APOD: M7: Open Star Cluster in Scorpius (2012 Sep 12)

[APOD Robot]

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 above deep exposure was taken from Hakos Farm in Namibia. 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 and literally millions of unrelated stars towards the Galactic center.

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[Boomer12k]

Lower right....Man with a pickaxe???? The Miner Nebula???

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[Boomer12k]

Oooooo...Blue stars!

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[Ann]

Oooooo...Blue stars!

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Yessss!!!!

Ann

[Doc in SF]

Concerning: star clusters
There are many recent photos of various clusters. When I look closely at them, the background looks like a wall of solid pellets or bee-bees. What am I actually looking and why are the pellets various shades of dark gray?
Thanks
Doc

[ta152h0]

in my formwer profession, it required three views to describe and object and auxiliary views to completely describe it with associated wording. A picture on a flat sheet does not complete justice. really want to exercise your mind ? Every star in that image is seen from a point source, namely a human being on the earth and none of those stars are seen real time. The big Poobah in the Sky is toying with us !

[Boomer12k]

Concerning: star clusters
There are many recent photos of various clusters. When I look closely at them, the background looks like a wall of solid pellets or bee-bees. What am I actually looking and why are the pellets various shades of dark gray?
Thanks
Doc

If I understand your question, you are looking at a "wall of stars". They APPEAR close together as they are in a section of the sky with the Milky Way. (Some star clusters more or less.) The "edge on view" of our galaxy from the inside, our point of view from Earth. Find a view of the Milky Way on the web. Websearch, Images of the Milky Way. You can see many Star Clusters, Stars, Nebula and such, allot of them are within what we see as the "edge on view" towards the center of our galaxy. Not so much if you look toward the "top or bottom" of the galaxy. SO...if a star cluster was in a different portion of the sky...less stars...also photographic exposure will show more stars.
Hope I covered that.

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[rstevenson]

Concerning: star clusters
There are many recent photos of various clusters. When I look closely at them, the background looks like a wall of solid pellets or bee-bees. What am I actually looking and why are the pellets various shades of dark gray?

To quote the last sentence of the description of today's APOD...

literally millions of unrelated stars towards the Galactic center.

So those "pellets" are all stars themselves. Extraodinary, I know!

As for their colour, I'd say they only appear gray on average. Here's a blowup of a small portion of the image. You can see they are white and yellow and orange and blue, and they just seem to add up to gray as our eyes scan over them.

pellets.jpg (26.39 KiB) Viewed 3727 times

Rob

[Chris Peterson]

in my formwer profession, it required three views to describe and object and auxiliary views to completely describe it with associated wording. A picture on a flat sheet does not complete justice. really want to exercise your mind ? Every star in that image is seen from a point source, namely a human being on the earth and none of those stars are seen real time. The big Poobah in the Sky is toying with us !

We certainly aren't getting a good 3D image of the cluster, but I disagree that we aren't seeing the stars in "real time" in any meaningful sense.

[Ann]

Thanks, Rob, for your blowup of the background stars!

Today's APOD is a great portrait of a remarkable and beautiful open cluster. I was very glad to see it.

The links in the caption of today's APOD are great, too. Small tidbit here: M7, the cluster featured in today's APOD, may be the same age as magnificent M11.

I feel like giving everyone an open cluster salute. May the stars be with you!

Ann

[Glenriven]

The cluster is nice, but all those itty bitty stars behind them is amazing. With all the city light, it is easy to forget about them.

[dlw]

Can someone explain a bit more about open cluster formation? I'm puzzled by the 25 LY span. It seems quite a distance over which such a huge coordinated cataclysm could occur. 200 million years would seem a relative blink of the cosmic eye. Could cluster formation occur within a smaller region and then the resulting stars move apart 25 LYs within 200 MYs?

[Chris Peterson]

Can someone explain a bit more about open cluster formation? I'm puzzled by the 25 LY span. It seems quite a distance over which such a huge coordinated cataclysm could occur. 200 million years would seem a relative blink of the cosmic eye. Could cluster formation occur within a smaller region and then the resulting stars move apart 25 LYs within 200 MYs?

The stars in open clusters formed at the same time, in the same star-forming region. Such regions typically span tens of light years. Gas and dust not incorporated into stars is rapidly blown away by hot new stars, which leaves behind the young stars, many of which are gravitationally bound to each other- although weakly. That's what an open cluster is. Because the gravitational binding is weak, perturbations between the member stars as well as from surrounding stars or gas can easily break these formations up, which is why they have such short lifetimes- a few tens to a few hundred million years.

[Anthony Barreiro]

This is a beautiful image! Thanks Dieter.

This past weekend I was leading a skywatching weekend at Wilbur Hot Springs in Colusa County, northern California, where we were blessed with a clear dark sky. M7 was popular. Folks enjoyed comparing how this cluster and the milky way background look to the naked eye, through binoculars, and through an 8-inch telescope at 50x magnification. The fact that these stars are "only" a couple of hundred million years old raised a few eyebrows, and led to an interesting discussion of the life cycles of stars. So it's a pleasant memento to see this lovely picture.

[Doc in SF]

This is a beautiful image! Thanks Dieter.

This past weekend I was leading a skywatching weekend at Wilbur Hot Springs in Colusa County, northern California, where we were blessed with a clear dark sky. M7 was popular. Folks enjoyed comparing how this cluster and the milky way background look to the naked eye, through binoculars, and through an 8-inch telescope at 50x magnification. The fact that these stars are "only" a couple of hundred million years old raised a few eyebrows, and led to an interesting discussion of the life cycles of stars. So it's a pleasant memento to see this lovely picture.

Yes, the image was beautiful. Your account of people pondering what 250 million years meant to a star got me to think about what was happening on earth 250 mya! Well, Earth had a single continent straddling the equator and was recuperating from the largest mass extinction of species in our history. Perhaps a turtle or two looked up and saw an evolving star cluster but not many beings.

It made me wonder. If we can locate a few photos of protostar clusters that would appear today similar to what that turtle looked at 250mya. Perhaps a section of the Pillars of Creation would be a good candidate. Any others?

[raindrop]

Someone please tell me how Ptolemy could have seen it without a telescope?

[Chris Peterson]

Someone please tell me how Ptolemy could have seen it without a telescope?

The same way anybody can... with his eyes. It's an easy naked eye object from any relatively dark site south of the middle northern latitudes. Note that Ptolemy considered it a nebula, which is how many small clusters appear to the naked eye- a telescope allows it to be resolved into individual stars.

[Anthony Barreiro]

Yes, the image was beautiful. Your account of people pondering what 250 million years meant to a star got me to think about what was happening on earth 250 mya! Well, Earth had a single continent straddling the equator and was recuperating from the largest mass extinction of species in our history. Perhaps a turtle or two looked up and saw an evolving star cluster but not many beings.

It made me wonder. If we can locate a few photos of protostar clusters that would appear today similar to what that turtle looked at 250mya. Perhaps a section of the Pillars of Creation would be a good candidate. Any others?

I would imagine that when they were born these stars were still deeply shrouded in their natal cloud of gas and dust. Maybe the whole thing was an emission / reflection nebula like the Trifid.