February General Meeting
Speaker Professor Warrick Couch
from Swinburne University of Technology, on the subject:
The Next Generation of Very Large Telescopes.
This time of the year you have to come real early to ASV meetings if you want to catch a parking spot in the Kings Domain. The line of parked cars stretched uninterrupted from Alexandra Avenue to Domain Road. We just made it into the Observatory Ground parking area before the Shakespearean Players closed that access too, to begin their Mid-Summer Night performances.
Large and extra large telescopes make the news often enough for an astronomy minded public to be reasonably informed. On top of that these projects cast a long shadow, they extend over decades and nothing much seems to happen in a hurry for years. So it is interesting to note that the Herbarium Hall did fill up to capacity (albeit slowly due to the parking problem mentioned above). But then, Warrick Couch is a high profile scientist, a Citation Laureate, which means he ranks amongst the most often cited scientists in Australia. His principal interest lies in extra-galactic astronomy and cosmology and his research involves major observational programs using the largest ground-based optical telescopes as well as the Hubble and Chandra space facilities.
The talk centred on the need of, and the justification for Extra Large ground based Telescopes. For a long time it was thought ground-based optical telescopes were limited in their resolution not only by the diffraction limits of the telescope but also by the “Seeing” condition imposed by the surrounding air. While an increase in size would improve the diffraction resolution, nothing seemed to be able to be done about air turbulence in the line of sight of the telescope. That is, any extra light gathering potential of a larger telescope would be offset by an inevitable loss of definition; until Adaptive Optics came on the scene. Warrick demonstrated on hand of a short schematic video how any lateral changes in the image of a known point source (either a star or a Laser beam) sensed electronically, can now be instantly compensated for by appropriate deformation of either the main or the secondary mirror, thus keeping the image in focus. The system has been perfected to such a degree that full advantage can now be made of the large mirrors’ light collecting potential and their lower diffraction limits. It is anticipated the new generation of Extra Large Telescopes will excel the image quality so far only possible with the Hubble or the Chandra Space telescopes.
The investments are huge. The Giant Magellan Telescope (GMT – a combined Universities project) with a 25 metre diameter, seven segment mirror and adaptive optics, scheduled for completion in 2017 has an estimated cost of U$580,000,000. Other projects of this type in the pipeline are the Extra Large Telescope (ELT – Canada/USA) with a diameter of 30m, priced at U$1Billion, and the tentative OverWhelmingly Large Telescope (OWL – a European Communities proposal) with a 100m mirror diameter. Professor Couch related a humorous anecdote concerning the latter, that is, due to “overwhelming” difficulties with the design of the gigantic OWL dimensions, the telescope may shrink somewhat before construction begins and, rumour has it, the acronym OWL actually stands for a telescope that “Once Was Large”.
Many questions followed the end of the talk, and Warrick Cough showed himself equally at home on telescope design and on cosmology. Ken Beard gave the vote of thanks to general acclaim.