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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 image, taken last June from Hungary through a small telescope, combines over 60 two-minute exposures. 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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Ah yes, the M7 cluster. It is a fine young cluster seen against old yellow stars in the bulge of the Milky Way, as bewildering in number as the grains of sand on a beach.

That's a fine APOD!

Ann

"Also visible are ... literally millions of stars." Literally? This is a popular claim for astronomy pictures but is rarely true. The full size photo obtained by clicking on today's APOD (very nice, as usual) is composed of three million pixels. For there to be even one million stars visible there could be no more than 3 pixels/star. Sorry to be so pedantic. But I do believe that there would be millions of stars visible with much higher resolution.

What is the significance of the term “open” in open star cluster? Is there also a closed star cluster? Is there some reason to not just call them a star cluster? Just curious.

muehlner wrote:"Also visible are ... literally millions of stars." Literally? This is a popular claim for astronomy pictures but is rarely true. The full size photo obtained by clicking on today's APOD (very nice, as usual) is composed of three million pixels. For there to be even one million stars visible there could be no more than 3 pixels/star. Sorry to be so pedantic. But I do believe that there would be millions of stars visible with much higher resolution.

There is probably more than one star for many of the pixels becoming a dim haze in the darker areas. I suppose you could say you are literally seeing trillions of water molecules anytime you look at a photo of a cloud. It wouldn't be incorrect!

muehlner wrote:"Also visible are ... literally millions of stars." Literally? This is a popular claim for astronomy pictures but is rarely true. The full size photo obtained by clicking on today's APOD (very nice, as usual) is composed of three million pixels. For there to be even one million stars visible there could be no more than 3 pixels/star. Sorry to be so pedantic. But I do believe that there would be millions of stars visible with much higher resolution.

I'm happy enough with three million pixels -- I need to reduce it to view the whole image on my monitor. I'm quite prepared to accept that there are millions of stars in the FOV. My eyes are connected to my brain which can visualise the rest. (And maybe the author's original was reduced for publication on the web.)

Mactavish wrote:What is the significance of the term “open” in open star cluster? Is there also a closed star cluster? Is there some reason to not just call them a star cluster? Just curious.

AFAIK, open clusters are not as tightly bound as globular clusters, and both are star clusters.

Nitpicker wrote:AFAIK, open clusters are not as tightly bound as globular clusters, and both are star clusters.

If it looks nearly identical to a pile of salt dropped onto a piece of black velvet, it's a globular cluster.

Mactavish wrote:What is the significance of the term “open” in open star cluster? Is there also a closed star cluster? Is there some reason to not just call them a star cluster? Just curious.

Nitpicker wrote:AFAIK, open clusters are not as tightly bound as globular clusters, and both are star clusters.

Right, the stars in open clusters will all eventually disperse, while globulars seldom lose members.

geckzilla wrote:

Nitpicker wrote:AFAIK, open clusters are not as tightly bound as globular clusters, and both are star clusters.

If it looks nearly identical to a pile of salt dropped onto a piece of black velvet, it's a globular cluster.

Whoa there, too technical geckzilla!

This is an amazing image of a very rarely imaged star cluster, the stars are like glittering sapphires on the golden galactic beach! There's so many cool open clusters in Scorpius, they will have their day (night?) to shine in the future!

BDanielMayfield wrote:Right, the stars in open clusters will all eventually disperse, while globulars seldom lose members.

Actually old globular clusters lose many stars as they orbit around the galaxy until eventually they are completely absorbed into the galactic disc. Many old globular clusters are now known to possess tidal tails, which is the result of ejected stars being drwan out in a stream as the globular cluster moves forward.

starsurfer wrote:

BDanielMayfield wrote:Right, the stars in open clusters will all eventually disperse, while globulars seldom lose members.

Actually old globular clusters lose many stars as they orbit around the galaxy until eventually they are completely absorbed into the galactic disc. Many old globular clusters are now known to possess tidal tails, which is the result of ejected stars being drwan out in a stream as the globular cluster moves forward.

I'm glad to have my understanding refined, so thanks starsurfer. But, with their orbital planes being often at large angles to the galactic disc's plane, wouldn't stars stripped from globulars mostly become members of the halo population instead of the disc?

BDanielMayfield wrote:

starsurfer wrote:

BDanielMayfield wrote:Right, the stars in open clusters will all eventually disperse, while globulars seldom lose members.

Actually old globular clusters lose many stars as they orbit around the galaxy until eventually they are completely absorbed into the galactic disc. Many old globular clusters are now known to possess tidal tails, which is the result of ejected stars being drwan out in a stream as the globular cluster moves forward.

I'm glad to have my understanding refined, so thanks starsurfer. But, with their orbital planes being often at large angles to the galactic disc's plane, wouldn't stars stripped from globulars mostly become members of the halo population instead of the disc?

They would.

Anyway, globular clusters are remnants of events that happened in the young, gas-rich, metal-poor universe. There are a few populous blue clusters today, for example R136 in the Large Magellanic Cloud, but they are not considered globular clusters since they are so "chemically different" from the old globular clusters. Moreover, R136 likely doesn't contain as many stars as the "typical present-day Milky Way globular cluster" did when it was young.

