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NGC 6656

At a distance of some 10,600 light years, M22 is among the nearest globular clusters to the Solar System. It lies within the plane of the Milky Way in the approximate direction of the Galaxy's core. In the skies of Earth, it falls within the constellation Sagittarius, close the group of stars commonly known as the Milk Dipper. M22 is close enough that its globular shape covers an area of the sky comparable with that of the Moon's disc, but intervening galactic dust makes it far less bright in the sky than it would otherwise be: the cluster has a visual magnitude of +5.5, on the edge of naked eye visibility.

The cluster itself contains nearly 100,000 stars, densely packed into a spherical region nearly a hundred light years in diameter. This is an unusual globular cluster in many respects, apart from its size (which is rather larger than most clusters of its kind) it is also home to at least one planetary nebula, and also to a number of black holes - rare phenomena to be found within a globular cluster.


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