Sunday, September 5, 2021

The Big Dipper

If you ask someone to name you a constellation they will most likely point you to the Big Dipper.

Known since ancient times, the Big Dipper is so easily recognizable due to the seven stars that make it up, much brighter than the surrounding ones.

The Big Dipper, however, is not a constellation, but an asterism. In fact, this term refers to any group of stars that is recognized in the sky for its geometric arrangement, but which does not fall within the 88 constellations. The Big Dipper is in fact part of the constellation Ursa Major, of which it forms the tail.

Both the constellations and the asterisms obviously have no physical meaning: in most cases the stars are in fact very far from them. If they appear to be arranged in the shape of some object or animal, such as a bear, it is only because we are unable to recognize the depth of the celestial vault with the naked eye.

It's easy to see this by comparing the distances of the seven stars of the Big Dipper: the closest, Megrez, is 58 light-years away, while the farthest, Dubhe, is 124 light-years from Earth.

Credit: Miguel Claro.

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