Supertelescope to cast an eye on distant worlds and seek origins of the universe

They call it the Planet Machine. Weighing 1,000 tons and standing as tall as an 18-storey building, the world's biggest optical telescope is designed to see where no-one has seen before.

It has been a gleam in the eye of astronomers for nearly a decade and now they are on the verge of seeing the birth of their brainchild - a telescope that for the first time will enable us to watch other Earth-like planets orbit distant suns.

The Giant Magellan Telescope (GMT) will be four times bigger than the biggest existing telescope and 10 times more powerful than the hugely successful Hubble Space Telescope.

It will use computer optics to eliminate atmospheric interference so that from its mountaintop perch in the bone-dry Atacama desert of Chile it will see further than any terrestrial telescope into the depths of time and space.

In addition to seeing "exoplanets" beyond our Solar System, the telescope could quite literally shed light on some of the biggest mysteries of the universe, from the origins of creation to what might happen if time itself comes to an end.

The Australian National University announced this week that it is the latest partner to sign up to the consortium of nine institutions dedicated to building the GMT at a total estimated cost of £310m.

The largely American consortium is being led by the Carnegie Institution of Washington which built one of the first large telescopes at the beginning of the 20th century that led the great American astronomer Edwin Hubble to discover that the universe was expanding.

Now astronomers know that the universe is not just expanding, it is expanding at an accelerating rate, propelled by a mysterious force they have dubbed "dark energy".

By building a telescope with seven huge mirrors acting in perfect unison, astronomers believe they can capture images to understand both dark energy and dark matter - the equally mysterious "missing mass" of the universe that cannot be seen with conventional telescopes.

"We all share a common goal of probing the most important questions in astronomy facing us over the next generation," said Wendy Freedman, director of the Carnegie Observatories and chair of the GMT board.

"The mysteries are dark energy, dark matter, and black holes; the birth of stars and planetary systems in our Milky Way; the genesis of galaxies, and much more," Dr Freedman said.

So far the consortium has raised just £9.5m towards the cost of building the GMT but it has already promised the funds to build the first of seven giant mirrors, each of which will be 8.4 metres in diameter. Roger Angel of the University of Arizona, who is in charge of manufacturing the mirrors, said yesterday that the first mirror had already been "cooked" at 1,165C in a slowly spinning centrifuge furnace. It will now go through two years of grinding and polishing.

Each mirror will be made from 20 tons of molten glass and has to be polished to the finest specifications - to within 0.000001 of an inch. This is equivalent to making a perfectly flat surface the size of the United States with nothing sticking upwards from it any higher than a golf ball.

To make matters even more complicated, the parabolic mirrors have to be "off axis", meaning that the light that they reflect is reflected slightly to one side. This is to accommodate the effect of putting seven mirrors side by side.

"Testing the first mirror is in many ways the most critical step because these mirrors go considerably beyond anything that has been made before," Dr Angel said.

Once all seven mirrors are in place they will have an effective collecting area equivalent to a telescope measuring 24 metres across - four times bigger than the biggest so far made.

Laser beams directed into the sky will gauge the level of atmospheric turbulence - which causes stars to twinkle - and enable computer-controlled motors to make ultra-fine adjustments to the surface of each mirror to eliminate optical interference.

Another problem to be addressed is wind. "When you put a big telescope mirror the size of a spinnaker on top of a mountain with the wind blowing, you want to hold its shape to one millionth of an inch," Dr Angel explained.

But perhaps the biggest problem will be raising the hundreds of millions of dollars needed to finish the project by 2015.

"I'm feeling pretty good about that," Dr Angel said. "Carnegie would not be putting money into this if it thought the extra money could not be found. There is a long history in the US of telescopes being funded privately."

The project, however, does have its rivals. Europe has its own plan for a super-sized telescope, as does at least one other consortium in America.

So the race is on to build the next generation of supertelescope. "The stakes could not be higher," says the science magazine Discover. "Whoever builds the next giant telescope will own the cutting edge of astronomy for years, perhaps decades. Those astronomers and only those will have first crack at the very biggest questions out there."

Looking back

Galileo Galilei is credited with being the first person to use the telescope in astronomy when in 1609 he used a rudimentary device to study the craters of the Moon. He went on to discover sunspots, four of the larger moons of Jupiter and the rings of Saturn.

The precise origins of the telescope are more in doubt. Hans Lipperhey, a spectacle maker working in the Netherlands, may not have been the first to make a telescope but he was the first to bring it to popular attention.

In 1704 Isaac Newton, the great English physicist, introduced the concept of using curved mirrors to replace ground glass in the design of telescopes but it was not until the early 20th century that huge telescopes came into vogue.

The Carnegie Institution built the Hooker telescope in 1917 at the Mount Wilson Observatory in California. Measuring 100 inches across, the telescope remained the biggest for 30 years and was used famously by Edwin Hubble to discover galaxies beyond our Milky Way and an expanding universe.

In 1948, the Hale telescope of the California Institute of Technology took up the mantle of the biggest observing machine. It remained the largest refracting telescope in the world until 1993.

Then came the twin Keck telescopes built on top of Mauna Kea volcano of Hawaii. Each telescope's primary mirror measured 10 metres across, with a mosaic of 36 ultra-smooth, hexagonal segments.

Europe's Very Large Telescope (VLT) on Cerro Paranal, Chile, is made of four observing instruments each eight metres across. It was completed in 1999 and used to study objects such as supernovae or quasars. There are plans to turn the VLT into an even bigger instrument that would combine four telescopes into a single light-gathering observatory.

The Hubble Space Telescope is by these standards relatively small but the instrument benefits immensely from being free of the optical interference caused by the Earth's atmosphere. But the biggest single telescope mirror belongs to the Japanese-built Subaru telescope, also on Mauna Kea in Hawaii.

This instrument was completed in 1999 and has a single-piece mirror measuring 8.3 metres in diameter which took seven years to fabricate and polish. The Subaru uses 261 robotic "fingers" to gently push and pull the mirror as part of a computer-controlled system of adaptive optics.