Magellan Telescopes

The 6.5-meter Baade and Clay telescopes were built by the Carnegie Institution of Washington at 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 Walter Baade Telescope was the first of the twin 6.5 meter Magellan telescopes to be completed in 2000, followed by the Landon T. Clay telescope, finished in 2002. The two telescopes are located 60 meters apart on an isolated peak (Cerro Manqui) at the Las Campanas Observatory. The telescopes are an alt-azimuth design. The principal foci are f/11 at the two Nasmyth locations and f/15 in the Cassegrain position, although at present only the f/11 focus is implemented on the Baade Telescope. In addition, three auxiliary f/11 are provided on the center section. An ADC corrector will be available for f/11 use to provide unvignetted fields up to 24 arcmin. Platforms on either side provide access to the instruments at the principal Nasmyth ports.


The Magellan primary mirrors were cast and polished by the Steward Observatory Mirror Lab. They 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 performs 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).

Telescope and dome

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 telescope and enclosure are designed to minimize image degradation due to thermal effects. Separate ventilation systems for the enclosure, telescope structure, and primary mirror maintain surfaces within the dome at the outside air temperature during night time observing.

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.

Active Optics
Active controls are incorporated in the telescope optics. The mirrors have position control for alignment. These are active during observing. Figure control of the primary mirror is used to correct low-order aberrations in the optical system. In addition, the secondary mirror has a tip-tilt mechanism for fast guiding.