A Telescopic Behemoth

by Nicholas Mee on June 25, 2014

The Starry Messenger

It is just 400 years since Galileo first pointed his telescope at the night sky – a mere five lifetimes ago. His enhanced view of the heavens brought about a revolution in our understanding of the universe.

Everywhere Galileo looked he made new discoveries. He found that the Moon was mountainous and cratered. He saw Venus as a crescent. He saw sunspots on the Sun and a myriad stars in the Milky Way. His most spectacular discovery was the existence of four moons dancing around that planet Jupiter. Galileo raced to get an account of his discoveries into print in a booklet called Siderius Nuncius (The Starry Messenger), which appeared early in the year 1610.  His sensational new view of the cosmos would overthrow the traditional understanding of the heavens and open the way for a transformation of astronomy.

In the centuries since Galileo every step onwards in our technology for viewing the heavens has generated dramatic discoveries. The improvements in equipment in recent decades has been incredible. We are currently living through a golden age of astronomical research.

Desert Astronomy

The European Southern Observatory (ESO) is funded by 14 European nations making it the most important inter-governmental body for astronomical research. The photograph below shows the site of ESO’s Very Large Telescope complex (VLT) which has been constructed at an altitude of 2,400 metres on a mountain top at Paranal in Chile. This site was chosen as it is within one of the driest regions on Earth – the Atacama desert. The incredibly low humidity and high altitude give the night sky an extra clarity, dramatically reducing the blurring effects of turbulence in the atmosphere above the observatory. The VLT is the most advanced optical observatory in the world. It consists of four main telescopes, each of which has an 8.2 metre diameter mirror, along with four 1.8 metre auxiliary telescopes.

The Very Large Telescope complex in the Chilean Andes (c) ESO.

The four main telescopes are named Antu, Kueyen, Melipal and Yepun. These are the names of four celestial objects in the local Mapuche language. Antu means Sun. Kueyen means Moon. Melipal means Southern Cross and Yepun means Venus. Antu was the first of these telescopes to come into operation in April 1999.

Adaptive Optics

Even in the almost ideal setting of an Andean mountain top there is still some atmospheric distortion of the starlight gathered by the huge telescope mirrors. To compensate for this distortion the VLT telescopes use adaptive optics. A laser is fired into the night sky. It reflects from the upper atmosphere to produce an artificial point of light or guide star. This guide star is then viewed through the telescope and a computer controlled feedback mechanism continuously deforms the mirrors of the telescope to keep its image sharp. The mirror deformation mechanism compensates for any fluctuations in the atmosphere and enables the telescopes to produce images that are much sharper than would otherwise be possible, rivaling a much more expensive space-based telescope.

In addition the four main telescopes and the four auxiliary telescopes can be operated as an interferometer in which the light from the telescopes is channeled through underground tunnels and combined to form an ultra-sharp image of incredibly high resolution.

The results are spectacular, as the image below demonstrates. This image shows a star-forming region in the dwarf galaxy companion of the Milky Way known as the Large Magellanic Cloud. The nebulae in the image have been produced by intense stellar winds from extremely hot new-born stars.

Star-forming region in the Large Magellanic Cloud (c) ESO.

The European Extremely Large Telescope

The European Southern Observatory has just started the construction of what will be by far the world’s largest telescope. The new behemoth will be known as the European Extremely Large Telescope (E-ELT). The site is on a mountain top twenty kilometres from the VLT complex, at an altitude of just over 3,000 metres. The composite mirror of the telescope will be constructed from 798 hexagonal segments, each 1.4 metres wide, making the full mirror a gargantuan 39 metres in diameter. This will enable the telescope to collect about 15 times as much light as any existing telescope. The telescope will incorporate an advanced adaptive optics system using several lasers and actuators that can distort the shape of the mirrors a thousand times each second.

The E-ELT will begin operation at the start of the next decade. Every advance in optical equipment has brought sensational discoveries about our place in the universe and the same will surely be true of the E-ELT. It will give astronomers the ability to search for the first generation of stars in the very early universe, it will enhance the search for Earth-like planets around distant stars and it will enable astronomers to probe the supermassive black hole at the centre of our galaxy, but it will also reveal the unexpected.

An artist’s impression of how the E-ELT will look when completed (c) ESO.

 Further Information

More information about the European Southern Observatory and its telescopes is available on ESO’s website at: European Southern Observatory

If you are interested in the history of astronomy from Galileo’s telescope to the supermassive black hole at the centre of our galaxy, take a look at my book Gravity: Cracking the Cosmic Code.

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