Ground-based Telescope as Sharp as Hubble

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."

Comments

Corrective lenses?

[Liquor]

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.

Re:Corrective lenses?

[LMCBoy]

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.

Re:Corrective lenses?

[HorsePunchKid]

I did a lame research paper and classroom presentation on the Hubble Space Telescope way back in the day (read: I'm pretty sure of my info, but I'm not sure where to look for verification currently). Anyway, the result of my little grade-school investigations were that the in-orbit modifications they made improved HST significantly beyond its initial design. Actually, a little bit of looking turned up this: HST Servicing Missions. It's rather dumbed-down, but I think it'll help you draw comparisons.

In any case, there are a few things you should keep in mind. First, HST is quite old now, and past its initial proposed service lifetime, IIRC, so technology has come a long way since it went up. Second, things like this are often technologically lagging even before they go up, since it can take literally decades to plan an instrument of that size. Size is the other critical thing to keep in mind. It's (relatively) easy to build huge arrays like VLT on the ground, but try getting that into orbit :). Even if you break it up into many missions and assemble in-orbit (some early plans for NGST considered that, IIRC), it would still be a monumental task (though not impossible).

So I'd say in summary that chances are HST never could have been better than Paranal, even though it's been an awesome instrument throughout its lifetime.

Re:Corrective lenses?

[LMCBoy]

"The extra lense introduces a data loss. It will be removed in 2003"

Yeah, okay, no optic is perfect, but the loss caused by COSTAR is not significant.

Just FYI, while COSTAR won't be physically removed until 2003, it was permanently retracted out of the optical path a few weeks ago, in anticipation of the removal of the faint object spectrograph early next year (the last instrument that doesn't internally correct for Hubble's aberration).

cheers,
Jason

Huge News

[Fraser Cain]

This is enormous news when you consider the bottleneck of time the Hubble Space Telescope has become. If it works well, you can expect this technology to be applied to many ground-based observatories.

Then multiply it with the technology that merges the images from several mirrors to act like one giant mirror.

Finally, when you match this technology with the new technique devised to detect the atmospheres of distant planets, it really offers a lot to planet hunters.

I think this will revolutionize planet hunting, and bring the detection of Earth-sized planets with oxygen atmospheres within the near future.

Fraser Cain

Re:Huge News

[DerekLyons]

his is enormous news when you consider the bottleneck of time the Hubble Space Telescope has become. If it works well, you can expect this technology to be applied to many ground-based observatories.

They've tried many times to apply this and other technologies to ground based telescopes. The problem is that they've been very expensive and very high maintenance.

CCD's and Image processing have come along way!

[pease1]

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.

Re:CCD's and Image processing have come along way!

[jheinen]

What's really cool is that adaptive optics technology is already available for the amateur. Santa Barbara Instrument Group makes the AO-7 adaptive optics system that works with their ST-7 and ST-8 CCD imaging cameras. It retails for about $1200.

Not so sure...

[QuantumFTL]

IANAA, but I have a few comments neverthe less :)

First of all, visible light just isn't the best spectrum to do astronomy in for a lot of things, especially not the detection of extrasolar planets. Infrared radiation, unhindered by most space dust, and lower in energy, is clearly superior for studying things that are not giant balls of gas. The Next Generation Space Telescope and the Terrestrial Planet Finder both use infrared radiation to study objects of great interest that are difficult to study with something like the HST.

Interferometry, the technology you refer to that allows telescopes to combine their phase information to generate an image with angular resolution of that of a single larger telescope (through something known as apature synthesis) is only one of the many uses of intereferometry. Perhaps much more exciting than that is the ability of the Terrestrial Planet Finder to use nulling interferometry to selectively block out the radiation from a star, without blocking out the much fainter (millions of times less) glow of a circling planet.

Unfortunately the earth's atmosphere is mostly opaque to infra-red light, and room temperature objects (like most of the surface of the earth, and the telescopes on it) generate so much infra-red radiation that it makes it nearly impossible to do any far-infrared studies from the ground. The Darwin Project web site has a good explaination about the reasons terrestrial planet hunting should be done in space.

Ground based observatories will always have a place, however eventually it will be a matter of cost and convenience rather than any technical superiority.

Not saying this isn't cool, but it's mostly postponing the inevitable day when very little new astronomy can be done inside the confines of an atmosphere....

I think I saw something about this last night

[josepha48]

.. on a show about super black holes..

Aparently hubble which exists in space was so powerful at the time that it was put up there and it has the advantage that it does not have to go throuht the atmosperic distortion. However this new one is built on a mountain and is more powerful (newer technology) and is able to 'see' black holes at the center of galaxies. It seems that all galaxies have black holes, but not all black holes are feeding too. Of course the one at the center of our galaxy is feeding again... but don't worry, it wont eat us, at least not until after the andromedia galaxy collides with the milkyway in a few million years...

Re:I think I saw something about this last night

[Yazeran]

Yep, you are right (apart form the time-frame as others have pointed out), unless the Sun takes a near direct hit, the andromeda and our galaxy would pass each other without much fuss (at least in our part of it).

Granted, the shapes of the two galaxies would change dramatically, and perhaps the sun would be thrown out of the milkyway, but if that happened, the rest of the solar system vould follow, and the inner solar system would be largely unaffected.

The Oort cloud of snowballs (e.g. comets) would be affected though. So the inner solar system would experince some fancy fireworks in the sky when a lot of comets starts to appear. These comets may collide with earth (big 'BOOM' as on Jupiter a few years ago) but otherwise we (or who may be here at that time) would not notice.

Yours Yazeran

Plan: To go to Mars one day with a hammer.

Re:I think I saw something about this last night

[josepha48]

actualy according to the show, it depends on where the earth / sun is at the time of collision. If we are on one side we would feed the blackholes at the center and earth would die. If we are at the other side then we would get throw out as you describe.

Then again there is the change that earth would be somewhere in between and survive unharmed. I'd be suprised if the human race was still around then and evolution hadn't had another species tak our place.

This is not new

[lanclos]

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.

Re:This is not new

[apsmith]

One other advantage of space-based telescopes (not realized by Hubble since it's so close to Earth) is the much longer observing times you can have, viewing a region of the sky for possible days at a time. On Earth's surface you're limited to night-time observations, but in space pointing away from the Sun it's always night.

Re:Evolutionary Step Effect

[William Tanksley]

To what would this hypothetical adaptive space telescope adapt? The adaptive ground-based telescopes adapt to the atmosphere; but there's no atmosphere in space.

I just don't see how adaptive technology could improve a space telescope.

-Billy

You have telescope envy.

[Performer Guy]

Nice shot for a home telescope but it's a small fraction of the resolution on the instrument you chose to compare with, and it can't match the capability of the other instruments on the Hubble. It's downright misleading to draw this comparrison.

Saturn is the easiest object to image, you chose it for a reason. How about some of the feinter objects. Come on show us just how incapable your 13 inch telescope really is with a deep field shot.

Re:Evolutionary Step Effect

[Dyolf Knip]

It couldn't. The solution in space is to make bigger telescopes. This is a big ground-based telescope and it's taking the finest electronics we've got to make it measure up to a much smaller one in space. Remember, gravity isn't an issue up there so, say, a 100 meter lens would be easier to construct and deploy.

Of course, to do that we'd need a developed industrial capacity beyond the clouds, which means we'd need decent launching capabilities. Which means NASA won't have any part of it.