LO WOLTJER’S TELESCOPE; THE VLT

Francis Bacon, a very wise old bird, wrote; “By far the greatest obstacle to the progress of science and the undertaking of tasks and provinces therein is found in this — that men despair and think things impossible“.[Novum Organon, 1604]. But sometimes a man has the imagination, or effrontery, to see beyond his fellows, and so to build a marvel which they all thought impossible. Such a man was Lo Woltjer who built the VLT, now the most powerful optical telescope on Earth.

In 1976, during a conference in Italy I overheard him say over lunch ‘It’s time for Europe to take back the lead in Astronomy from America’. At the time I thought that idea preposterous but overnight I changed my mind and went to talk to him . I had spent spent several years analysing the Scaling Laws of telescopes, that is to say how their effectiveness and cost scale with their mirror diameter D. Naively I had imagined all would scale with the mirror area, that is to say with D2 , but that turned out to be very far from the truth. Big mirrors also collect unwanted sky light (noise) while some major costs could rise as fast as D4 . Why? Because if they are to focus the light, telescopes cannot afford to bend, and bending moments scale as D4 — that’s why big trees are so much stouter in proportion than saplings. And in engineering, costs tend to rise in proportion to weight. I had thus concluded (1972) that large telescopes were disproportionately expensive and should be replaced by arrays of smaller ones which could add their signals together.

When I went to talk to Lo he was sitting under a tree reading Tacitus’ “The Agricola and the Germania” because he was an historian at heart, son of an eminent Dutch historian. He took the long view, saw the big picture, and realised that America’s huge lead was a temporary consequence of finding better telescope sites in its own back yard. But the coming of the jet airliner Woltjer saw as a chance for Europe to catch up, indeed overtake America in mankind’s race to decipher the Cosmos. He asked me to spend 6 months at his European Southern Observatory (ESO) headquarters, then in Geneva, and help with his visionary plan — which I afterwards did.

In 1977 Woltjer organised a huge conference on Big Telescope Design in Geneva at the end of which he announced his vision of a 16-metre class European telescope at a time when the largest was the 6 metre Russian instrument. 21 years later his his vision bore fruit when the VLT (‘Very Large Telescope’) saw First Light high up in the Chilean Andes. This is now recognised to be the most powerful astronomical facility on Earth, generating even more research papers than the Hubble Space Telescope, which cost ten times as much.

vlt

The VLT up at La Paranal up in the Chilean Andes. It looks nothing like a conventional telescope because the mirror area is equally divided between 4 largely identical 8.2 metre units, each in its own rotating enclosure. The 4 smaller auxiliary telescopes in domes combine with the 4 monsters for the purposes of optical interferometry. Such a single image can convey little of the ingenuity going on inside. For that see later

I played only a minor roll in the VLT’s eventual evolution and confess I’ve never used it because my primary interests turned in other directions, such as Hidden Galaxies for which it wouldn’t be useful. But I would like to celebrate what seems to be a most extraordinary personal , as well as a European-wide, achievement. So many challenges had to be met, so many stubborn minds had to be persuaded, so many co-workers had to be inspired to realize a dream built out of glass, electronics and light. Whereas one can marvel at other great constructions like Stonehenge and Agia Sophia we know almost nothing of how they were built , or even who built them, but the VLT story is still acccessible , not least in Woltjer’s own modest book “Europe’s Quest for the Universe” [2005]. Fascinating episodes include:

Deciding on its fundamental configuration , which had to be a series of tricky trade-offs between performance, politics and cost.

Finding the very best site when cloudlessness and atmospheric steadiness do not necessarily go together.

Building huge mirrors which are very light, yet optically and thermally stable. Eventually the Schott company cast the 8.2 metre monoliths out of its proprietry Zerodur which took months and months to cool as they were spun into shape. Lo Woltjer’s chief optician, Ray Wilson from Brum, devised active support mechanisms which thereafter kept those mirrors in perfect shape as they were tilted to follow the sky. Not least was the challenge of moving such huge but fragile structures via the waterways of the world to their eventual home atop the Andes.

Any telescope’s performance can be ruined by turbulent air bubbling anywhere near it, hence its housing is vital. The VLT housings, while protecting the telescopes from wind and weather, leave them largely out in the pristine night air. This novel design was proof-tested on ESO’s smaller NTT and appears to work remarkably well.

The demands of near-infrared astronomy on a telescope are different from the optical variety. For instance the massive secondary mirrors have to be wobbled at 10 Hertz or more to subtract off the much brighter infra- red sky. At some considerable cost this was achieved by building them out of light but very tricky Beryllium.

Any telescope is only as good as the Instruments fitted to it to analyse and record its light. Here Woltjer took a leaf from Space Astronomy. Such Instrument’s specifications were sent out to tender across Europe, with the winning teams not only paid but rewarded with large grants of telescope time to do their own Science. This not only challenged the best of European brains but built up invaluable infrastructure across the continent.

Last, but not least, Woltjer and his chief lieutenant Maximo Tarenghi had to deal with a Chilean government which was traumatized by the brutal Pinochet coup. They had to sup with some real devilsL

Last but not least , Woltjer and his chief lieutenant Maximo Tarenghi had to deal with a Chilean government rocked by Pinochet’s very violent coup. At times that meant supping with some pretty vile devils.

But in the end, somehow everything came together and worked superbly, so that, in my opinion, the VLT is one of mankind’s greatest achievements, reminding us of what we humans, at our best, can do.

No blog or image can possibly do justice to Lo Woltjer and his great achievement but, as you might expect, ESO runs a quite wonderful website at eso.org and if you look there under ‘Movies’, or on You-Tube, you can find ‘VLT trailer’ , a stirring evocation of this magnificent project, fanfare and all.

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