Star Points for March 2009 by Curtis Roelle California's Mt. Palomar Observatory The 200-inch Hale telescope on Mt. Palomar, in California's Cleveland National Forest, is a massive piece of engineering. Built in 1948, the Hale was the largest telescope in the world throughout the 1950s, 60s, and much of the 70s. It is one of the high temples of astronomy. I have always wanted to make a pilgrimage to this fascinating place, and this year it finally happened. Some expiring frequent flier miles were the incentive for my making an impulsive decision to visit warm San Diego in January. On the morning of departure the temperature here was +1 degree Fahrenheit. When I arrived in San Diego, the evening temperature was some 70 degrees warmer. The observatory can be reached in less than two hours by car from San Diego. The road winds through some picturesque land filled with colorful orchards, mountains, and Native American gambling casinos. The ground at the top of 5,500-foot Mt. Palomar was covered in snow under a sunny blue sky. Prior to the Hale, the largest telescope in the world was the Hooker 100-inch telescope, another California-based instrument located on Mt. Wilson near Pasadena. With a mirror diameter twice that of the Hooker, giving it four times the light gathering power, the Hale telescope was a giant leap in aperture size. Construction began in 1936 for the observatory's domed building. The parts for the telescope were built in different parts of the country and shipped to the mountain for assembly. The 200-inch mirror blank was poured at the Corning Glass Works in New York. The first blank cracked during the cooling phase. It is currently on display at the Corning Museum of Glass in Corning, New York. The second glass blank weighed 20 tons and required nearly 11 months to cool down from its initial molten state at a temperature of 2,700 degrees Fahrenheit. In 1936 the blank was shipped to California for grinding, figuring, and polishing. World War II intervened, so the mirror was not completed for nearly 12 years. The telescope opened for regular operations in 1949. Once inside the observatory, guests climb a curving staircase to reach an observing gallery overlooking the observatory floor. The cavernous dome arches 90 feet above the floor, and sitting in the middle of the floor is the venerable behemoth, the Hale itself. Its mounting consists of two massive supports at the north and south ends of the polar axis. The telescope tube is built using an open truss. I was lucky to get a private tour out on the observing floor itself. Standing beneath the telescope and looking up through the tube at the secondary mirror at the far end high overhead was an almost overwhelming experience. The five-meter-diameter telescope was eclipsed in 1976 by a six-meter telescope at a Russian observatory in the Caucasus Mountains, and that one in turn has been surpassed by ever larger ones. In the 400 years since Galileo first looked at the sky with his telescope in 1609, his invention keeps improving and getting larger. In the past several months I've been fortunate to have visited two California telescopes that were once the largest in the world: in August, the 36-inch Lick near San Jose, the largest in the world from 1880 to 1888; and in January, the 200-inch Hale near San Diego, the largest telescope from 1949 to 1975. Nowadays, telescopes are being placed higher and higher: not only on tall mountain peaks, but also launched into space to orbit high above the world and its obscuring blanket of atmosphere. But even the Hubble Space Telescope, the most famous of them all, has less than one fourth of the light gathering ability of the venerable Hale telescope.