Such sums are almost unheard of in the scientific world, except for a very few big-ticket items. Eventually, the Hubble will be succeeded by a larger instrument called the James Webb Space Telescope (JWST), which will be launched in 2011. That instrument will be very different from its predecessor. It will have a mirror 6.5 metres in diameter, and will work in the infra-red. Moreover, it will ply its trade from a point some 1.5 million kilometres from Earth rather than in low Earth orbit. Nevertheless, its optimistic proponents expect it to be much cheaper than the Hubble.
Both Hubble and JWST are specialised telescopes, and astronomers have always recognised that their wider needs can only be met by building less expensive ground-based instruments. The Hubble's US$2 billion price-tag, for example, would be enough to build twenty of today's largest class of ground-based telescopes. So astronomers have had no choice but to confront atmospheric turbulence head-on.
Some places on Earth tend to suffer more from bad seeing than others. During the 1960s, scientists all over the world embarked on site testing programmes to establish where the best observing conditions could be found, spurred on by a new generation of wide-bodied jets that promised easy access to remote facilities. Before this, telescopes had been built wherever the astronomers happened to bewhich was not always a good spot.
A few places emerged with that rare combination of clear skies, freedom from artificial light and good seeing that is astronomy's Holy Grail. Geography played a vital part. Typically, these places were in middle latitudes (between 20 and 40 degrees north or south of the equator), on mountaintops higher than about 3500 metres (11 500 feet), and near the eastern boundary of an ocean. If the mountain peak was on an offshore island and streamlined with respect to the prevailing wind, so much the better.
In the northern hemisphere, such sites were found in the south-western USA, the Big Island of Hawaii and the island of La Palma in the Canaries. Continental Europe was largely ruled out by its bright lights and indifferent weather. In the south, the peaks of northern Chile and the high Karoo of southern Africa were favoured. Australia, having no high mountains on its western seaboard, could boast no truly excellent sitesalthough the Siding Spring Observatory in central New South Wales is still one of the world's least polluted by artificial light. In recent years, a few other places have shown promise. Antarctica, for example, boasts conditions on the high plateau near the South Pole that are particularly good for observing in the infra-redeven though night only darkens the continent for half the year.
When large telescopes were built on high mountain sites, it was found that the typical seeing was 0.5 to 1.0 arcsecondsgood, but still nowhere near the inherent resolution of the telescopes. Then a promising new technology emerged. It prompted a revolution in the esoteric field of astronomical instrumentation.
By 'instrumentation', astronomers usually mean the auxiliary devices that are attached to their telescopes. In many ways, they are the real tools of the astronomerthe telescopes are merely there to deliver light to them. They range from ultra-sensitive electronic cameras to spectrographsmagical devices that sift the rainbow spectra of celestial objects wavelength by wavelength to reveal vital statistics across the abyss of space.
But during the late 1980s, instrument designers began to promise the impossible. They proposed devices that would cancel out the blurring effects of the Earth's atmosphere, allowing objects to be investigated in unprecedented detail. This celestial conjuring trick would be performed using declassified Star Wars technology known as adaptive optics. Small, deformable mirrors, bending in sympathy with the distortions in the incoming light, would simply cancel out the blurring. Early experiments proved so successful that astronomers began to envisage a time in the not-too-distant future when ground-based telescopes might be limited only by their intrinsic resolution. At last, the curse of atmospheric seeing would be broken. And the participants in 'Power Telescopes and Instrumentation into the New Millennium' were eager to hear the latest on the progress of adaptive optics.
From Stargazer by Fred Watson, pages viii - x of the Prologue, and pages 1-17 of Chapter 1. Copyright Fred Watson. All rights reserved. Excerpt reproduced by permission of Da Capo Press.
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