The Seven WISE Sisters

By Phil Plait | July 19, 2010 7:04 am

If you live in the northern hemisphere and go outside in the winter, hanging not too far from Orion’s left shoulder is a small, tight, configuration of stars. A lot of people mistake them for the Little Dipper — I get asked about it all the time — but really it’s the Pleiades (pronounced PLEE-uh-dees), an actual cluster of stars about 400 light years away. To the eye you can usually spot six of the stars (the seventh, seen in ancient times, may have faded a bit since then), and in binoculars you can see dozens.

But when NASA’s Wide Field Infrared Survey Explorer (WISE) looked at it in February, this is what it saw:

WISE_pleiades

Coooool. Literally! WISE looks in the infrared, and can see cool objects that are invisible to our eyes. The Pleiades stars are bound together in a cluster by their own gravity, and are currently plowing through a dense cloud of dust and gas in the galaxy. The material has been warmed up by the hot stars, and glows in the infrared. Deep images in visible light also show the material, but it looks blue as it reflects the optical light from the stars. In the WISE images, we’re seeing the matter actually glowing on its own, emitting infrared light.

pleiadesWhen I was younger it was thought that this material was the leftover stuff from which the stars formed. But it was later found that the stars are older than first thought; about 100 million years old. While still quite young — the Sun is 4.5 billion years old! — that’s long enough for the original cocoon of material that made up these stars’ nursery to have dispersed. So it’s a cosmic coincidence that we happen to see the cluster as it’s ramming through this material. On the other hand, the Milky Way galaxy is loaded with lots of junk floating out there, and the Pleiades are in an area of high traffic. It’s not too surprising we’d see something like this happening, and it’s nice that it’s going on close enough that we get a good view of it.

WISE doesn’t just get pointed wherever astronomers see something interesting: it’s an all-sky survey, spinning on its axis and taking snapshots continuously. These are stored, and astronomers on the ground can then put them together in a mosaic. This image is actually pretty big, covering 2×3° of the sky. That’s about the size of a postage stamp held at arm’s length, and is a fair bit bigger than the full Moon on the sky. This image was released to celebrate the fact that as of July 17, WISE has now scanned the entire sky, and its primary mission has been fulfilled. Yay!

Funny, too: I’ve observed the Pleiades a lot, and seen lots of pictures too, yet it’s difficult to identify the stars in the WISE image — I had to rotate the visible image to match the one from WISE, but even then it’s not entirely obvious how they line up. In the IR, stars are bright that might be dim in optical, and vice-versa! But I’d recognize the sheets and filaments of the disturbed dust anywhere. One of my favorite things in astronomy is seeing a familiar object in an unfamiliar way. It reminds me that there’s still plenty to learn about the Universe.

Image credits: NASA/JPL-Caltech/UCLA and NASA, ESA and AURA/Caltech


Related posts:

A WISE flower blooms in space
Two nearby galaxies peek out through the dust
WISE uncovers its first near-Earth asteroid!
First spectacular views of the sky from WISE


CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (28)

  1. Matt T

    If you live in the northern hemisphere and go outside in the winter, hanging not too far from Orion’s left shoulder is a small, tight, configuration of stars.
    If you live in Boulder and go outside anytime, hanging on the front of everyone’s Outback is a very similar configuration of stars 8-)

    Oh, yeah. And cool pic/science/etc, obviously…

  2. Matt T:

    hanging on the front of everyone’s Outback is a very similar configuration of stars

    It took me a few moments to realize that you weren’t referring to the chain of steakhouses, and to get the joke. :-)

    (Or, as we old-timer Unix geeks might say, “Fhoneh” vf gur Wncnarfr anzr gur gur Cyrvnqrf.)

  3. Minos

    @Ken B: I think you mean “bs gur”.

  4. Minos, you are, of course, correct.

    Furrfu.

    And it’s too late for me to edit the post and say “what typo?” :-)

  5. @ Ken and Minos:

    Oh, murgatroyd! That is about as geeky a geek dropping as I’ve ever seen!

    Bravo, sirs! Bravo!

  6. Mandelbrot5

    When I was a kid in Colorado I could see the dim 7th sister, however I was at 8500 feet with no light pollution.

  7. David C

    Pleiades (pronounced Subaru :)

    http://www.naoj.org

  8. Paul from VA

    How recent is the change in thought about the Pleiades and the gas being a coincidence? I remember hearing as recently as about 7-8 years ago that the gas was leftover from the formation…..

  9. dachs_dude

    Ken B.

    By “Outback”, I think Matt T is referring to the Logo on the front of Subaru automobiles. Subaru means seven sisters.

    There was a book a few years back on naked eye astronomy and there was a chapter featuring a Subaru.

