Herschel opens its eye!

By Phil Plait | June 19, 2009 9:44 am

Herschel, the largest far-infrared telescope ever launched into space, has taken its first image!

Herschel spies M51


That’s M51, better known as the Whirlpool Galaxy, a nearby spiral galaxy (well, 25 million light years is close on an intergalactic scale). It’s face-on to us, allowing us to see its magnificent spiral arms and all the structure therein. Herschel is sensitive to far-infrared light, much lower energy than what our eyes can see. In galaxies, the brightest emitter of that kind of light is dust located near and in between stars, and dust is created by stars when they are born (and when massive ones die). Star birth happens in the spiral arms of these kinds of galaxies, so when Herschel looked at M51 that’s what it saw: the spiral arms outlined by the warm dust within them. The brights spots are where dust is being warmed by young, massive stars. It’s falsely colored blue in the image, meaning it’s the highest energy flavor of IR light Herschel sees; to our eyes it would still be invisibly far in the infrared.

Herschel’s mirror

If you’re used to Hubble images, this one looks a little fuzzy. That’s because the resolution of a telescope — that is, how well it can resolve small objects — depends on the size of the mirror and the wavelength of light it sees. Optical light, the kind we see, has a far, far smaller wavelength than infrared, so images in optical light have much higher resolution, and look sharper.

But for science, we want to know how much better Herschel does than previous far-infrared telescopes, and that depends on its mirror. Herschel wins here by a lot: its mirror is 3.5 meters across! Spitzer, the NASA observatory that has been taking such wonderful IR images of celestial objects, has a mirror less than a meter across, so Herschel’s eye is far sharper. Compare!

Herschel and Spitzer compared

You can see that Herschel’s view of M51 is a lot sharper than Spitzer’s at these long wavelengths. This means that with Herschel, astronomers will have a better infrared view of the sky than ever before. [Update: To be clear, Spitzer was not optimized for wavelengths this far in the IR, so its resolution in that image above is actually not as good as what it could do at shorter IR regions; for example check out this stunning M51 image taken by Spitzer in the nearer infrared to see what it can do!]

And this is just the first image, a test of the telescope’s abilities. In the coming weeks, months, and years, we’ll be seeing far more from this new eye in the sky, and I am very much looking forward to seeing what it sees.

Tip o’ the dew cap to Amanda. Image credits: ESA and the PACS consortium (Herschel images), and NASA/JPL-Caltech / SINGS (Spitzer image)

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (44)

  1. David Akers

    Thanks for the comparison. I was surprised at first by the resolution because I’ve been inundated with images from Hubble, and totally forgot about the wavelength issues involved.

  2. Any likely surprises to come with clearer IR imagery?


  3. MarkW

    SnakeLinkSonic: If we knew that, they wouldn’t be surprises 😉

  4. rosebud

    So why is there a much brighter area at the tip of one arm than the other? I assume that’s a nursery area–or is it something behind this galaxy?

  5. Stone Age Scientist

    I thought Hershey’s makes chocolates. I didn’t know they launched a telescope into space…

  6. Flying sardines

    Heyyy! GO Herschel! Awesome! 8)

  7. Wow, I didn’t even recognize M51! The bridge over to NGC5195 is so solid and the core of 5195 so small it looks like an ordinary spiral, not an interacting one.

    My best view ever of a galaxy was of M51 up at Fan Mountain a few years ago after the spring open house was over. The 31″ Tinsley had a 50mm eyepiece in it and M51 was near the zenith. It looked like a freaking photograph, with the knots of star forming regions in the spiral arms clearly visible. Stunning!

  8. Grammar Nazi

    Like the use of the singular! ‘eye’ 😉

    Good accuracy!

  9. OFF TOPIC: The Florida Science stick figure contest has selected their top ten. According to scuttlebutt, my wife’s entry beat my entry… How humiliating!


  10. gopher65

    Richard Drumm: Whoa, you’re right. I didn’t even notice that. That’s pretty crazy. You can barely see the bridge in optical, while in infrared I didn’t even notice that I was looking at a second galactic core. Cool.

