Coathook to the stars

By Phil Plait | July 26, 2012 6:43 am

In the constellation of Vulpecula, the fox – located high in the sky this time of year for northern hemisphere observers – is a fun little asterism: a collection of stars formally known as Brocchi’s Cluster, or Collinder 399. Greek astrophotographer Anthony Ayiomamitis took a grand picture of it just a few days ago that I have to share with you:

[Click to enhaberdasherate.]

It’s very pretty, isn’t it? The asterism itself is composed of the ten or so brightest stars you see; the rest are background stars. It’s most likely not a true cluster; that is, the stars may be at different distances and not physically associated with one another.

Still, this so happens to be one of my all-time favorite objects in the sky. Why? Because of the shape of the cluster: it really looks like a coathanger! If you don’t see it, I drew lines between the stars in question in the image inset here.

Now you see it, right? Astronomy Picture of the Day featured a different shot of the Coathanger in 2008, too, which is worth a look.

This group of stars is pretty big – three times the width of the full Moon on the sky – and bright, making it really easy to spot with binoculars. In fact, when I was younger I stumbled on it myself by accident while scanning that part of the sky with my telescope. It was obviously shaped like a coathanger, and I was delighted to find out that’s what everyone called it.

In fact, now that I think about it, it’ll be very well placed for observing in September, making it a great target for folks coming to Science Getaways. That would be fun. But if you have clear skies this time of year, it’s easy to find, about a third of the way from the bright star Altair to Vega, in the Summer Triangle. Give it a shot!

Image credit: Anthony Ayiomamitis, used with permission.


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Comments (21)

  1. John Kennell

    I saw this one (I think) through binoculars when I was a kid. If you turn the picture upside down, it resembles a front elevation view of the Enterprise, 1701.

  2. Timmy

    That’s no hanger, that is Gandalf the Grey’s hat!

  3. Matt

    Why does the “hook” face different directions in the picture from Anthony and the one taken in 2008?

  4. What is the difference between an asterism and a constellation?

  5. Larry

    My god, its full of stars!

    #4 Carl: Asterisms are recognizable patterns of stars. Constellations are defined areas of the sky which contains asterisms. Their names come from asterisms defined by someone who thought some of the stars looked like something, e.g., Ursa Majoris, the big bear.

  6. VinceRN

    When I bought my first real telescope (8″ Newtonian) this was the first deep sky object I looked at. It was kind of upsidedownish so it took me a while to make a coat hanger out of it though.

  7. I see a man wielding a scythe.

    But then I’m weird.

  8. AliCali

    @3 Matt

    “Why does the ‘hook’ face different directions in the picture from Anthony and the one taken in 2008?”

    Images in telescopes get flipped differently, depending upon the type of telescope. Some rotate the image 180 degrees, while others do a mirror image.

    If you want to compare two photos from different telescopes, you often have to rotate, crop, and sometimes mirror image one of the photos to make the orientation match.

  9. Kirsti

    +1 Gandalf’s hat

  10. Rob G

    My favorite is the Owl Cluster (NGC 457). Much more dramatic than a plain old coat hanger, if you ask me.

  11. Aaron

    I stumbled across this one myself at a star party just this past Saturday! As most of my time is spent under gloomy city skies and none of my star charts seem to label this asterism, I was completely taken by surprise when it appeared within my telescope’s field of view. In excitement, I announced loudly, “hey, there’s a coat hanger near Altair!,” to which a more experience astronomer replied, “yep, there’s a coat hanger up there!”

  12. Kim

    I think it looks like a big tidal wave. Where is the surfer?

  13. Wildride

    “No, I wasn’t doing that with a coathanger. I just locked my keys in there.”

  14. Curt

    Phil said that these stars are “most likely not a true cluster; that is, the stars may be at different distances and not physically associated with one another.”

    Why is it that we don’t know for certain? Am I mistaken? … (likely so)… But I thought we could determine movement and distance of stars. Someone please enlighten me.

    Thanks!

  15. Bill Gresho

    Do enjoy your site. You are NOT a bad astronomer! Admittedly occasional corny humor, but but still a very informative site. Thank you.

    From a former kid astronomy buff — like 55 years ago. Walked the barrel, grinding and polishing, “constructing” a six inch Newtonian.

    Now for the question. What is “high in the sky”? On the horizon toward the North or up at the zenith? Sorry. Serious question from a senile 70 year old.

