TEL20 Steward Observatory 12meter millimeterwave telescope

The radio telescope housed inside a fabric dome on the Southwest Ridge has a diameter of 12 meters; its first observations were ^ done in 1968, though with a smaller (36-foot) antenna. Until the summer of 2000, it was operated by NRAO; control then passed to Steward Observatory, which operates it together with the Submillimeter- — wave Telescope Observatory on Mount Graham (about 70 miles northeast of Tucson, in the

Pinaleno Mountains). The 12-meter antenna of Steward Observatory can Both telescopes use be seen inside the rubberized fabric dome. The the same basic tech- dome rotates with the antenna. Photo by L.J.S.

nology, so that equipment can be used on both.

The dome rotates with the telescope, sheltering it from the Sun and wind; it operates 24 hours per day, unlike the optical telescopes. It also can observe at some wavelengths through light cloud or fog. The main bearing of the telescope - on the azimuth axis, which bears the entire moving weight - comes from the mount of a 1960s vintage army tank. The telescope was closed for almost a year in the early 1980s, for installation of its present antenna, which is larger and has a smoother surface than the original one.

This is the telescope where "light" from carbon monoxide (CO) molecules in the Orion Nebula was first detected in 1970. Carbon monoxide turns out to be the most abundant molecule in the Universe after molecular hydrogen (H2). This discovery launched the field of molecular astronomy, which has revolutionized our understanding of how stars form. Until the early 1970s the star-formation process was a mystery. Astronomers could see lots of atomic hydrogen in our Galaxy, but it did not exist in dense enough clouds to collapse into stars. Yet they could see many bright young stars, particularly in locations like the Orion Nebula (M42), posing a considerable problem. It turned out that once the atomic hydrogen got cold enough and dense enough, it all went into molecular form - two hydrogen atoms joined together to make a hydrogen molecule. This molecular hydrogen protected other molecules from being shaken apart by energetic light from massive stars, and those other molecules - particularly CO - acted as "coolants" for the hydrogen. Because the CO was getting rid of the energy, the molecular hydrogen could get very cold and dense, allowing stars to form.

The 12-meter telescope has also been instrumental in establishing just what other molecules are out in space, which has allowed chemists to build computer models of the chemistry of molecular clouds. This work provided the basis on which has been built the beginnings of astrobiology, one of whose goals is to establish where the building blocks of life might be made, and therefore where life might be possible.

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