The Great Telescope Race

While telescopes in Chile are placed to view the southern sky, the best place on Earth for observing the northern heavens is the 14,000-foot high peak of Mauna Kea, Hawaii. Here, astronomers have constructed the world's biggest astronomical observatory. Put together, the total area of the mirrors in these telescopes would outstrip even the Very Large Telescope. But these instruments are competitors, each seeking to be the most powerful telescope observing the northern part of the sky.

Gemini North is the latest, starting work this year. The surface of its mirror is so smooth that if you enlarged it to the size of the Earth, the largest bump would be only a foot high. Next door is the Japanese telescope Subaru, with the biggest single mirror in the world - almost 8.3 metres (27 feet) across. Like the Very Large Telescope, it has hundreds of supports, actively pushing the mirror into the precisely correct shape.

But the jewels in the crown of Mauna Kea are the pair of Keck Telescopes. Each has a mirror 10 metres (33 feet) across. No-one could manufacture a single piece of glass that size, so the Keck mirror is made of 36 pieces, each just six feet across, fitted together like bathroom tiles. A perfect fit between the tiles is ensured by a computer-activated system, pushing on the back of each segment to ensure the tiled mirror forms a single perfectly smooth surface. To spread the forces evenly, the support system is based on a design used to even out the force of horses pulling a Wild West covered wagon!

The first Keck telescope has been observing for eight years, and it has revolutionised astronomy, from discovering tiny ice planets beyond Pluto, to tracking planets of other stars - and pinning down the distances to the farthest known galaxies, over 10 billion light years away.

Texas has an even bigger panelled telescope, the Hobby-Eberly Telescope, some 12 metres (almost 40 feet) in diameter. Its design has brought it in at only one-tenth the cost of Keck, with the payoff that it cannot focus quite as accurately. Its strength, instead, will come from splitting up the light from distant objects in more detail than any other telescope.

On Mount Graham, in Arizona, the world's 'biggest binoculars' are about to peer at the sky. The Large Binocular Telescope has two giant mirrors - each 8.4 metres (27 feet) across - mounted on the same frame. But astronomers here have decided against the complication of using hundreds of computer-controlled supports to keep the mirror in shape.