Friday, 30 March 2012
Red-Hot Chile Peepers
I loved this article from the BBC web site.
To my mind the person who thought up the strap line of - Red-hot Chile peepers - ought to be promoted to Director General off the BBC immediately - for their wit and imagination.
The story itself may be out of this world - but for me the headline is the real star.
"Red-hot Chile peepers: How to make a very large telescope"
By Katia Moskvitch
Telescope goes after first stars
In the hot and desolate lands of Chile's Atacama Desert, seemingly lonely and lost, four huge metallic structures tower over the dusty summit of Cerro Paranal.
Look closer, though, and you will detect a buzz of activity.
The structures have names - Antu, Kueyen, Melipal and Yepun - and each encloses a telescope. Together they form the VLT, or Very Large Telescope, the world's biggest optical telescope facility.
Every now and then, the VLT is in the news, when its astronomers make yet another discovery. Run by the European Southern Observatory (Eso), the VLT became fully operational in 2000.
Since then the telescope has tracked stars moving around the supermassive black hole at the centre of our galaxy, shown us the first-ever images of an exoplanet and captured the afterglow of the furthest known gamma-ray bursts.
The Paranal Observatory offers perfect natural conditions for astronomers: there is virtually no light pollution; the skies are clear; clouds appear on only about 30 days a year. Still, observations would not be the same without the cutting-edge technology of the VLT.
The telescopes are packed with instruments, both above and below ground.
They allow scientists to capture images of stars and nebulas billions of light years away with the clarity you would expect of a snap of your cat snoozing on your living-room sofa.
As the intensely red sun above Northern Chile disappears beyond the horizon, the domes of the four silvery towers slowly open.
They gradually expose the telescopes, ready to eye the night sky and send astronomers valuable data about the Universe.
"Look at this mirror," says Stephane Guisard, an optical engineer at Paranal, pointing at a piece of glass eight metres in diameter. One of the VLT's units is slowly rotating just above our heads.
The type of mirror we have in this telescope is not the same type of mirror you have in your bathroom.
The difference is its optical quality, its smoothness. For example, if it was the diameter of the Earth, it would be so smooth that the biggest mountain would be only a few millimetres high."
This mirror is the main feature of each VLT unit. It is where the light from objects in the night sky first arrives.
But there is no eyepiece for astronomers to peer into to get the final image.
"Once the telescope points at the star we want to observe, the light [from this star] first reflects off the main mirror, which then concentrates it towards the secondary mirror, and then sends it to one of the three instruments of the telescope," says Mr Guisard.
The astronomers will use different instruments for different tasks, depending on what they are looking for.
The VLT is able to link its four units together to create a huge virtual telescope with a much better zoom. Every time an observation takes place, the telescope rotates around both its vertical and horizontal axes.This rotation means spinning around a colossal mass of metal: the total weight of the moving part of the telescope is 450 tonnes.
The main mirror alone weighs 20 tonnes - as much as four pick-up trucks.
Because the rotating structure is so heavy, the telescope distorts - but it is vital for the astronomers to keep the shape of the mirror intact.
"The eight-metre mirror is very thin compared to its diameter. It's optically very floppy. For example, if we were to put it on three points, it would break under its own weight," says Mr Guisard.
"So in order for this not to happen and to keep a perfect shape while the telescope is moving, the mirror is supported by 160 actuators."
A powerful laser beam pierces the atmosphere and creates an artificial star, to help astronomers observe real ones
This mechanism of continually adjusting the mirror is called active optics.
But there is another system that helps astronomers get the best image possible - adaptive optics. Once a ground-based telescope points at a star, it encounters the turbulence of the atmosphere. This turbulence creates the twinkling effect in stars, which makes images blurry.
To correct the distortion, astronomers use a bright reference star located close to the object being observed and measure the blurring. An adjustable mirror then compensates for it.
"Without the adaptive optics, a telescope like one of the VLT units has a no better resolution than a 20cm telescope," explains Frederic Gonte, head of instrumentation at Paranal.
"With the adaptive optics, it is better than the Hubble telescope in space."
Scientists are able to make use of a laser beam so powerful that, once out of the telescope's dome, it pierces the atmosphere.
"The LGS has been developed to compensate for the limitations of the adaptive optics," says Mr Gonte.
"The laser illuminates the sodium layer of the atmosphere, 90km above the Earth, creating an artificial star that we are able to catch with our adaptive optics system and correct for the distortions in the atmosphere."
Now if you followed all that I have to say - 'You're a better man than I am Gunga Din!'
Me - I think I'll just stick to SpecSavers.