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Tuesday, 4 December, 2001, 17:05 GMT
Telescope now 'as good as Hubble'
VLT image
This view from a ground-based telescope at Paranal...
By BBC News Online science editor Dr David Whitehouse

A ground-based telescope has taken pictures of stars that match the quality of those provided by the Hubble Space Telescope (HST) in orbit.

Star seen from Hubble Space Telescope of similar quality to this one from Hubble
A team of astronomers and engineers at the Paranal Observatory in South America used a new Adaptive Optics (AO) facility to counteract the distorting effects of the Earth's atmosphere that make stars appear to twinkle when viewed from the ground.

The result is images that are just as sharp as the ones HST can get sitting high above the planet's turbulent gases.

"I am proud of this impressive achievement," said European Southern Observatory Director General Catherine Cesarsky.

Sharpest image

AO works by means of a computer-controlled flexible mirror.

The system looks at a reference star to determine how much atmospheric turbulence there is. It then sends commands, 500 times a second, to the mirror to counteract that distortion.

The AO system was connected to the 8.2-metre Yepun telescope during a four-week period of installation and commissioning. Yepun is the fourth and final telescope which makes up the Very Large Telescope (VLT) complex at Paranal.

On 25 November, light from a star bounced off the computer-controlled deformable mirror and formed the sharpest image produced so far by one of the VLT telescopes.

Even sharper

With an apparent diameter of only 0.07 arcsec, this image is near the theoretical limit possible for a telescope of this size.

Paranal Observatory, ESO
There are four telescopes making up the VLT complex at Paranal
Catherine Cesarsky said: "It shows the true potential of European science and technology and provides a fine demonstration of the value of international collaboration.

The European Southern Observatory (which operates Paranal) and its partner institutes and companies in France and Germany have worked a long time towards this goal - with the first, extremely promising results, we shall soon be able to offer a new and fully tuned instrument to our wide research community."

The sharp images were obtained just four weeks after "First Fringes" were achieved for the VLT Interferometer (VLTI), which consists of two of the 8.2-m telescopes at Paranal linked together.

This linking technique can produce even sharper images than that produced by the AO method.

See also:

25 Mar 99 | Sci/Tech
Far-sighted telescope opens eyes
22 May 01 | Sci/Tech
When the Universe was 'spongy'
23 Nov 00 | Sci/Tech
Observatory coup for UK astronomers
07 Dec 01 | Sci/Tech
Telescope snaps 'perfect spiral'
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