Two eyes on the sky

January 8, 1999

Observatories and jobs were sacrificed to build twin giant telescopes, but was it all worth it? asks Alison Goddard

In coming days the first of two giant telescopes will open its eye on the heavens. The Gemini twin telescopes will be the first to provide complete coverage of both the northern and southern hemispheres of the sky, so that astronomers can continuously monitor interesting objects such as baby stars and black holes.

The first telescope is situated at the summit of Mauna Kea, a dormant volcano on Hawaii. Its twin, which will be completed later this year, is on Cerro Pachon, an extremely dry mountain top in the Chilean Andes.

It is 20 years since British astronomers had the idea of building a large telescope in collaboration with the United States. Since then the project has grown to include a second telescope and five more partners: Canada, Chile, Australia, Argentina and Brazil. The United Kingdom has paid a quarter of the total $190 million price tag. "Gemini is designed to give the sharpest deep view of the universe that we can get," says Roger Davies of the University of Durham, who chairs the UK Gemini steering group.

Exciting stuff, yet the UK has paid a high price to take part - the closure of the Royal Greenwich Observatory in Cambridge, announced in July 1997. Much of the work to develop instruments for the Gemini telescopes was done at Cambridge and the Royal Observatory, Edinburgh. But the Particle Physics and Astronomy Research Council was forced to close the Cambridge observatory to pay for Gemini's operation.

Malcolm Longair, president of the Royal Astronomical Society, wrote to members in April 1997: "(The financial) pressures come at a time when Gemini is nearing completion and provision has to be made for the UK share of operations and development. Further cost savings, or programme reductions, are therefore essential. Much of the burden must inevitably fall I on the future workload of the Royal Observatories."

The Cambridge observatory closed at the end of October with the loss of about 50 staff. Five transferred to a new astronomy technology centre created at the Royal Observatory Edinburgh to develop instruments for telescopes. "It is hard to see how you can afford to have a team just ready and waiting to develop telescopes," admits Pat Roche of the University of Oxford, the UK project scientist on Gemini. "As telescope projects get bigger and more international, they will pull in big teams of people as they need them," he adds.

British astronomers are convinced that Gemini will be worth it. "Gemini is critically important for the UK, to allow us to continue at the forefront of ground-based astronomy," Roche says. They are confident, too, that they will still take part in large international collaborations. "It is not necessarily obvious that we can scale up Gemini," says Davies, "but it is very likely that, in future, there will be international collaborations to build mega-telescopes and bigger interferometers."

The bigger interferometers - networks of telescopes that are linked to become, in effect, one huge telescope - will include the large millimetre-wave array. This is an international project to build a linked array of 50 to 100 carbon-fibre dishes for highly sensitive studies of star formation and galactic evolution.

"The large millimetre-wave array is the highest priority for UK ground-based astronomy," Roche says. But astronomers were disappointed with their recent funding allocation, which left particle physics and astronomy with almost static funding for the next three years in real terms. Some planned projects will have to be axed. British physicists must decide whether to participate in the large millimetre-wave array within the year.


The Gemini telescopes are big, with circular mirrors to collect starlight that are eight metres across. This means that the telescopes can see distant faint objects but it also makes them too large to be launched into space. Instead users must peer through the atmosphere, which distorts and absorbs light, blurring the images.

To counteract this, the telescopes have been built on top of high mountains - Mauna Kea and Cerro Pachon are 4,200 metres and 2,715 metres above sea level respectively. Both sites have good weather and are very dry - water absorbs the infrared radiation that the telescopes need to detect. The telescopes will also use a new technology called adaptive optics to straighten bent starlight.

Unlike light, infrared radiation can penetrate the dusty nurseries where stars are born. Astronomers will therefore use Gemini to study star formation. "We know that stars form in dense clouds of dust within our galaxy," says Roger Davies of Durham University. "But if we are really going to understand how stars form, then we can't only look within our own galaxy, we must also look elsewhere. We would really like to know how stars form in galaxies other than the Milky Way."

Gemini will also help astronomers understand how galaxies form and evolve. Because the universe is expanding and light travels at a set speed, looking at distant objects is equivalent to looking back in time. "We can look at galaxies as they were five to ten billion years ago," says Davies. This will allow astronomers to test the theory of hierarchical clustering, which says that dwarf galaxies formed from denser regions and that these amalgamated with neighbours to become galaxies of the normal size that we see today.

Finally, Gemini will be used to test models of how planets form from discs of dust orbiting stars.


"It was the 1987 supernova," says Pat Roche of Oxford University. "It provided the first opportunity to look at a supernova in detail. We made observations using the Anglo- Australian telescope for about two years from shortly after the supernova went off. I was in the UK but I went to Australia every two to three months to pursue these observations."


"It is tremendously exciting to look through a telescope and see the moons of Jupiter and then look a few hours later and see that they have moved," says Davies. "And there are rare events that astronomers see just because they spend a lot of time watching the sky: fireballs and flashes."

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