  11. Helioprogenus

    So what does that mean for the James Webb Space Telescope when it goes up? Since it functions in near-infrared (I believe), does the resolution of distant objects become fuzzier than that of the Hubble? I know the eventual size of the collecting area of the segmented mirrors will be about 6.5 meters (6 times greater than Hubble’s), so perhaps at this will help increase resolution. Still wouldn’t a telescope with a mirror area equal to this but operable in visible light produce pictures with unbelievable resolution? Couldn’t they allow for some visible light processing?

  12. Chris A.


    That bright spot is M51’s companion galaxy, AKA NGC 5195, a smaller galaxy which interacted with M51 some time ago, and is currently slightly farther from us than M51. Evidence of the interaction can be seen as a kink in M51’s spiral arm closest to NGC 5195.

  13. That’s a SCIENCE WIN! Neat image! :)

  14. Mchl

    So JWST will also use IR right? It’s supposed to have more than twice (diameter) as large mirror as Herschel. So we can expect almost similar gain in resolution between JWST and Hershel as between Herschel and Spitzer… I suppose… :) What a shame there are no plans for visible spectrum large space telescopes anytime soon…

    Still it will be great to see Spitzer vs Herschel vs JWST comparision of M51 😀 (not to mention all the other things we will see through them)

  15. Charlie Young

    Been a long time since optical physics for me. What is the relationship between increased mirror surface and increase in resolution? Is it a squared or other exponential increase?

  16. DrFlimmer

    @ Helioprgenus

    Our ground-based telescope are, thanks to adaptive optics, at least as good as Hubble by now. And they will become even better. So there is no need anymore for optical telescopes in space.
    However, the atmosphere blocks most other parts of light. And especially IR is critical to look into dust-obscured regions like the galactic center and star-forming molecular clouds. So, a big IR telescope in space is worth the effort! And since Herschel is FIR and JWST is supposed to be NIR they do not really compete with each other (AFAIK).

  17. Dribble. And indeed, drool. Not a bad happy-snap for 25 million Lights away…..!

  18. IVAN3MAN

    Phil Plait:

    Herschel wins here by a lot: it’s mirror is 3.5 meters across! Spitzer, the NASA observatory that has been taking such wonderful IR images of celestial objects, has a mirror less than a meter across, so Herschel’s eye is far sharper. Compare!

    My eyes are sharper than yours, Phil; that should be: its mirror


  19. What is dust, anyway? Is it dirty junk like iron and carbon and more complex compunds? I have ruled out lint. Is it molecular like gas (either single atoms, or a few bound atoms forming a gas) or is it larger bits like sand, pebbles, rocks, etc.?

  20. Thanks Flimmer, thats more or less what I was looking for.


  21. Jason Nyberg

    “Evidence of the interaction can be seen as a kink in M51’s spiral arm closest to NGC 5195.”

    :) In my eyes the evidence is the pair of highly defined spiral arms. This is the inevitable result of recent galactic “near misses”: Tidal forces subtly (or not so subtly) axially elongate the shape of the galaxy, and the differential in orbital speed between the outer fringe and inner core twists the elongation into a spiral, like poking a stick into to a towel and twisting.

    Mark my words, anytime you see a well-defined double-armed galaxy, you’ll find its partner nearby…

  22. Mchl

    @PsyberDave: I suppose it’s hydrogen mostly

  23. @ PsyberDave:

    Select my username for a link to an Astronomy Picture of the Day posting from 2003 July 6 which answers this question quite well.

    To quote from the article:
    Our universe is a very dusty place. Dust usually shows its presence by blocking out light emitted from stars or nebulae behind it, sometimes creating the illusion of a horse’s head or a sombrero hat. But nobody really knows what a typical interstellar dust grain looks like. By studying how dust absorbs, emits, and reflects light, astronomers do know that interstellar dust is much different than the cell and lint based dust found around a typical house. Interstellar dust grains are composed mostly of carbon, silicon, and oxygen and are usually less than about 1/1000 of a millimeter across. Recent work indicates that most dust grains are not spherical. The above picture shows the result of a fractal adhesion model for dust grains involving random conglomerates of spherical compounds of different properties, here artificially highlighted by different colors.

  24. Patrik Holmström

    @ Charlie Young

    The concept you want to look up is “Diffraction Limit”. Roughly the resolution is limited by wavelength/diameter of the optical system (+some constants etc). The problem with far infrared is that the wavelengths are *much* longer than visible light, in the case of the three cameras onboard Hershel 1000-10000 times longer!

