Big Bear or Big Dipper? You’ve probably heard both names before – but where do the two names come from? Quite simply, the Big Dipper or Sky Dipper is a part of the Big Dipper, formed by the seven brightest stars of the constellation, which form the trapezoidal dipper with the distinctive drawbar. The whole constellation of the Big Dipper, on the other hand, is even bigger by a few stars, but all of them are less bright than those of the Dipper. The celestial chariot is probably the best known constellation in the northern sky, easy to find because of its typical shape. And not only that: you can see the Big Dipper all year round, at any hour of the night.
Actual starry sky
Which constellations are high in Bavaria’s night sky this month??
The Great Bear never sets over Bavaria – it is a circumpolar constellation: It is so close to Polaris, around which the entire night sky seems to revolve, that it circles it once in 24 hours. For the Romans, the Big Dipper was called the "seven threshing oxen" for this reason Called: The seven brightest stars of the constellation move around the North Star like oxen around the harrow of a threshing machine. To herd these oxen is the task of the neighboring constellation Bear Keeper, who is therefore also called Ox Driver. In the north the Big Dipper touches the horizon, but always remains visible. But on autumn evenings he trots along deep in the north. Only in spring it gradually comes out again and climbs higher and higher up the southern sky, until in May it is already high in the zenith in the early evening, vertically above you. In summer he takes his leave again and retreats to the northwest in the first half of the night.
So spring is the best time to have a closer look at the constellation. Because almost everyone knows the Big Dipper – but do you know the whole Big Dipper? His head and legs shine far fainter than the seven stars of the chariot, but with practice you will easily recognize the giant bear: Its head points to the west, its tail (the wagon’s drawbar) to the east. Its fore and hind legs can be found in the south – like a row of radiating colons.
Starhopping to Polaris
Guide over the sky
With the help of the sky cart you can orientate yourself well in the sky. Approximately, to find the polar star: Extend the rear axis of the chariot, the line from the star Merak to Dubhe, about five times, and you will end up exactly at Polaris, the north celestial pole. In spring, the Big Dipper also guides you to the Spring Triangle: If you extend the last piece of the drawbar, you will come across a strikingly bright star with a reddish glow: Arcturus in the constellation of Bear’s Keeper.
The Great Bear of mythology
The Latin name Ursa Maior means Great Bear. In Greek mythology, the Great Bear was actually the nymph Callisto, from the retinue of Artemis, the goddess of the hunt. Zeus, the father of the gods, took a great liking to Callisto and tried to seduce her – by taking the form of her mistress Artemis. The feat succeeded and Callisto was also immediately pregnant. This, in turn, angered Artemis so much that she turned her companion into a bear. And as a bear, Callisto was almost killed by her son Arkas, who did not recognize his mother in animal form. This in turn pity Zeus: He also turned Arcas into a bear – the Little Bear (also: Little Dipper) – and moved both to the sky. And because he grabbed them by their tails and flung them to the stars, the tails of the Little Bear and the Big Dipper (the drawbars of the chariots, respectively) are also that long.
Apparent and real double stars
Mizar and Alkor
Even with the naked eye you can see a double star in the Big Dipper: Above the drawbar star Mizar you find the "little rider": the less bright star Alkor. You need sharp eyes, because Alkor is only twelve arcminutes away from Mizar – that’s why the pair is called "eye-checkers". But the two form only an apparent double star. In reality they are three light-years apart and have no physical relation to each other. But each of them belongs to a true multiple star whose individual components orbit each other: Alkor is a triple system, Mizar a quadruple system: even with binoculars you can resolve Mizar into two components: The two are 14.4 arcseconds apart. In light spectroscopic investigations it can be seen that each of these two components in turn consists of two single stars – a double-double star.
The Big Dipper also has a star cluster – but it is not as conspicuous as the Pleiades in Taurus: Five of the brightest stars of the Big Dipper – Merak, Phekda, Megrez, Alioth and Mizar – move with the same direction and speed through space and thus form a so-called motion cluster – a loose star cluster, hardly recognizable as a group, whose stars have the same origin. The Ursa Major Motion Cluster or Bear Stream is only 75 light years away from us. Not all stars of the cluster are found in the constellation of the Big Dipper – also Sirius in the winter constellation of the Big Dog probably belongs to the Bear Stream.
mist in the Great Bear
Are you equipped with good binoculars or a telescope? Then take a closer look at the Big Dipper. The constellation has some beautiful galactic and extragalactic objects to offer! The Big Dipper is far away from the Milky Way, outside the star forming areas. Therefore you can hardly discover young objects of our galaxy in this constellation. But there is a pretty planetary nebula to be found – which is only about 6.000 year old Owl Nebula (Messier object M97, NGC 3587).
Galaxies M81 and M82
The view to the Great Bear leads to the edge of our own galaxy – and beyond: Countless alien star systems can be seen in this constellation. We would like to present a few of the most beautiful ones here: Right next to the Owl Nebula you can find the galaxy M108 (NGC 3556). A very rewarding and even for amateurs easy object is the M81 galaxy group above the shoulders of the bear – twelve million light years away from us. It includes the galaxies M81 (NGC 3031), M82 (NGC 3034), NGC 3077, NGC 2976 and eight other smaller galaxies. M81 and M82 physically belong together – the two galaxies are interacting.
Faint bridges of intergalactic gas have been discovered between galaxies – presumably the star systems once collided. Discovered in 18. Century. M81 is one of the most beautiful spiral galaxies in the northern sky, very symmetrical with clearly visible spiral arms. Also the galaxy M101 (NGC 5457) is worth a try with the telescope. The so-called Wagon Wheel Galaxy is the brightest galaxy in a group of nine star systems. It is about 27 million light-years away and can be found above the foremost drawbar.
What you will not see, even with a better telescope, are countless other galaxies, located in the front part of the drawbar of the Big Dipper. Here is the Hubble Deep Field, which has been studied for years by the Hubble Space Telescope.