These three thingsa fixation with ground-based optical telescopes, an obsession with size and a feverish excitement at the prospects for adaptive opticswere the basic ingredients that fermented together in the warm lecture theatres of Munich's International Congress Centre.
Placing them against the backdrop of the telescope's progress over the previous hundred years, it is easy to see why they made such a potent brew. At the turn of the twentieth century, a telescope with a mirror 1.5 metres (60 inches) in diameter was considered large. In 1918 came a 2.5 metre (100 inch) telescope and, by 1948, a 5 metre (200 inch) was ready for work. But of greater significance than these individual achievements was the proliferation of 4-metre class telescopes during the 1970s and early 1980s. Eight of them around the world provided flagship tools for a new generation of astronomers. They revolutionised our understanding of the Universe, expanding its known horizons by billions of light-years and populating it with exotic new objects: neutron stars, black holes and quasars.
In Munich, though, new benchmarks were being laid down. Technology had moved on since the 1970s, and engineers had learned how to make bigger telescopes. Then, a state-of-the-art mirror for a 4-metre class telescope had been a thick, inert slab of glass-ceramic material that relied on sheer bulk to maintain the profile of its reflective front surface. But now computer-controlled mechanical fingers could hold much thinner mirrors in shape, no matter what angle the telescope was pointing at. And the mirrors didn't have to be made of a single piece of glass; they could be segmented from many smaller, hexagonal pieces held in precise alignment by the same sort of intelligent control.
With lighter mirrors came lighter telescope structures and a spidery appearance that belied their inherent rigidity. Enclosure design became vastly more sophisticated than the simple domes used previously, allowing air to flow freely and smoothly past the telescope without causing local turbulence. And improved control systems promised telescopes that could be pointed at their targets with sub-arcsecond accuracy. With all these developments, the stage was set for a repeat performance of the 1970sonly this time with 8-metre class telescopes.
An 8 metre mirror is huge; it is the size of a suburban backyard. Its reflective surface has to be of such sublime perfection that if the mirror could be magnified to the size of the Earth, the biggest irregularity would be no higher than a doorstep. That is one reason why the price of an 8-metre class telescope approaches US$100 million, and why multinational consortia have to be formed to build them.
In the decade 19942004, no less than ten ground-based telescopes with 8 to 10 metre mirrors would be completed. One of these instruments actually contained two 8 metre mirrors; another incorporated four. Three more telescopes with 6.5 metre mirrors were under construction. This was a veritable explosion of telescope-building. And the participants in the Munich symposium sensed, with some justification, that they were at its epicentre. The meeting highlighted the world's burgeoning suite of 8-metre class telescopes and the leap in light-collecting area and focusing power they presented to astronomers: power to observe celestial objects fainter and more remote than ever beforeobjects 'close to the edge of the Universe', as the tabloid newspapers were wont to put it.
But therein lay the controversy. For if these new telescopes were to be so effective in unlocking the secrets of the sky, what was the point in maintaining the old ones? Shouldn't the 4-metre class telescopes be consigned to museums in the face of the new machines? Or, at least, demoted to second-rank instruments with minimal supportparticularly those on poor observing sites . . . ?
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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