Ann

The dark nebula cloud.....THE JOKER.....flamboyantly lighting up a cigar.....

And on the other side....a Butterfly!!!

Really nice detailed picture. And just look at that "Wall of Stars"....


:---[===] *

Boomer12k wrote:And just look at that "Wall of Stars"....

That's the Hollywood Milky Way "Wall of Fame".

Here's a pleasant coincidence!

Stars in the Macrocosm and the Microcosm. See today's EPOD: http://epod.usra.edu/

John

The picture wasn't taken from Hungary, but from Africa, Namibia, Khomas-Highland.
The photographer is a Hungarian, his name is Lóránd Fényes .

muehlner wrote:"Also visible are ... literally millions of stars." Literally? This is a popular claim for astronomy pictures but is rarely true. The full size photo obtained by clicking on today's APOD (very nice, as usual) is composed of three million pixels. For there to be even one million stars visible there could be no more than 3 pixels/star. Sorry to be so pedantic. But I do believe that there would be millions of stars visible with much higher resolution.

Oh yeah, you just have to click on it for a higher resolution....then you'll find that there are literally millions of stars in the photo.

Javi Del Rey wrote:Oh yeah, you just have to click on it for a higher resolution....then you'll find that there are literally millions of stars in the photo.

The full resolution image has about three million pixels. Given the FWHM of about 2.5 pixels, and the fact that most stars occupy five or more pixels, there are probably no more than a few hundred thousand individually resolved stars in the image. So the caption is technically incorrect, even though it's clearly true that there are millions of stars in this particular field of view, and the image itself shows the light of millions.

BDanielMayfield wrote:

starsurfer wrote:

BDanielMayfield wrote:Right, the stars in open clusters will all eventually disperse, while globulars seldom lose members.

Actually old globular clusters lose many stars as they orbit around the galaxy until eventually they are completely absorbed into the galactic disc. Many old globular clusters are now known to possess tidal tails, which is the result of ejected stars being drwan out in a stream as the globular cluster moves forward.

I'm glad to have my understanding refined, so thanks starsurfer. But, with their orbital planes being often at large angles to the galactic disc's plane, wouldn't stars stripped from globulars mostly become members of the halo population instead of the disc?

Yes you're right, it would be the halo. I should have been more clear, I was just referring to the overall galaxy.

JohnD wrote:Here's a pleasant coincidence!

Stars in the Macrocosm and the Microcosm. See today's EPOD: http://epod.usra.edu/

John

That's a lovely picture.

(And as a color commentator, I note that those Earthly beads are star-colored, too.)

Ann

I was comparing M7 to M45 (The Pleiades Star Cluster) similar appearance.

http://apod.nasa.gov/apod/ap120903.html

Short-timers on the cosmic scale, it’s odd that they won’t be around for long either. Talk about fast and furious. Being from similar origins, the large number of open clusters must represent an interesting chapter in our galaxy’s history. Charles Messier must have been curious too. It seems like cheating we have so much information at our finger tips when he struggled night after night to complete a catalogue. Wonder if he knew the impact his work would have on the following generations during his lifetime?

Guess I could Google it.

Ron-Astro Pharmacist wrote:Short-timers on the cosmic scale, it’s odd that they won’t be around for long either. Talk about fast and furious. Being from similar origins, the large number of open clusters must represent an interesting chapter in our galaxy’s history.

New open clusters are forming all the time. Best to think of them as a process rather than historical events.

Chris Peterson wrote:The full resolution image has about three million pixels. Given the FWHM of about 2.5 pixels, and the fact that most stars occupy five or more pixels, there are probably no more than a few hundred thousand individually resolved stars in the image. So the caption is technically incorrect, even though it's clearly true that there are millions of stars in this particular field of view, and the image itself shows the light of millions.

None of the stars are resolved. Apart from the Sun, we never really sees stars, but unresolved point sources of light. Whilst it would always be technically more correct to say that "visible is the light from literally millions of stars", I think that it is fair enough plain English to say that "visible are literally millions of stars".

Nitpicker wrote:None of the stars are resolved. Apart from the Sun, we never really sees stars, but unresolved point sources of light. Whilst it would always be technically more correct to say that "visible is the light from literally millions of stars", I think that it is fair enough plain English to say that "visible are literally millions of stars".

When referring to optical point sources (such as most stars), the term "resolution" refers to the ability to distinguish two or more close sources from each other, not to the ability to resolve them as extended objects. So it is proper and correct with an image like this to say that tens or hundreds of thousands of stars are resolved.

Chris Peterson wrote:

Nitpicker wrote:None of the stars are resolved. Apart from the Sun, we never really sees stars, but unresolved point sources of light. Whilst it would always be technically more correct to say that "visible is the light from literally millions of stars", I think that it is fair enough plain English to say that "visible are literally millions of stars".

When referring to optical point sources (such as most stars), the term "resolution" refers to the ability to distinguish two or more close sources from each other, not to the ability to resolve them as extended objects. So it is proper and correct with an image like this to say that tens or hundreds of thousands of stars are resolved.

Damn, you're quite right about the different meanings of "resolved". Silly me, I knew that but my insomnia is making me dopey! I am still happy with " visible are literally millions of stars". I would also be content with the addition "many thousands of which are resolved".