Is the Hubble Telescope Obsolete?

[Thecla]

Some years ago I read that the Hubble Telescope is obsolete because modern telescopes have adaptive and corrective optics that make a space telescope unnecessary(at least for visible light). Since new Earth based telescopes have the advantage of very large mirrors(10 meters for the Keck) vs 2.4 meters for the Hubble, their ultra deep image of a random small area in the sky that shows thousands of galaxies must be specacular compared to the Hubble's iconic image. I haven't seen this photo. Are there photos that compare Hubble with a Keck?

 

[turbo]

HST is heavily over-subscribed, so it is not obsolete by any means. All kinds of astronomers are lined up hoping for time on that instrument.

 

[Super Luminal]

It is obsolete in that its individual components are no longer cutting edge technology. But, you must remember that it has been in space for over 20 yrs. But, by that definition virtually all pieces of tech become obsolete very quickly as new, better designs and improvements are always seemingly around the corner, so to speak. So the Hubble Space Telescope is, then, functionally obsolete. But is still works. It is continuing to provide us with new and exciting discoveries. And as the poster above me said, scientists still want to use the thing.

 

[twofish-quant]

Some years ago I read that the Hubble Telescope is obsolete because modern telescopes have adaptive and corrective optics that make a space telescope unnecessary(at least for visible light).

There is some truth in that, which is why a lot of the time spent using Hubble are focused on observations in the near-UV. Without near-UV observations, things like the high-Z supernova that discovered the expanding universe would be difficult to impossible. The trouble is that you have spectral lines that are UV in some redshifts and visible in others, and if you don't have a telescope that can scan everything between near-UV and visible then it's hard to match spectral lines.

Since new Earth based telescopes have the advantage of very large mirrors(10 meters for the Keck) vs 2.4 meters for the Hubble, their ultra deep image of a random small area in the sky that shows thousands of galaxies must be specacular compared to the Hubble's iconic image. I haven't seen this photo. Are there photos that compare Hubble with a Keck?

They really aren't for an interesting reason. Essentially both Hubble and most large telescopes can see galaxies to the big bang, so if you have a more sensitive telescope, you might pick up some small dimmer galaxies, but those aren't going to look very impressive. Also a lot of these young galaxies shine mainly in blue/near-UV so if you block out the UV spectrum, the pictures look less impressive. (Your eyes can't see UV, but cameras can.)

There are other issues. I don't think that the resolution of galaxies is at the limits of Earth telescopes. Finally adaptive optics works a lot less well if you are looking at a large field. If you are looking at one star, then you can wiggle the lens to remove distortion for that one star easily. If you are looking at ten thousand galaxies across a large patch of space, then it becomes difficult (maybe impossible) to use adaptive optics, because different parts of the picture require different corrections.

A lot of astronomical photography is like any sort of photography in that there is as much art as science. For example, if you want cool looking spiral arms, you want to be most sensitive in blue so that you pick up the hot young stars.

 

[dschlink]

Also consider that several instruments have been upgraded or replaced with better devices. Two new instruments, Wide Field Camera 3 (WFC3), and the Cosmic Origins Spectrograph (COS) were installed in 2009. WFC3 has 35 times the data gathering capacity.

 

[Thecla]

O.K. Let the Keck look at a small region of the sky. It would be an interesting comparison

In this corner, the Keck: Advantage: 10 meter diameter, adaptive optics, latest technology
Disadvantage: the atmosphere

In the opposite corner, the Hubble: Advantage: vacuum of space
Disadvantage:mirror only 25 % of the diameter of the
Keck, difficult to upgrade technology

Rules : Limit region to very small area of the sky to accommodate the Keck
Limit exposure to 8 hours also to accommodate Keck.


The reason I created this thread is that most of the spectacular images seem to come from Hubble, nothing from ground base telescopes.
It make you wonder that if there were a 100 meter mirror on an Earth based telescope,its performance would still be inferior to the Hubble.

 

[phinds]

to summarize: obsolete does NOT mean useless by any stretch

 

[Drakkith]

I think that if you can correct for aberrations enough to reach "diffraction limited" status, both telescopes are equal if all else is the same. That said, a bigger mirror gathers more light and has a smaller airy disc, so other than extinction of the light by the atmosphere, light pollution, and the motion of the Earth the bigger mirror may win out over the Hubble. But this is only for light that can reach the ground. If what you need to image cannot make it through the atmosphere then obviously the Hubble would win out easily. I'm not sure on whether the Hubble sees into ranges that don't make it through the atmosphere though.

 

[twofish-quant]

Also consider that several instruments have been upgraded or replaced with better devices. Two new instruments, Wide Field Camera 3 (WFC3), and the Cosmic Origins Spectrograph (COS) were installed in 2009. WFC3 has 35 times the data gathering capacity.

One thing about Hubble is that it was designed with the assumption that manned upgrades would be cheap and easy. This turned out not to be the situation, and so all of the next generation telescopes are designed to be non-upgradable with the assumption that if there is a problem you can throw up another telescope.

The problem with manned upgrades is that it turns out that manned space flight is extremely dangerous so if you have to send up a shuttle to fix something, then you have to get into huge arguments over whether or not it's desirable to risk human life to fix something.

One advantage of ground based telescopes is that you have to deal with fewer politicians to build them.

 

[twofish-quant]

The reason I created this thread is that most of the spectacular images seem to come from Hubble, nothing from ground base telescopes.

There's a political reason for this. Most of the funding for the space-based telescopes comes from tax money so there is a very strong pressure to create some cool pictures so that people can see where their tax money is going. By contrast, most ground-based telescopes get their funding from private foundations, and what tax money there is is indirect. So there's less of a need to create "pretty pictures".

Creating "pretty pictures" takes up time that could be used for other things, so people aren't going to do it unless there is a strong reason to do it.

It make you wonder that if there were a 100 meter mirror on an Earth based telescope,its performance would still be inferior to the Hubble.

If one type of telescope were better for everything then we'd use only that one type. It turns out that each telescope has it's strengths and weaknesses.

 

[Chronos]

The Hubble is the 800 pound gorilla of telescopes. Do 800 pound gorillas become obsolete?