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M46 and M47

February 26, 2011

On a February night in 1771, comet hunter Charles Messier was scanning to the east of Sirius, the brightest star in the night sky, when he discovered two star clusters. One was small and faint, while the other was larger and contained more bright stars. Messier added them to his list of objects that might be mistaken for comets. And today, the clusters are still best known by Messier's catalog numbers: M46 and M47.

The clusters are in good view this evening, not far to the left or lower left of Sirius, which is well up in the southern sky as darkness falls.

Under dark skies, well away from city lights, M47 is just visible as a hazy patch of light a little smaller than the full Moon. But you really need binoculars to get a good view of both clusters.

M47 contains several dozen stars, including some that are red giants -- old, bloated stars that are in the final stages of life. Such stars are quite bright, which is one reason that M47 is prominent in our sky. Another is that it's fairly close as clusters go -- about 1600 light-years.

M46 is about three times farther, so it doesn't look as impressive. In fact, though, it contains several hundred stars, including several that are quite hot and bright. Such stars burn out fairly quickly, so their presence tells us that the cluster is only a few hundred million years old.

So scan the sky not far to the left of Sirius for M46 and M47 -- two great families of stars.


Script by Damond Benningfield, Copyright 2010


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