APOD: Collinder 399: The Coat Hanger (2015 Aug 26)

[APOD Robot]

Collinder 399: The Coat Hanger

Explanation: Is this coat hanger a star cluster or an asterism? This cosmic hang-up has been debated over much of last century, as astronomers wondered whether this binocular-visible object is really a physically associated open cluster or a chance projection. Chance star projections are known as asterisms, an example of which is the popular Big Dipper. Recent precise measurements from different vantage points in the Earth's orbit around the Sun have uncovered discrepant angular shifts indicating that the Coat Hanger is better described as an asterism. Known more formally as Collinder 399, this bright stellar grouping is wider than the full moon and lies in the constellation of the Fox (Vulpecula).

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[Ann]

Ah! The CoathanRger is one of my favorite asterisms. It often shows up very well in astrophotos and helps you figure out what part of the sky the the picture is showing you!

Nice picture! RGB and all!

Ann

[Hans Vonk]

"... this bright stellar grouping is wider than the full moon..." The span of the picture is therefore about one degree. It would be nice if an indication of the span could come with every image.

[Joules]

So are the red far and the blue close, vice versa, or some mixture of the two?

[Ann]

So are the red far and the blue close, vice versa, or some mixture of the two?

I can't look it up right now, but I believe that the reddest one is a quite bright giant. I'm pretty sure that the reddest one is the brightest of the lot (say,~500 times solar), because the blue ones are relatively modest (say, ~100 times solar). The reddest star should be the most distant one.

Ann

[neufer]

So are the red far and the blue close, vice versa, or some mixture of the two?

• The far ones are blue, the nearer ones are a mixture of the two:

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Code: Select all

Dist. (LY)  Spectral type    Name     Apparent
 .                                    magnitude
-----------------------------------------------
237.7         A0V          5 Vul 	    5.594
271.6         K0III        4 Vul 	    5.16
387           K3IVp        HD 182293 	7.111
480           A0V          HD 182761 	6.303
613           M0III        HD 182955 	5.87
...............................................
805           A1V          HD 182972 	6.629
1160          B5Vn         7 Vul 	    6.327
1340          B3II         HD 183261 	6.875
1380          B9.5V        HD 182422 	6.398

[Chris Peterson]

Explanation: Is this coat hanger a star cluster or an asterism?...

Chance star projections are known as asterisms

The Coat Hanger - and any other notable stellar grouping- can be both a cluster and an asterism. "Asterism" does not demand a chance grouping of unrelated stars. The Pleiades, for example, is widely recognized both as an asterism and an open cluster.

The question here is whether the Coat Hanger is an open cluster or not, not whether it's an asterism.

[Chris Peterson]

So are the red far and the blue close, vice versa, or some mixture of the two?

Are you perhaps thinking of the redshift of more distant objects? If so, that only applies over cosmological distances (the distance between galaxy clusters and greater). There is no relationship between distance and redshift for shorter distances, and certainly not within our galaxy.

[neufer]

Explanation: Is this coat hanger a star cluster or an asterism?...

Chance star projections are known as asterisms

The Coat Hanger - and any other notable stellar grouping- can be both a cluster and an asterism. "Asterism" does not demand a chance grouping of unrelated stars. The Pleiades, for example, is widely recognized both as an asterism and an open cluster.

The question here is whether the Coat Hanger is an open cluster or not, not whether it's an asterism.

<<In the formal sense used here, asterisms are groups of stars that have not been categorized as something else. Objects which do not fall within the bounds of this definition include the Milky Way, nebulae, and open clusters. Open clusters are groups of stars that are physically related — gravitationally bound together and moving through the galaxy in the same direction and speed. As these groupings are not human constructs, but real phenomena, they do not count as asterisms. Among the best-known and closest are the Pleiades (M45) and the Hyades in Taurus and the Beehive (M44) in Cancer. (It may be noted that, with the addition of Aldebaran, which is in the same line of sight, the Hyades open cluster forms a V-shaped sectional asterism in Taurus).>>

[Steve Dutch]

Why is the Big Dipper only an asterism and not a constellation? Because Ursa Major includes many more stars than just the Dipper, as reference to a sky atlas with constellation boundaries will reveal. For the same reason, Pegasus is a constellation but the Great Square of Pegasus is an asterism. Cygnus is a constellation but the Northern Cross is an asterism. Sagittarius is a constellation but the Teapot is an asterism. A good example of an inter-constellation asterism is the large Y formed by Arcturus, epsilon and gamma Bootis and alpha Coronae Borealis.

[Chris Peterson]

<<In the formal sense used here, asterisms are groups of stars that have not been categorized as something else. Objects which do not fall within the bounds of this definition include the Milky Way, nebulae, and open clusters. Open clusters are groups of stars that are physically related — gravitationally bound together and moving through the galaxy in the same direction and speed. As these groupings are not human constructs, but real phenomena, they do not count as asterisms. Among the best-known and closest are the Pleiades (M45) and the Hyades in Taurus and the Beehive (M44) in Cancer. (It may be noted that, with the addition of Aldebaran, which is in the same line of sight, the Hyades open cluster forms a V-shaped sectional asterism in Taurus).>>

That's simply wrong. The Pleiades and Hyades are certainly considered asterisms.

[neufer]

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• the Coat Hanger
  Catheter Hogan

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[Beyond]

Click to play embedded YouTube video.

[Susie Q]

“Thank goodness for all the things you are not, thank goodness you're not something someone forgot, and left all alone in some punkerish place, like a rusty tin coat hanger hanging in space.”

Thanks to Dr Seuss for this quote....it came to mind this morning as I viewed the Coat Hanger in Space!

