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Asterisms and Constellations

Chris Steward of South Africa sent a comment on our Good Word constellation that I thought we all might benefit from:

I did not know that strew was related, though it makes poetic sense.

There are precisely 88 internationally-recognised modern constellations identified by the IAU, who have sole mandate for such naming.

There is another word, ‘asterism’, which denotes an “informal” constellation, i.e. a group of stars in some recognizable pattern named for convenience in discussion. There are a host of asterisms, as well as archaic constellations from various cultures (which I suppose are now asterisms, too, since their fall from grace).

An obvious asterism would be Orion’s belt, otherwise known as die drie konings “the three kings”. Also prominent and well known worldwide are the Pleides, known informally as “the Seven Sisters” (Subaru in Japanese) even though the cluster contains many more than seven stars. In the southern hemisphere, we have the constellation Crux (the famous Southern Cross), and the asterism of the False Cross (which neophytes typically confuse with Crux). These two can easily be distinguished by the fact that the asterism of “the Pointers” helps to highlight the true cross, whereas the false cross has no such neighbour. Another would be the Teapot, which is a subset of Sagittarius.

Some asterisms are too small or too faint to the naked eye for them to be commonly known, but are readily identified with optical assistance and many are well known in, um, the constellation of astronomical observers. The Coathanger is a prime example. There is even a beautiful triangle-within-a-triangle known as the “Stargate” (after the TV series).

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