  25. Chris A.

    @Charlie Young:
    Resolving power scales linearly with aperture: Double the diameter of your mirror and see details twice as small.

  26. FC

    Speaking of M51 It’s been used as background for a boardgame (the hubble image obviously!) take a gander here:


    Someday we’ll have very high IR resolution images just as good as hubble’s optical light images. Without the IR scopes we would never be able to see into the Galactic Center and other regions obscured by dust. Still there must be limitations, I don’t think the IR scope can look all the way across and show us what’s behind the core we see…

  27. Gary Ansorge

    Umm,Yummy,,,reminds me of a fractal I once saw.

    2. SnakeLinkSonic

    “Any likely surprises,,,”

    Ummm, no, I expect they will be UNlikely, ’cause if they were likely, they wouldn’t really be surprises,,,

    GAry 7

  28. Torbjörn Larsson, OM

    I thought Hershey’s makes chocolates.

    No, I’m pretty sure that is a Herschel bar galaxy: “M51 also has a small central bar (Pierce 1986; Zaritsky & Lo 1986).”

  29. Nice to have the Spitzer image next to Herschel’s for the comparison. All I can say is WOW!

  30. Wow that’s simply incredible. I can barely even fathom taking pictures from 25 million lightyears. I thought my 10x zoom was good!

    I am so excited for the day that we create lightspeed or nearlightspeed technology. Imagine how exciting it would to visit these galaxies that we can only take low resolution pictures of now.

  31. I spy with my 3.5 meter eye…..

    [yes, I have Finding Nemo on the table next to me]


  32. IVAN3MAN

    Err… Phil, have we overlooked something? 😉

  33. John Phillips, FCD

    Saw this on my Beeb science page RSS feed and was wondering when you would cover it. So cool, Science FTW and it’s only going to get better.

  34. Ivan

    Sadly, I have just read that one of the founders of Infrared Astronomy, Dr Frank J. Low. has died in Tucson, AZ, June 11, as reported by the New York Times, yesterday, June 20.

    His legacy is the proposed James Webb Space Telescope, being built to his design, and due to be launched in 2014.

    Phil, do you have any more details, or any connection in your career with the Pioneer of this particular facet of Astronomy?


  35. So, I cannot wait for this new Herschel craft to take images of the region around the galactic center. That mesmerizing region would be interesting to see in FIR.

  36. RightPaddock

    A major downside to getting older is that I wont get to see the telescopes of the future, I’ve no doubt they’ll be awesome

    Maybe we should be giving them nicks – this one could be Cyclops?

    It’s a long way from home so I guess there wont be any repair missions. It’s website says its got an operational life of 3 years – that’s not long, bit sad actually

    Well done ESA

  37. Astra

    “Our ground-based telescope are, thanks to adaptive optics, at least as good as Hubble by now. And they will become even better. So there is no need anymore for optical telescopes in space.”

    Not quite. Ground-based telescopes are competitive with HST over very small fields of view and while they will get better, they will not be able to engage in wide field imaging or diffraction-limited imaging at the short end of the optical passband (not to mention the UV) that could compete with a second-generation Hubble. We need both.

  38. mAck

    Its so amazing when you put the two shots here one in front of the other, all the dark zones correspond perfectly to the infrarred light zones, just like you made something out of nothing.

    GIF: http://www.freeimagehosting.net/uploads/3fd517267e.gif
    SWF (smoother, smaller size and colorful): http://megaswf.com/view/511c0d0d3f4ccf1238023d52ec38cef3.html

  39. DrFlimmer

    @ Astra:

    Yeah. But interferometry is also a tool that expands the power of ground-based telescopes. The ESO has tested it for their optical telescopes and it worked! Of course, building an interferometer with ground-based and space telescopes would really expand our view. So, yes, both are needed, but the urge is not so big…

  40. miguel

    i just had the weirdest trip. If the spiral galaxy is 25 million LIGHT years away, then is the picture a refraction of light from Whirlpool that originated millions of years ago? I.e., flip of the coin, if there was a telescope on Whirlpool Galaxy that took a picture of our galaxy, and imagine it could zoom in even further into this planet, then would it be looking at our planet but millions of years ago? If it could zoom in even further, could it see the dinosaurs?


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