  16. This Coathanger asterism is also known as Brocchi’s Cluster or / and Collinder 399 among other things and has been discovered independently quite a few times by different people as it’s wikipedia page (linked to my name here) notes.

    @14. Curt – From that wikipedia entry :

    The group was considered to be a cluster for most of the 20th century. Looking at a variety of criteria, however, a study in 1970 concluded that only 6 of the brightest stars formed an actual cluster. Several independent studies since 1998 have now determined that this object is not a true cluster at all, but rather just a chance alignment of stars. These recent studies have generally based their findings on improved measurements of parallax and proper motion provided by the Hipparcos satellite which were first published in 1997.

    The BA might perhaps have been using an older source thus explaining that uncertainty.

    Jim Kaler’s excellent ‘Stars’ website also has a great entry on this asterism noting that three of its stars have Flamsteed numbers – specifically 7, 5 & 4 Vulpeculae.

  17. ^ See :

    http://stars.astro.illinois.edu/sow/cthng-t.html

    &

    http://stars.astro.illinois.edu/sow/vul-t.html

    Which give the Kaler’s ‘Stars’ links to the Coathanger asterism and Vulpecula constellation more broadly including photographic findercharts.

    Wikipedia page for 4 Vulpeculae is here :

    http://en.wikipedia.org/wiki/4_Vulpeculae

    Noting it is an orange giant star about 235 ly distant whilst 7 Vul is a B5 blue dwarf star located 760 ly away and 3 Vul is a B6 type blue giant star located 400 light years away as noted on their respective wiki-entries and the wiki- list of stars in Vulpecula which is linked to my name here.

    I presume the other un-Flamsteed numbered stars of the Coathanger / Brocchi’s Cluster / Collinder 399 would have other star catalogue designations – SAO / HD / HIP (etc ..) numbers but not sure what they are or their types and distances.

  18. PS. Almost forgot 5 Vulpeculae – the last of those Flamsteed lettered Coathanger stars is a Sirian type A0 V star located 218 light years away.

    Clearly these stars are at very different distances and as Brian A. Skiff of Lowell Observatory noted :

    By comparing pairs of stars on the list [Hipparcos catalogue – ed.], you can see that there is no pair with similar parallaxes and motions, much less a full cluster. For instance, stars 3 & 8 [HD 182620 an A2 V Sirian & HD 182972 an A1 V Sirian – ed.] have very similar parallax distances, and the uncertainties overlap considerably. However, comparison of the proper motions shows them to be moving in very nearly opposite directions on the sky. Thus though they could be near each other, their motions through space are different.”

    Source : Page 67, “Brocchi’s Cluster Revealed” article by B.A. Skiff in ‘Sky & Telescope’ magazine, January 1998.

    Info from the table incl. there added too btw. Good article by on the non-cluster-ness of Brocchi’s Cluster / Collinder 399 / the Coathanger if folks can find a copy somewhere.

    BTW. Red giant Anser (or shall we call it the goose star!) the lucida or brightest star in the constellation seems to be a member of the Arcturus stream, a group of stars with high proper motion and metal-poor properties thought to be the remnants of a small galaxy consumed by the Milky Way – Arcturus of course being the brightest example of that group in our skies! (Wiki-link to source in my name here.)

  19. Jon Hanford

    @14 Curt:

    In addition to the material noted by MTU above, here’s a link to a 1998 study, again using Hipparchos data, that found Collinder 399 to be a chance alignment of stars and not a bound cluster: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26A…340..402B&db_key=AST

  20. Curt

    @ Messier Tidy Upper…

    Just now came back to check for responses. A belated, but hearty “thank you” is certainly in order.

    I’m overwhelmed at how much has gone into studying these stars, and how difficult it’s been to accurately measure their movements and distances. I really thought it was a “simple” matter of parallax observation and red-shift determination. I should have known better. And now I do.

    Again… thank you.

  21. @ ^ Curt : No worries. Cheers! :-)

    @19. Jon Hanford : Thanks for that. :-)

    @15. Bill Gresho :

    Now for the question. What is “high in the sky”? On the horizon toward the North or up at the zenith? Sorry. Serious question from a senile 70 year old.

    Not *that* senile I think! Depends where you live (latitude esp.) and what time of night it is but usually I think “high in the sky” refers to being closer to zenith rather than more northerly. Sometimes o’ course its both!

    (Sorry, meant to answer that last night and forgot. No need to apologise for asking questions – some of us here actually love answering them! ;-) [Raises hand.] )

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