Ursa Major

The Great Bear and the Big Dipper

Ursa Major is the third largest constellation in the sky, but most people know only part of it. Seven bright stars form a ladle shape called the Big Dipper in North America and the Plough in Britain. In the full figure, the bowl is the bear's body and the handle its long tail.

The rest of the Bear, its head and legs, is made of fainter stars spreading toward Leo and Lynx. Five of the seven Dipper stars move together through space as a loose group called the Ursa Major Moving Group, about 80 light-years away.

How to find it

Look north. From mid-northern latitudes the Dipper circles Polaris once a day and stays above the horizon all night, all year. On spring evenings it rides high, almost overhead; in autumn it skims low over the northern horizon, and in winter it stands on its handle in the northeast.

Use it to hop to other stars. The two stars at the outer edge of the bowl, Dubhe and Merak, point to Polaris about 28 degrees away. Follow the curve of the handle away from the bowl to 'arc to Arcturus', the bright orange star of Boötes, then 'speed on to Spica' in Virgo. A line from the bowl's inner stars, Megrez and Phecda, leads south to Regulus in Leo.

Main stars and their names

The Dipper's stars carry Arabic names that describe parts of the bear. Dubhe means 'bear'. Merak comes from a word for 'loins' and Phecda from 'thigh'. Megrez, the faintest of the seven, means 'base of the tail'.

In the handle, Alioth is the brightest star of the constellation; the origin of its name is uncertain. Mizar means 'girdle' or 'apron', and its faint companion Alcor sits right beside it. At the tip, Alkaid comes from a phrase meaning 'leader of the mourners', from an Arabic image of a funeral procession following a bier.

Mizar was one of the first double stars ever seen in a telescope, and later work showed that both Mizar and Alcor are themselves multiple systems.

Deep-sky objects for binoculars and small telescopes

Draw a line from Phecda through Dubhe and extend it about the same distance again. There you find M81 and M82, two galaxies about 12 million light-years away. In binoculars M81 is an oval glow and M82 a thin streak; a small telescope shows M82's cigar shape, which is shaped by a burst of star formation.

M101, the Pinwheel Galaxy, sits above the handle near Mizar and Alkaid. It is large but faint, so it needs a dark sky. Below Merak, the Owl Nebula, M97, is a planetary nebula, a shell of gas thrown off by a dying star; it needs a telescope and patience.

Even without optics, Mizar and Alcor are a good test: people with normal eyesight can usually split them on a dark night.

Mythology

In the best known Greek story, Zeus loved the nymph Callisto. His wife Hera, or in some versions the goddess Artemis, turned her into a bear. Years later her son Arcas nearly hunted her, so Zeus put both into the sky as the Great Bear and the Little Bear. The bears' unusually long tails were explained by Zeus swinging them up by the tail.

Several Native American peoples also saw a bear in the bowl, with the handle stars as hunters chasing it. In much of Europe the seven stars were a wagon or a plough. Old Turkic peoples called them Yedigen or Yedi Han, 'the seven', and imagined them tied to Polaris, which they called Demir Kazık, 'the iron stake'.

Practical observing tips

Spring evenings are best, when the Dipper is high and far from the haze of the horizon. It is bright enough to see from cities, which makes it the ideal first pattern to learn and the best starting point for star hopping.

For the galaxies, wait for a moonless night and a site away from lights. Rest binoculars on something steady, find M81 and M82 first, and only then try fainter M101. Watch the Dipper over a few hours or seasons to see how the sky turns around Polaris.