Ursa Major, the Great Bear, is one of the most well-known constellations in the sky, and with good reason. Its seven brightest stars form a pattern that’s familiar to people across the world as the Big Dipper, the Plough, or by multitude of other names. As an added bonus, these seven stars can be used to find other bright stars and constellations, making them the equivalent of a celestial signpost in the sky.
Ursa Major’s seven brightest stars are so well-known that it would be impossible to discuss every myth and legend associated with the constellation. We inherited a little more than half the constellations we know today from the ancient Greeks, with Ursa Major being one of them. However, many other cultures across the world also saw these stars as representing a bear.
The often-told Greek legend involves Callisto, a sea nymph, who was seduced by Zeus and bore him a son, Arcas. Hera, the long-suffering wife of Zeus, was infuriated, and in an act of vengeance, turned Callisto into a bear.
Years passed, and Arcas was hunting in the woods when he came across the bear. Not knowing it was his mother, he was about to kill the animal when Zeus intervened. To save Callisto’s life, he threw her into the sky, where she became Ursa Major, the Great Bear. Similarly, Arcas was transformed into a smaller bear, Ursa Minor, before also being thrown into the sky beside his mother.
(Incidentally, both Ursa Major and Ursa Minor have unusually long tails, which is explained by the fact that Zeus flung them both into the sky by their tails, causing them to be stretched in the process!)
Ursa Major’s tail is marked by three stars: Alkaid, Mizar and Alioth. To the Inuit people, these were three hunters who would chase the bear across the sky. In ancient China, the seven stars of the Big Dipper were seen as the throne of Shàngdì, the supreme deity, while many observers in Europe saw the stars as representing a chariot.
Many non-astronomers think the Big Dipper is the whole constellation, but that’s not actually the case. Those seven stars may be the brightest, but they only form the hindquarters of the bear. The rest of its body, plus its head, legs and paws, are all marked by much fainter stars.
Unless you live under rural or semi-rural skies, you may have some difficulty in seeing these fainter stars, but the seven stars of the dipper are easily seen from almost anywhere.
Starting at the very end of the dipper’s handle, we have Alkaid, then Mizar and then Alioth. The next star along is Megrez. It marks the point where the handle of the dipper attaches to the bowl, and, at magnitude 3.3, it is the faintest of the seven stars. Below that is Phecda, with Merak being the other star at the bottom of the dipper’s bowl. Lastly, we come to Dubhe, which marks the outside lip of the dipper’s bowl.
Merak and Dubhe share a famous connection, as many people also know them as “the Pointers.” That’s because if you draw a line from Merak, through Dubhe and keep going, you’ll come to Polaris, the Pole Star.
Draw a curved line through the handle of the dipper and you’ll come to Arcturus, a bright orange star in the kite-shaped constellation of Bootes, the Herdsman. Keep the curve going and you’ll come to Spica, the brightest star in the constellation Virgo, the Virgin.
Go back to the dipper and draw a line from Megrez and through Dubhe. Keep going and you’ll come to Capella, in Auriga, the Charioteer. A line north through Phecda and Megrez will lead you to the constellation of Draco, the Dragon, while a line in the opposite direction will take you to Leo, the Lion.
Lastly, draw a line from Megrez through Merak and you’ll arrive at Castor and Pollux, the two stars that mark the heads of Gemini, the Twins.
The dipper’s handle hides an added bonus that almost anyone can see. Look carefully at Mizar, the middle star of the handle, and you’ll see a tiny, much fainter star beside it. This second star is known as Alcor, and together the pair form the easiest double star in the entire night sky.
However, it gets even better. Turn a telescope toward Mizar and a low magnification of around 30x will be enough to split this star into two blue-white stars, making this a favorite with amateur astronomers of all ages.
Besides the Big Dipper and Mizar, Ursa Major is also home to a number of deep sky objects, including seven Messier objects: M40, M81, M82, M97, M101, M108 and M109. Five of these are galaxies.
Of these, M40 is the most lack-luster. Messier had described seeing some nebulosity here, but the fact of the matter is that no one has seen any nebulosity since, and this “deep sky object” is now known to be merely a double star.
There are several Messier objects in Ursa Major that may be considered challenging. M97, the Owl Nebula, is conveniently located just 2.3 degrees from Merak, but its light is scattered over a fairly large area, making it tricky to spot. Small scopes will show a dark, low contrast circular patch, but you’ll probably need an aperture of around 150mm to see the eyes of the owl.
The galaxy M108 is just 1.5 degrees from Merak and even though it’s reasonably bright, it’s also small and the light from nearby Merak can make the galaxy difficult to spot. It’s a similar story with M109, which lies only 38 arcseconds from Phecda and is easily drowned out by that star’s light.
M101, the Pinwheel Galaxy, forms a triangle with the stars Alkaid and Mizar, and can be found close to the border with Bootes. At magnitude 7.9, it’s bright enough to be detected with binoculars under a dark sky, but otherwise you’ll need a telescope of around 200mm and a filter to get the best view.
However, the deep sky highlight of Ursa Major is the galaxy pair of M81 and M82. Of the two, M81 (Bode’s Galaxy) is brighter and larger, and while M82 (the Cigar Galaxy) is fainter, its light is more condensed, which helps to increase its visibility. This pair is a favorite with astrophotographers, as they’ll both easily fit within the same low-powered field of view.
A small telescope will show M81 as a small, oval patch, while M82 appears as a streak. You might also notice some texture on M82, while a scope of around 400mm will show the dark, diagonal dust lane that effectively cuts the galaxy in two. M81 tells a similar story; there’s not much to see with a small scope, but an aperture of around 200mm (and averted vision) can help to show its spiral arms.