Starring role: the view from the Very Large Telescope

The VLT sits atop a mountain in the desert in northern Chile, home to some of the darkest skies on Earth – the perfect place to observe our universe and its galaxies billions of light years away

Thu, Jan 23, 2014, 01:00

The first planet detected in orbit around a distant star was not seen by the Hubble Space Telescope. No, this honour goes to the appropriately named Very Large Telescope, the world’s largest and most advanced ground-based optical telescope.

The VLT sits on the 2,600m Cerro Paranal mountain in the middle of the Martian-like Atacama Desert in northern Chile, which is home to some of the darkest skies and most hostile land on Earth. Here, the European Southern Observatory’s flagship facility is perfectly placed to observe our universe and its galaxies billions of light years away.

The VLT, which has been in operation since 1999, comprises four unit telescopes with 8.2m-diameter mirrors, four movable 1.8m-diameter auxiliary telescopes and the Vista survey telescope, which works at infrared wavelengths.

The telescopes can see objects four billion times fainter than can be detected by the human eye. They are responsible for the first image of an extrasolar planet, as well as the tracking of individual stars moving around the massive black hole at the centre of the Milky Way.

On the day I arrive, I am lucky enough to see one of the mirrors being removed from a telescope to be recoated at a maintenance building nearby. “This procedure requires lot of precision,” says optical engineer Guillaume Blanchard. “It gets recoated every 18 months, because dust collects on the surface and it degrades the quality of the astro observations.”

The mirror, which weighs 23 tons, gets brought to the biggest dishwasher in the world, where the old coating is removed with acid. After a washing process, it gets coated in particles of aluminium. The mirror itself is thinner than a hair, the rest made of a ceramic plate that doesn’t expand in heat.

I get a tour of the telescopes and then, at sunset, stand inside to watch the roof open and the mirror turn towards the sky, escorted by my guide, Farid Char. In Paranal you get an average of 320 clear nights per year, with an average of 5-10 per cent humidity. Near-perfect conditions.

But what about earthquakes, I ask. “Even though it sits on a fault, the VLT can withstand an earthquake of big proportions,” he says. Research suggests it can withstand up to seven on the Richter scale without damage, and more than eight with only minor cosmetic damage.

The opening process takes about 30 minutes, in which time the sky turns from deep tangerine to lilac. Eventually it becomes black, and then the stars and the astronomers come out for the night.

“The VLT collects more light than the Hubble, which has a 2.5m diameter compared to our 8.2m,” says Zahed Wahhaj, an astronomer working at the VLT.

Munich-based astronomer David Wilman is researching galaxy formations. “We are observing a new star. It’s over 10 billion light years from Earth.” So it’s an old star then? “Well you are looking 10 billion years back into the past. At that time it was only three billion years since the big bang. So it would be old. Very old.”

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