The Great
Telescope Race
Astronomers around the world are competing to build the world's most powerful telescope.
Their designs range from a supersized Hubble Space
Telescope to the world's biggest pair of binoculars - and a telescope as big as a football pitch.
by Nigel Henbest
High above the Earth, a gargantuan telescope peers into space. It dwarfs the Hubble Telescope, the twentieth-century's greatest scientific instrument. With a mirror half the size of a tennis court, the Next Generation Space Telescope will reveal the edges of the observable Universe.
The Next Generation Space Telescope is already on the drawing board. Within 10 years, this ultimate telescope will be flying in space. Instead of orbiting the Earth, the Next Generation Space Telescope will follow its own orbit around the Sun. But its designers will place it at a special balance point, outside Earth's own orbit. At this location, the so-called Lagrangian-2 point, our planet's gravity still ensnares the telescope, so it travels round the Sun always a million miles from the Earth.
Huge solar panels will provide the telescope with power, and - just as important - shield it from the Sun's heat. Cooled down to the temperature of deep space, the Next Generation Space Telescope can observe faint heat signals from the farthest reaches of the Universe. It will peer beyond where even Hubble can see, to the very edges of the observable Universe.
Because light takes billions of years to travel this far, the Next Generation Space Telescope will be seeing these distant regions as they were billions of years ago - just after the Big Bang in which everything began.
This ultimate telescope combines the clear views that Hubble enjoys with the mammoth size of the biggest
telescopes currently being built on the ground.
In the dry deserts of Chile, astronomers are this year completing the most powerful telescope ever constructed on Earth. The Very Large Telescope in fact comprises four telescopes, on the peak of a mountain that has been blasted flat to form a platform for the cosmic quartet. Each of the telescopes has a mirror 8 metres (26 feet) across. Linked together, the four instruments will collect as much light as a single telescope over 50 feet in size.
Three of the four telescopes are already working, and astronomers have been astounded by the quality of their views of the cosmos - of glowing nebulae, dying stars and distant galaxies.
To construct such a vast telescope, its builders have pushed engineering to the limit. In particular, the telescope must tilt to turn to different galaxies, giving gravity a purchase on its huge - but thin - mirror. If gravity bends the mirror by an amount smaller than the width of a human hair, the telescope's view of giant galaxies is blurred to uselessness. So the designers have attached the back of the mirror to hundreds of moving supports, computer-controlled to push the mirror back into shape - a millionth of an inch at a time - as the telescope tilts.
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 ethe 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.
The Next Generation Space Telescope will combine Hubble's sharp views with the power of today's large telescopes on Earth. And so, some astronomers are moving on to dream up even bigger instruments that could be built on terra firma. The most audacious plan of all the OverWhelmingly Large Telescope.
The OverWhelmingly Large Telescope - OWL for short - would have a mirror 100 metres across. That's as big as a radio telescope like Jodrell Bank or the Green Bank radio dish in West Virginia. In everyday terms, we're thinking not so much of a tennis court but of a football pitch.