APOD: M7: Open Star Cluster in Scorpius (2016 Jul 13)

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APOD: M7: Open Star Cluster in Scorpius (2016 Jul 13)

Post by APOD Robot » Wed Jul 13, 2016 4:05 am

Image M7: Open Star Cluster in Scorpius

Explanation: M7 is one of the most prominent open clusters of stars on the sky. The cluster, dominated by bright blue stars, can be seen with the naked eye in a dark sky in the tail of the constellation of the Scorpion (Scorpius). M7 contains about 100 stars in total, is about 200 million years old, spans 25 light-years across, and lies about 1000 light-years away. The featured wide-angle image was taken near the city of Belo Horizonte in Brazil. The M7 star cluster has been known since ancient times, being noted by Ptolemy in the year 130 AD. Also visible are a dark dust cloud on the lower right, and, in the background, literally millions of unrelated stars towards the Galactic center.

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Re: APOD: M7: Open Star Cluster in Scorpius (2016 Jul 13)

Post by Ann » Wed Jul 13, 2016 9:46 am

M7 and M6. Photo: Akira Fuji.
Ah, the Ptolemy Cluster! :D It's too far south for me, but it looks great in photographs. Seemingly suspended above billions of yellow grains of sand, yellow stars in the bulge of the Milky Way, M7 looks like collection of blue sapphires surrounding one brilliant orange spessartite garnet. By contrast, the "sister cluster" of M7, M6, the Butterfly Cluster, is spreading its wings against a lot of dark dust.

It's interesting to compare M7 with the Pleiades. There are interesting similarities, but the Pleiades are a little brighter and bluer. There are several B-type stars in M7, but most of them are spectral type B8 and B9, whereas the brightest stars in the Pleiades are about spectral class B6 and B7. But there is a star in M7, HD 162374, which is classified as a B6 star and is described as a blue straggler by Bright Star Catalog. Fascinating! Blue stragglers are thought to form when a main sequence star gains extra mass somehow and remains on the main sequence, or remains higher up on the main sequence, than the other stars of the same age and mass. I guess the blue star of Algol can be considered a blue straggler.

The bright stars of the Pleiades are brighter than the bright stars of M7, about 300-400 times solar or so versus about 150-300 times solar for M7. But the difference isn't great. The biggest difference is the presence of red giants in M7. Of course, there is a prominent red giant in M6, too.

When Alcyone, brightest star of the Pleiades, turns into a red giant, then the Pleiades might look somewhat like M7 or M6. Particularly since the Pleiades has most likely shed its lovely blue reflection nebula.

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Re: APOD: M7: Open Star Cluster in Scorpius (2016 Jul 13)

Post by Fred the Cat » Wed Jul 13, 2016 9:17 pm

If a group of stars is called a cluster what's a group of scorpions called?
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Re: APOD: M7: Open Star Cluster in Scorpius (2016 Jul 13)

Post by Boomer12k » Wed Jul 13, 2016 9:30 pm

"The Rock Concert" Cluster.... as the dark nebula is a "guitarist" on his knees with his arms raised up, after doing an awesome "riff"....

And all the stars are "on stage"....

I am moving, sold the house, after I move, I won't be able to get out my 10" Meade... me sad... new place is a wooded area, and doesn't have storage for it.... Mobile home park... If my deal falls though, I will be moving to a friends place temporarily... and then search for another place... sigh....

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Re: APOD: M7: Open Star Cluster in Scorpius (2016 Jul 13)

Post by Ann » Fri Jul 15, 2016 6:25 pm

Boomer12k wrote:"The Rock Concert" Cluster.... as the dark nebula is a "guitarist" on his knees with his arms raised up, after doing an awesome "riff"....

And all the stars are "on stage"....

I am moving, sold the house, after I move, I won't be able to get out my 10" Meade... me sad... new place is a wooded area, and doesn't have storage for it.... Mobile home park... If my deal falls though, I will be moving to a friends place temporarily... and then search for another place... sigh....

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I'm sorry to hear that, Boomer. Best of luck for the future. Keep posting here, you hear?

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Re: APOD: M7: Open Star Cluster in Scorpius (2016 Jul 13)

Post by Ann » Fri Jul 15, 2016 6:26 pm

Fred the Cat wrote:If a group of stars is called a cluster what's a group of scorpions called?
A bed of scorpions... no thanks!!!! :ohno:

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