Ptolemy’s Cluster, NGC 6475

An Open Cluster in Scorpius

Image exposure:
30 minutes
Image size:
2.11º x 1.4º
Image date:

This beautiful open star cluster in Scorpius makes a fine sight, standing out like bright white beacons, contrasting against the dim starry background of one of the Milky Way’s inner spiral arms.

Open clusters are a group of fresh new stars which have been formed by a gravitational collapse of gas inside a molecular cloud, mostly consisting of hydrogen. The stars are bound together by common gravity but over the course of many years will gradually disperse.

M7 is about 980 light years away and appears close to the tail of Scorpius. Across its fifty light year radius it is known to possess about eighty loosely spaced stars, many of which are concentrated towards its centre. The cluster is about 200 million years old (that’s young!) and the stellar winds have blown away the residual gas cloud.

Also in the Picture

Towards the bottom is the faint globular cluster NGC 6453, nearly forty times further away at about 38,000 light years.

Towards the lower left you might spot what looks like a bright double star. The one on the left is a star but the one on the right is another globular cluster, NGC 6441, also estimated at about 38,000 light years distance.

The dark patches appear to be gaps in the star clouds but in reality they are dark nebulae, foreground clouds of gas which are not illuminated by emission or reflection, blocking the visibility of the stars behind them.

Location of M7 in the sky


◽ Skywatcher Esprit 120 Refractor telescope.
◽ With 0.77 reducer = 644 mm focal length @ f/5.4
◽ Skywatcher EQ6-R Pro mount.
◽ ZWO ASI 071 MC cooled imaging camera.
◽ Images © Roger Powell

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  1. This kind-of reminds me of the Seven Sisters.

    They used to keep me company way back when I used to run before dawn.

    The upper left dark patches resemble facial features . . . but then, almost everything does.

    Liked by 1 person

    1. Similar clusters in some respects but M7 is somewhat less bright, although theoretically still visible to the naked eye at a dark site.

      The greatest memory I have from my youth is of the easily recognisable Orion constellation, but it was upside-down then.

      I guess if my image were a bagel, you’d reach for the camera


      Liked by 1 person

    1. I think you are right – but I have my doubts about whether there are any advanced alien civilisations in our galaxy at this point in time to make such a decision to avoid us.


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