The Magellan Telescopes
Background
Large telescopes are custom-built and rare. There is no standard practice or model. Every time a large telescope is built, its designers must re-think the challenges, check every application, and improve on what has been done before.
The 6.5-meter Baade and Clay telescopes were built by the Carnegie Institution of Washington at its Las Campanas Observatory in Chile on behalf of the Magellan Project, a collaborative effort by the Carnegie Institution, University of Arizona, Harvard University, University of Michigan, and Massachusetts Institute of Technology. The Magellan Consortium consists of more than 200 senior astronomers, 100 postdoctoral astronomers, and nearly 100 Ph.D. students. Each partner has its own scientific agenda for the telescopes and assigns its share of telescope usage.
The Magellan main mirrors are f/1.25 paraboloids and a radical departure from the nearly solid-glass mirrors of the past. Each is 21,000 pounds of borosilicate glass with a lightweight honeycomb structure inside. It took 6 months to build the mold for each mirror, 2 days to fill it with chunks of glass, 1 week to melt the glass and spin it into shape (in a specially designed rotating oven), and 3 months for the glass to cool. Each was then polished for 8 months while its surface was constantly tested for accuracy. Relative to their size, the main mirrors are about as thin as a dime.
The aluminum surface of each mirror is a mere four-millionths of an inch (0.1 micron) thick. Each also sits in a "cell" that peforms two important functions. First, the cell's thermal control systems prevent warping from thermal expansion and contraction. Second, the support systems in the cells maintain the mirrors in their proper shape, so there is no distortion or cracking. The actual shape of the mirror surface is controlled to within two-millionths of an inch (0.05 microns).
The telescopes float on a film of high-pressure oil on a 9-meter diameter circular track. To prevent slippage, the drive cylinders and drive surfaces are forced together with 10,000 pounds of pressure. Astronomical images are tracked to within 0.02 arcsecond in calm conditions. The telescopes themselves are so well-balanced and frictionless that a gentle push from a child can move all their 150 tons.
The Magellan telescopes were designed with instrumentation as a foremost consideration. Astronomers use instruments, such as high-end CCD cameras and spectrographs, to record and analyze incoming light. The instrument platforms at Magellan permit rapid switching between different optical configurations in order to take advantage of changing weather, seeing, or moonlight conditions.
Results
The Magellan telescopes began operations in the early part of this decade and have already contributed new data and insights to a wide range of topics in astronomy, cosmology, and astrophysics. The First Symposium on Magellan Science (2005) and the Second Magellan Science Symposium (2007) highlighted the excellent performance of the telescopes and just some of the exciting research being conducted on them.
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