Telescope uses liquid mercury mirrors

LAVAL, Quebec, Oct. 12 (UPI) -- Telescopes that collect cosmic light using giant mirrors made of liquid mercury are a promising technology may significantly lower the high cost of making scientific discoveries in far off galaxies.

"Liquid mirror telescopes are of interest to astronomy because of their very low production and operating costs," astronomy professor Ermanno Borra, of Quebec's Universite Laval, told United Press International. "Low cost could have a potentially revolutionary impact on cosmological observation."

Mirrors in so-called "reflector telescopes" are used to focus light from distant objects.

"The mirror can be thought of as a big bucket that concentrates the light from a distant star in one point," Borra told UPI.

Glass mirrors, however, "are people intensive to make," said University of California-Los Angeles astronomer Ralph Wuerker from the HIPAS observatory in Fairbanks, Alaska. "It can take months or years of grinding to polish the surface and coat it."

"A glass mirror must also be periodically cleaned, aluminized and adjusted, a cumbersome, time-consuming process," Borra said. "By comparison, maintenance of a liquid mirror is virtually nonexistent."

"The bottom line -- a small university can have dedicated access to a large liquid mirror telescope for $10,000 to $20,000 as opposed to $10 million to $20 million or more for a similar-sized glass telescope," Robert Sica, associate professor of physics and astronomy at the University of Western Ontario, told UPI from London, Ontario.

The Italian astronomer Ernesto Capocci made the first known mention of a liquid mirror in 1850, making use of an earlier discovery that the surface of a spinning liquid takes the shape of a parabola -- the precise shape required for the mirror of a telescope.

In the early 20th century, the American physicist R. W. Wood built one of the first liquid mirror telescopes to observe the moon. Using a spinning dish with a 1-centimeter layer of mercury, Wood noted the mercury layer was too thick, slightly distorting the images. With the United States' entry into World War I, the Army commissioned Wood and assigned him to Paris, leaving unsolved the problem of a functional liquid mirror until Ermanno Borra approached it over seven decades later.

Contemporary liquid mirrors, Borra told UPI, are made of a much thinner 1-millimeter layer of mercury, placed on top of a parabolic, rotating container. Gravity pulls down on the liquid and centrifugal forces, which arise as the container spins, pull the mercury sideways.

"Gravity remains constant but the centrifugal force increases outward as the speed of rotation increases," Borra said. "This forces the surface of the liquid to take a parabolic shape, which is ideal for an astronomical telescope."

Borra's approach to liquid mirrors has satisfied astronomers worldwide.

"Today's liquid mirror telescopes are low cost, wonderful instruments for astronomical surveys," said astronomer Jean Surdej, of the Institute for Astrophysics and Geophysics at the Universite de Liege in Belgium. "Another benefit -- they cannot be damaged."

"Our liquid mirror telescope is 2.7 meters -- 100 inches -- in diameter," Wuerker told UPI. "It is six years old and has turned out to be very reliable and trouble free. A polished glass telescope of its size would have cost 10 to 20 times more."

Mother nature herself can take credit for the success of liquid mirror technology and the failure of traditional glass mirrors, Borra explained.

"Liquid mirror telescopes are cost effective because the basic laws of nature -- gravity and centrifugal force -- conspire to give them the right shapes," Borra said. "This is unlike glass that must be polished and kept in an expensive mount. The basic laws of nature -- gravity and heat -- conspire to destroy the shapes of glass mirrors."

(Reported by Mike Martin in Columbia, MO.)