OT: Hubble photos in movie form

No - never able to do most of this from the ground. The 'air' above us filters so much of the light and the general glow of the earth reflecting within this outer shell prevents most.

The angular precision is way beyond ground at this time.

The largest one being built on Hawaii now IIRC, KECK ? - will be fantastic, but not Hubbell.

What we really want is Keck on the moon - or Hubbell on the moon. Now that would be thin space to look through.

Martin

Reply to
Eastburn
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In fact, Keck I, which has been operating since 1993, surpasses Hubble in angular resolution. 0.02 arc second for Keck I, 0.05 arc second for Hubble at 570 nanometer wavelength. Keck I's

10 meter primary mirror also gathers much more light than Hubble's 2.4 meter mirror (approximately 100 times more), and since it is actually correctly figured, unlike the Hubble mirror, all of that light is usable.

In 1997 Keck II came on line. It is also a 10 meter mirror. In 2002 it was coupled to Keck I to make the largest inferometric optical astronomical system in existance, with a resolution 100 times better than either telescope alone. It has been used to view the transit of Jupiter size planets in other solar systems, and it has provided the best surface maps we have of the other planets and moons in our solar system.

Atmospheric distortions are minimized by the telescope's location, high on a mountain surrounded by thousands of miles of ocean. This homogeneous thermal environment means it is about the best location on Earth for minimizing atmospheric turbulence. And in

1999 adaptive optics were added to Keck which automatically correct for the remaining atmospheric abberations.

The adaptive optics system uses the artificial guide star principle, and a "rubber" secondary mirror which is capable of changing shape

670 times a second under servo control (the timescale of the quickest atmospheric thermal cells, which cause "twinkling", is about 100 times slower than this, so the system has more than sufficient bandwidth).

Note that Harvard now runs another pair of 10 meter telescopes in the Andes, giving a view of the far southern sky which Keck can't see. It's scopes do have more atmospheric turbulence to overcome, because they are located in a mountain *range* rather than on an isolated volcanic mountain in the middle of an ocean, but they are also fitted with adaptive optics adequate to the job.

The one place where Hubble excels with respect to Earth based telescopes is in the UV. The atmosphere (ozone layer) blocks UV from reaching the surface. So Hubble has an advantage when observing in the UV by being located above the atmosphere.

That's where off Earth telescopes shine, for viewing parts of the EM spectrum blocked by Earth's atmosphere. UV, X-ray, and gamma ray telescopes have to operate outside Earth's atmosphere. But the atmosphere is no longer the big issue for telescopes operating in the visible spectrum.

OTOH, Hubble cost in excess of $1 billion dollars to build, $500 million to launch, and $500 million twice more to service (with one more $500 million service mission still yet to go, which may or may not happen now depending on the flight rules Shuttle will have to observe when it returns to flight).

By comparison, Keck I cost $154 million to build, and is serviced daily by shirt sleeved men in Jeeps costing about $20,000, and using about $5 worth of gas per trip. In other words, we are getting one hell of a lot bigger bang for the buck from Keck than we ever will from Hubble.

Note, Hubble was designed in the 1970s, built in the early 1980s, and was finally launched in 1990. Much of its technology is dated compared to Keck and its siblings, and is *much* harder and more expensive to update. Consequently, NASA already has plans to decommission and deorbit Hubble by the end of this decade. Keck will likely still be in use for many decades to come.

Gary

Reply to
Gary Coffman

What I don't understand is, where are the Keck pictures of the same objects that Hubble is famous for discovering? The Hubble pics Spehro pinted to are mostly the same ones I saw a few years ago.

And what do they use for an "artificial guide star"? A satellite?

Reply to
Tom Del Rosso

Most likely they use a sodium vapor laser and create an artificial guide star in the thin upper atmosphere.

Cheers!

Chip Shults My robotics, space and CGI web page -

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Reply to
Sir Charles W. Shults III

Keck doesn't have the PR machine that NASA has. But if you check some of the astronomical journals you'll find plenty of pictures taken by Keck.

They use the backscatter from a laser which they fire coaxially with the telescope. Since the beam passes through the same air whose motions they're trying to compensate, when they compensate the known beam, they've compensated all the atmospheric errors.

Gary

Reply to
Gary Coffman

Thanks Gary, Chuck.

Reply to
Tom Del Rosso

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