[starsurfer]

Ah! The CoathanRger is one of my favorite asterisms. It often shows up very well in astrophotos and helps you figure out what part of the sky the the picture is showing you!

Nice picture! RGB and all!

Ann

Thank god it doesn't have narrowband Ha and OIII exposures!!!

[neufer]

Click to play embedded YouTube video.

“Thank goodness for all the things you are not, thank goodness you're not something someone forgot, and left all alone in some punkerish place, like a rusty tin coat hanger hanging in space.”

Thanks to Dr Seuss for this quote....it came to mind this morning as I viewed the Coat Hanger in Space!

[starsurfer]

“Thank goodness for all the things you are not, thank goodness you're not something someone forgot, and left all alone in some punkerish place, like a rusty tin coat hanger hanging in space.”

Thanks to Dr Seuss for this quote....it came to mind this morning as I viewed the Coat Hanger in Space!

That's a very pertinent quote. You're not a dancer by any chance with a name like that?

[Joe Stieber]

"... this bright stellar grouping is wider than the full moon..." The span of the picture is therefore about one degree. It would be nice if an indication of the span could come with every image.

Actually, the long dimension of the "stick figure" seen on the overlay is very nearly 1.5 degrees (about three moon diameters) and the height of the hook is nearly 0.5 degrees, or about one moon diameter. The picture frame is about 2 degrees wide by 1.2 degrees high.

There's also a true open cluster, NGC 6802 (Collinder 400), off the east end of the hanger bar. It's just outside the frame, above-right of the "double star" near the right edge. It's a nice telescopic object visually, but one of those often-overlooked smaller/dimmer objects near a well-known object.

[Ron-Astro Pharmacist]

Looking at the photographer's site it appears this image may have been taken from Ohio. From the northern hemisphere doesn't it appear like this?

Not that it takes way from its natural aesthetics or that one hemispheres perspective is how it should be displayed but, to me, it might be more accurate to show it as it's seen from where it was taken. I remember seeing it the other night while watching the Perseids and, from my memory, it hangs very uncoathanger-like in the northern sky. I'm probably being supercilious though that's oxymoronic for me. Sort of like today's image – the same but different.

How about – Collinder 399 : The Cosmic Question Mark? Depending on where you stand. And that it's not wire!! Ever!!

Click to play embedded YouTube video.

[Joe Stieber]

Looking at the photographer's site it appears this image may have been taken from Ohio. From the northern hemisphere doesn't it appear like this?

Indeed, with a direct view (binoculars) from mid-northern latitudes, the Coat Hanger does look more-or-less upside-down, as shown in Ron's diagram, because the hanger bar runs largely east-west and the hook extends southward. As presented, today's APOD is rotated 180 degrees compared to Ron's diagram, which is the nominal view when the Coat Hanger transits the meridian. As it rises towards, or descends from the meridian, it is tilted somewhat, but still generally upside-down looking.

[JohnChumack]

Looking at the photographer's site it appears this image may have been taken from Ohio. From the northern hemisphere doesn't it appear like this?

Indeed, with a direct view (binoculars) from mid-northern latitudes, the Coat Hanger does look more-or-less upside-down, as shown in Ron's diagram, because the hanger bar runs largely east-west and the hook extends southward. As presented, today's APOD is rotated 180 degrees compared to Ron's diagram, which is the nominal view when the Coat Hanger transits the meridian. As it rises towards, or descends from the meridian, it is tilted somewhat, but still generally upside-down looking.

The reason it appears upside down compared to your binocular view is that telescopes invert, depends on the number of optical surfaces, binoculars do not invert the final image your eye perceives, so most images through telescopes will appear upside down or inverted image versus right side up view in Binoculars.
So this is how it appeared through my 5.5 " reflector telescope and camera viewfinder...also it depends on your orientation of your camera on the telescope as well. you may need to rotate the camera body to fit an object in your FOV as well.

[Ann]

Chris Peterson wrote:
That's simply wrong. The Pleiades and Hyades are certainly considered asterisms.

I thought asterisms are visual groupings of stars that just appear to belong together, but are at quite different distances from the Earth. Alternatively, asterisms might be several stars that are passing rather close to one another, but are moving in quite different directions at different velocities, and display different ages and metallicities. Above all, I thought that asterisms are apparent groups of stars that weren't born from the same natal cloud. By contrast, groups of stars where all the prominent members were born from the same natal could (or compact region of star formation) are called clusters.

Click to view full size image

The Hyades and the Pleiades.
Source: http://starryskies.com/The_sky/constell ... esian.html

All the prominent members of the Pleiades were born from the same natal cloud, so the Pleiades is a typical bona fide cluster. All but one of the prominent stars of the Hyades were also born from one and the same natal cloud, but the odd one out is the most prominent of the apparent members, brilliant orange Aldebaran. You might say that the Hyades is a true cluster, but the V-shape including Aldebaran is an asterism.

Click to view full size image

The Big Dipper. Source: http://www.skyandtelescope.com/astronom ... ds-a-star/

The Big Dipper is a good example of an asterism, because the two end stars, blue Alkaid and orange Dubhe, are unrelated to the rest. But the five middle stars - make that six if you count both Mizar and Alcor - may in fact have been born together, and could be regarded as a very loose cluster.

Ann

[Chris Peterson]

Chris Peterson wrote:
That's simply wrong. The Pleiades and Hyades are certainly considered asterisms.

I thought asterisms are visual groupings of stars that just appear to belong together, but are at quite different distances from the Earth.

Asterisms are patterns that people see in stars. Doesn't matter if the stars are independent (like the Big Dipper), or related (like the Pleiades). The "Seven Sisters" is the asterism that many people see in the Pleiades, although different cultures see that asterism differently (like most).

[DavidLeodis]

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[Chris Peterson]

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