail and one of the more interesting stories comes from the Algonquin Indians of the northeast US. The story also offers an explanation for the vivid fall colours of leaves, something the northeast is known for.

These are the stars of the constellation Ursa Major.
Constellation

Our story begins a long, long time ago. It features a really large and viscous bear, one with a real attitude problem and clearly no social graces. This bear spent his days going from village to village, trashing the place an killing many people. Everyone loathed the bear and may hunters tried to kill him but no one succeeded.

Finally, the people became so desperate that they searched the entire world and assembled the best hunters they could find. These hunters were promised much wealth if they could hunt down the bear. Soon after: the hunt began, and soon they found the bear. Being no fool, when the bear realized the talents assembled to exact revenge, he did the smart thing – he ran.

The hunters chased the bear for days and weeks and finally in desperation, the bear ran up into the sky. He is represented by the four bright stars in the bowl of the dipper. But the hunters also followed the bear up into the sky, and they are represented by the stars in the handle of the dipper. Finally, one of the hunters wounds the bear with an arrow and every autumn, a few drops of blood drip down from the bear's wound and colour the leaves.

Ursa Major
Ursa Major

There is a Hindu story about the Big Dipper which has different characters represented by the stars. According to this story, which dates back to about 500 BC, the stars of the Big dipper depicted the seven sages called Rishis. These sages were very important because the controlled the motions of the Sun, causing it to rise and set every day. The Rishis were married to seven sisters named Krttika. At one time they all lived contentedly in the north sky.

Then one day the Rishis were burning an offering and Agni, the god of fire emerged from the flames and immediately fell in love with all seven Krttika. Agni did not believe the Krttika would ever leave their husbands and so he went back to Earth and tried to forget them. One day he wandered into the forest where happened to live Svaha, who happened to have the hots for Agni. Svaha is represented by the star Zeta Tauri in Taurus.

These are the stars of the constellation Ursa Major.
Whirlpool Galaxy

Previously Agni had shown no interest for Svaha and so she knew she would have to resort to some devious method to obtain Agni's love. Fortunatly for Svaha, gossip was as popular then as it is now and she soon learned about Agnis trip to the Rishis and his love for the Krttika.

Possessing magical powers, Svaha disguised herself as six of the Krttika. Apparently the seventh Krttika, named Arundhati, could not be mimicked because her love for her husband was too great. Agni however, was beyond pleased to think that he had attracted six of the women.

Time passes and eventually Svaha gives birth to a child whom she named Skanda. Now new rumors began to spread that the mothers of the child were six of the Rishis wives. The Rishis were outraged, and immediately divorced their wives, all except for the Rishi married to Arundhati, who is represented by the star Alcor. The other six wives wandered the skies and eventually became the Pleiades.

Mizar and Alcor

If you look at the handle of the Big Dipper and find the second star from the end of the handle, you will have found a star named Mizar. Mizar is close as stars go, about seventy-five light years away. Now take a closer look at Mizar, and if you have good vision and dark skies, you will see Mizar has a companion: Alcor.

Several Native American tribes refer to Mizar and Alcor as the horse and rider and use them as a sort of celestial vision test for their warriors. Other tribes expand on the Algonquin story and say that Alcor is a pot the hunters are taking along with which to cook the bear!

The really interesting thing about Mizar and Alcor is that they are part of a system of not two stars, but six. Three of the stars are part of the Mizar system. Only one is visible by using binoculars or a telescope. The other two are so faint they can be detected only by the gravitational effect on the other two stars.

Alcor is part of a binary system. The companion is very faint and, like two of the stars with Mizar, can only be detected by its gravitational pull on Alcor.

Pointing the way to the north star

Hubble also produced this image of M81.
M81

The Big Dipper serves another useful purpose besides providing a vision test: it is an aid to finding the north star, Polaris. Many people think the north star is very bright and easy to find but that is not so. Polaris is, in fact, fairly dim but it is useful for both locating north and also your latitude. Polaris' height above the horizon is roughly equal to the observer's latitude.

To use the Big Dipper to locate Polaris we use the two outside stars in the bowl of the dipper, Dubhe and Merak, called the pointer stars. If you extend a line from Merak through Dubhe it will point to Polaris. Extend the line about five times the distance between Merak and Dubhe.

The Ursa Major Cluster

The Ursa Major Cluster is a group of about twenty stars, all moving together through space at an average distance of about seventy-five light years from the Sun.

Many of the stars in the Ursa Major Cluster are blue-white or blue Main Sequence stars. The notable exception to this is Dubhe. Dubhe is a yellow giant star and about one hundred ten times the brightness of our Sun.

Dubhe has another distinction: along with Alkaid, the star at the tip of the Big Dipper's handle, they are the only stars in the Big Dipper not associated with the Ursa Major Cluster.

Jewels for a telescope

If you happen to own a telescope Ursa Major provides numerous celestial objects but there are three especially beautiful to look at. The Messier objects M81 and M82 are located near Dubhe and are two of the brightest galaxies in the night sky. To locate them, extend a line about ten degrees from Phecda through Dubhe.

M82 imaged by Hubble.
M82
Details of M82 from Hubble.
M82

M81 is a beautiful spiral galaxy with distinctive unfurling spiral arms. M82 is classified as an irregular galaxy. Both galaxies are part of a small group of galaxies about ten million light years from Earth.

The third target is the magnificent Whirlpool Galaxy, M51. It is located about three and a half degrees southwest of Alkaid. M51 is about thirty five million light years from Earth and is classified as a spiral galaxy.

Ursa Major provides rich legends from cultures all over the world. It points the way to the north star and is very often the first constellation sky observers new to astronomy pick out. With its multitude of targets for binoculars and telescopes, Ursa Major is truly worth becoming familiar with.