Name: 巨型望遠鏡如何工作 (How a Giant Telescope Works)
Uploaded: 2021-01-14T04:59:02.000Z
Duration: 6 min 54 s
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Bigger is better - at least when it comes to telescope mirrors.

But larger mirrors have to be thick, so that they don't deform under their own weight.

And really large mirrors deform anyway, no matter how thick and heavy they are.

The solution? Thin, lightweight mirrors - and a magic trick called active optics.

And this is the state of the art. The mirrors of the Very Large Telescope - the VLT

- are 8.2 meters across... but only 20 centimetres thick.

And here's the magic: a computer-controlled support system ensures that the mirror keeps

its desired shape at all times to nanometer precision.

In the middle of the Atacama Desert, ESO created an astronomer's paradise. Of course, the unique

selling point of the Very Large Telescope is its unequalled view of the Universe.

Without thin mirrors and active optics, the VLT wouldn't be possible. But there's more.

Stars appear blurry, even when observed with the best and largest telescopes. The reason?

The Earth's atmosphere distorts the images.

Enter the second magic trick: adaptive optics. On Paranal, laser beams shoot out into the

night sky to create artificial stars. Sensors use these stars to measure the atmospheric

distortions. And hundreds of times per second, the image is corrected by computer-controlled

And the end effect? As if the turbulent atmosphere were completely removed.

The Milky Way is a giant spiral galaxy. And at its core - 27,000 light-years away - lies

a mystery that ESO's Very Large Telescope helped to unravel.

Massive dust clouds block our view of the Milky Way's core. But sensitive infrared cameras

can peer through the dust and uncover what lies behind. Assisted by adaptive optics they

reveal dozens of red giant stars. And over the years, these stars are seen to move! They

orbit an invisible object at the very center of the Milky Way.

Judging from the stellar motions, the invisible object must be extremely massive. A monstrous

black hole, weighing in at 4.3 million times the mass of our Sun. Astronomers have even

observed energetic flares from gas clouds falling into the black hole. All exposed by

So thin mirrors and active optics make it possible to build giant telescopes. And the

adaptive optics take care of the atmospheric turbulence, providing us with extremely sharp

images. But we're not done yet with our magic tricks.

There's a third one. And it's called interferometry.

The VLT consists of four telescopes. Together, they can act as a virtual telescope measuring

Light collected by the individual telescopes is channeled through evacuated tunnels and

brought together in an underground laboratory. Here, the light waves are combined using laser

The net result is the light-gathering power of four 8.2-meter mirrors, and the eagle-eyed

vision of an imaginary telescope as large as fifty tennis courts.

Four auxiliary telescopes give the network more flexibility. They may appear tiny next

to the four giants. Yet, they sport mirrors 1.8 meters across. That's bigger than the

largest telescope in the world just a hundred years ago!

Optical interferometry is something of a miracle. Starlight magic, wielded in the desert.

The Very Large Telescope Interferometer reveals fifty times more detail than the Hubble Telescope.

For instance, it gave us a close-up of a vampire double star. One star is stealing material

Irregular puffs of stardust have been detected around Betelgeuse - a stellar giant about

to go supernova. And in dusty discs surrounding newborn stars, astronomers have found, the

raw material of future Earth-like worlds.

The Very Large Telescope is mankind's sharpest eye on the sky. But astronomers have other

means to expand their horizons and broaden their views. At the European Southern Observatory,

they have learned to see the Universe in a completely different kind of light.