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Ground-based Telescope as Sharp as Hubble

Posted by michael on from the corrective-lenses-required dept.

Midnight Thunder writes: "The BBC has an article describing how the Paranal Observatory has been able to take images that are just as sharp as the Hubble Space Telescope. For a ground based telescope the images are of amazing quality."

4 of 36 comments (clear)

  1. Corrective lenses? by Liquor · · Score: 3, Insightful

    It's interesting to note that the Paranal telescope modifies the mirror to correct for an imperfect lens (the atmosphere), while the Hubble has a corrective lens (installed in orbit) in it's system to correct for a manufacturing error in the mirror.

    It makes me wonder if the Hubble would have been significantly better than Paranal if the mirror had been made correctly in the first place.

    --

    Liquor
    Sanity is a highly overrated commodity.
    1. Re:Corrective lenses? by LMCBoy · · Score: 3, Insightful

      It's not a good analogy, because the correction used by Paranal is an adaptive optics system that continually updates the shape of the mirror 500 times per second to correct for the turbulent atmosphere, which causes images to bounce around in the focal plane (a/k/a the "twinkling" of stars). OTOH, the HST correction is static aberration correction, and therefore much simpler, technologically. HST doesn't need adaptive optics, because there is no atmosphere between it and its targets (that was the whole point of putting it in orbit).

      Furthermore, even if the HST mirror had been manufactured perfectly, it would be no better than the post-corrected HST. In other words, the HST fix made it "as good as new".

      Theoretically, once you have perfect optics, and have corrected for the atmosphere perfectly (if you're on the ground), the sharpest image you can achieve is limited by quantum mechanics; it's known as the diffraction limit. The size of a diffraction-limited point source is inversely proportional to the diameter of the aperture (i.e., the primary mirror).

      Since Paranal is a much larger telescope than HST, (8.2 meteres compared to 0.9), it's ideal, diffraction-limited image is much sharper than HST's. The fact that they can "only" get as good as HST shows you how hard adaptive optics is.

      --
      Liberal (adj.): Free from bigotry; open to progress; tolerant of others.
  2. CCD's and Image processing have come along way! by pease1 · · Score: 3, Interesting
    Image processing and cheap CCD detectors have REEEEALLLLYYY improved astro-imaging from the ground. In fact, it's restarted a dead line of astronomy: studing images instead of spectra and other forms of data.

    Amateurs are doing amazing stuff. Here's an image of Saturn taken with an amateur 13-inch scope and a camcorder. It's compared side-to-side with a similar HST image. You will be surprised.

    Dozens of amateurs joined in a program to supply images to the 2001 International Marswatch program during this past Martian observing season. The pros use these images to decide when to spend their valuable HST time to look at Mars. Some of the images (and visual drawings) are incredible.

  3. This is not new by lanclos · · Score: 3, Informative

    Keck's been capable of "beating" Hubble for a good long while now. Adaptive Optics is wild and crazy stuff.

    Please don't believe that we'll be able to do away with space-based observing because of this innovation. Our atmosphere absorbs an awful lot of interesting wavelengths.