  10. dachs_dude:

    By “Outback”, I think Matt T is referring to the Logo on the front of Subaru automobiles. Subaru means seven sisters.

    I guess you don’t grok rot13? :-)

    “Fhoneh” vf gur Wncnarfr anzr sbe gur Cyrvnqrf.

    (Typo corrected. Thanks, Minos.)

  11. mike burkhart

    This is grate .The Pleiades is my favrote star cluster . Thro my telescope I can see 10 or 20 stars (I never bothered to count) .

  12. NAW

    They are just hating us on our non-knowledge in Unix. And all I have is a couple of Foxtrot comics to help me at least know something is going on.

    That is an awesome image though.

  13. dachs_dude

    Ken;

    I don’t “grok rot13″.

    But then, again, I don’t grok “reality” TV either :)

    Roger

  14. magetoo

    rot13? There’s a bookmarklet for that. (here, just drag the button-like link to where you would like to have it) It can be useful for spoiler text, like just now.

    Not that I need help to read rot13 text, of course. *cough*

  15. Steve

    My Dad, who knew his stars, used to refer to the “Big Dipper”, the “Little Dipper”, and Pleiades as the “tiny winy dipper”

  16. Perry Doliah says the cloud looks just like an angry cephalopod.

  17. Holy smokes, those are lovely images.

    “…as of July 17, WISE has now scanned the entire sky…”? That’s fantastically fast. And to think it took James Joyce seventeen years to write “Finnegans Wake,” which is a universe in itself.

  18. Messier Tidy Upper

    Great image thanks WISE. :-)

    The Pleiades or “Subaru” to the Japanese is also Messier 45 as well as being called the “Seven Sisters”.

    Did y’all know that the Pleiades was originally counted as a separate constellation in its own right by the early greeks?

    Plus how many here can name all of the individual (well seven major) stars?

    I’ll give you a while to try then scroll down for the answer & a link to Kaler’s image of them all & Kaler’s info on a couple of them.

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    Okay, the Pleiads or “Seven Sisters” are :

    1) Alycone -the lucida or brightest member
    2) Merope – which has some nebulosity nearby
    3) Maia
    4) Taygeta
    5) Electra
    6) Caelano
    &
    7) Pleione – a shell star which may be the one that faded.

    Then there’s also the star named Atlas among the Pleiades as well apparently their mythological father if I’m remembering my Greek legends right. Which may or may not be the case – &, btw. greek legends also come in a number of different variants too. :-)

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

    & http://stars.astro.illinois.edu/sow/alcyone.html &
    http://stars.astro.illinois.edu/sow/merope.html

  19. on

    How can you tell they’re plowing into the gas versus the gas being moved over them? Or both?

  20. on

    How can you tell the collection of stars is plowing into the gas, versus the gas moving over them? Or both?

  21. Colin

    It’s not just the Northern Hemisphere that they can be seen. It’s currently Matariki (Maori New Year) http://en.wikipedia.org/wiki/Matariki

  22. on:

    How can you tell the collection of stars is plowing into the gas, versus the gas moving over them?

    Einstein says it doesn’t matter. :-)

    Though, perhaps, it might be that one is moving faster relative to the rest of the galaxy.

  23. Blaidd Drwg

    Is it just me, or does that picture look a bit like Van Gough’s “Starry Night”?

    Seems he saw a lot more than we give him credit for – where’s The Doctor when you need him???

  24. Jon Hanford

    “I’ve observed the Pleiades a lot, and seen lots of pictures too, yet it’s difficult to identify the stars in the WISE image……But I’d recognize the sheets and filaments of the disturbed dust anywhere. One of my favorite things in astronomy is seeing a familiar object in an unfamiliar way.”

    Same here, Phil. Images of the Pleiades at some wavelengths make identification much harder. This ROSAT X-ray view of M 45 shows only the hot stellar members (and none of the dust): http://antwrp.gsfc.nasa.gov/apod/ap990828.html

    [Luckily, green boxes mark the position of the seven brightest visual stars in this image :) ]

  25. magetoo

    Did y’all know that the Pleiades was originally counted as a separate constellation in its own right by the early greeks?

    You mean that they are not counted as such now? That was news to me. (Clearly, my Classical Greek bias is shining through here.)

    But I’m pretty sure I actually did see the Pleiades mentioned as a separate constellation as a kid, though. I guess I have to look things up…

  26. Sion

    We say PLY-ad-eez here in the UK.

  27. hermagix

    I live in a zone where it is normal to spy the Pléyades, nevertheless, the persons who do not have astronomic knowledge they are called them Seven Little Goats, and it is something graceful.
    Once I was lucky to see across a telescope the belt of orion, and though to simple sight one does not see almost anything with the telescope hundreds of stars were observed.
    Certainly, my language is Spanish and my English is not very good.

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