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Where 20th century astronomers mastered the skies (pictures)

For nearly 50 years, Palomar Observatory's Hale Telescope, near San Diego, was the most important device of its kind in the world. Even now, it's still used 290 nights a year. CNET Road Trip 2012 stopped by to check it out.

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Daniel Terdiman
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Star trails

PALOMAR MOUNTAIN, Calif.--For much of the 20th century, the Hale Telescope, at the Palomar Observatory, in the mountains northeast of San Diego, was the best place in the world to study the skies.

With its groundbreaking 200-inch telescope, the Observatory -- which is owned and operated by the California Institute of Technology -- allowed scientists to discover radio galaxies, quasars, and more. But the site is home to several other important telescopes that have also been instrumental in astronomy.

As part of Road Trip 2012, CNET reporter Daniel Terdiman stopped by the observatory for a close-up look at one of America's most important scientific sites.

Here, we see time-lapse photography of the 200-inch dome and the trails of hundreds of stars in the sky.

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200-inch telescope

A look at the 200-inch Hale Telescope, inside the Palomar Observatory's main dome. The telescope was first put into service in 1948, and until 1993, it was the world's largest effective telescope. Even today, however, it is still used by scientists nearly 300 nights a year.

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Underneath mirror cradle

A look up at the bottom of the cradle of Hale Telescope's 200-inch mirror. The mirror is designed to respond well to changing temperatures and weighs 14.5 tons with its steel cradle, or holding cell.

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Laser to the sky

According to the Palomar Observatory's Web site, "By projecting a laser into the sky, astronomers can create an artificial laser-guide star for use in adaptive optics wherever they see fit. To do so, they shine a narrow sodium laser beam up through the atmosphere. At an altitude of about 60 miles, the laser beam makes a small amount of sodium gas glow. The reflected glow from the glowing gas serves as the artificial guide star for the adaptive-optics system. The laser beam is too faint to be seen except by observers very close to the telescope, and the guide star it creates is even fainter. It can't be seen with the unaided eye, yet it is bright enough to allow astronomers to make their adaptive-optics corrections."

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Horseshoe

This is the giant "horseshoe" mount, or equatorial mount, that is used to allow the telescope to scan the entire sky, something that was essential to George Hale, the observatory's creator, who had failed at such a goal with his previous telescopes in Wisconsin and in Los Angeles.

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Two yokes

A look at the top half of the Hale Telescope from a walkway erected above the floor in the 200-inch telescope's dome at the Palomar Observatory. In the photograph, it is possible to see the large holes of both of its yoke arms. The one on the right contains a spectrograph, while the one on the left has the telescope's motors and gearing.

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Polishing the mirror

It took from 1936 to 1947 to grind the 200-inch mirror. According to the Palomar Observatory Web site, "In the optics lab at Caltech, the front surface of the mirror is ground to the approximate concave form required. Using successively finer polishing grit, the opticians then carefully smooth the surface, constantly using optical tests to compare it to a perfect paraboloid shape. It is slow and painstaking work. To make the final mirror, almost 10,000 pounds of glass are polished away, including the top two inches which contain 'scar tissue' left over from the casting and annealing process."

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Elevation bearing

The circle in the middle left of this photograph that appears to have spokes like a bicycle wheel is one of the telescope's two elevation bearings, which are used in the process of raising or lowering the telescope.

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Dome doors from the inside

Taken during the day, this photograph shows the 200-inch telescope's giant cover doors while they are closed.

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200-inch dome

A look at the outside of the 200-inch telescope dome at Palomar Observatory.

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West arm

This is the telescope's west arm, which has the giant device's gears and motors installed inside.

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Drive system east-west

This is the drive system that allows the Hale Telescope to move on an east to west axis.

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Plumbing for oil pads

Rather than using mechanical bearings to support the 520-tons of moving mass that is the Hale Telescope, it relies on oil bearings. It amounts to a ball and socket joint on the south side of the telescope that floats the entire assembly. This is the plumbing that routes the oil up into the bearing.

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Cradle

A look at the Hale Telescope's 200-inch mirror cradle.

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200-inch dome 2

Another look at the 200-inch telescope's giant dome, at the top of Palomar Mountain.

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Data room

Although astronomers are the scientists doing experiments and research at the Palomar Observatory, they are not allowed to do the actual controlling of the telescope. That job falls to a telescope operator, who sits at this station in the "data room."

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Close-up controls

A close-up look at the controls in the telescope's data room.

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Cement blank

This giant cement block is the same size, weight, and mass of the Hale Telescope's primary mirror and the holding cell that supports it.

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48-inch telescope

Palomar Observatory has other important telescopes, as well, including this one, the 48-inch telescope, which was used for several rounds of the Palomar Optical Sky Survey from the late 1950s until the early 1990s.

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18-inch dome

Another important part of the Palomar Observatory is the 18-inch telescope, which was used to discover supernovas.

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