A LunarLiquid Mirror Telescope (LLMT) is under study thanks to a grant from NASA. J.Roger Angel, a regents professor at the University of Arizona, is leading aproject to study the feasibility of a 100 meter LLMT at the moon's south pole.
Why liquid mirrors? Eversince 1668, when Isaac Newton built the first reflector telescope with aone-inch diameter mirror made of metal, astronomers have longed for biggerparabolic mirrors. Opticians expend a great deal of effort to grind larger andlarger pieces of glass to just this shape.
Liquid Mirror Telescopeswere first talked about several hundred years ago. Imagine a bowl of mercury atthe center of a lazy susan. When you give it a spin, the surface of the liquidforms that highly prized shape - a parabola. The bigger the bowl, the biggerthe resulting mirror.
The first serious attemptsto actually build a LMT took place in the early twentieth century. Robert W.Wood, a physicist at Johns Hopkins University, built a working telescope, butcould not accurately control the speed of the turntable, resulting in a mirrorwith a variable focal length. (The rotation must be controlled to less than onepart in 100,000 during exposure.) Pictures of star trails were focused in someplaces, but blurry in others.
The LMT concept has beenmade to work. The Large Zenith Telescope at the University of British Columbiauses a 6-meter mirror, making it the third largest optical telescope in NorthAmerica. It was built at a cost of approximately $1 million. A telescope with aconventional glass mirror of the same size would cost $100 million.
It is hoped that similarsavings might apply when constructing telescopes on the moon. In addition, themoon is completely free from atmospheric absorptions and distortion.
The only disadvantage ofthe LMT is that you cannot tilt it; it must remain perpendicular to the localgravitational field. You can only use it to look at what is directly above thetelescope; however, a mirror of this size could take a very penetrating look atits patch of sky.
"You would be seeing things farther back in time thananyone has ever seen any galaxy or star or quasar," [Angel] explained."It could give you a chance to see what was happening at a very earlytime."
(From J. Roger Angel and the LLMT)
Obviously, for such aproject to be attempted, there would need to be substantial infrastructurealready im place on the moon. As Dr. Angel remarked, "You could not justifythat kind of infrastructure (just) to build this kind of telescope, but if theinfrastructure already were there, this is something that looks feasible todo."
There is a very earlyreference to a large liquid mirror telescope in science fiction; but this LMTis on Mars, not the moon. In his excellent 1934 novella OldFaithful, author RaymondZ. Gallun writes about a Martian named 774, who has a desperate need tocontact Earth:
Piercing the dome, opposite the upper end of the cylinder,was a circular opening through which a portion of the starlit sky was visible;and at the base of the cylinder a great bowl rotated rapidly, like a hugewheel... The bowl contained mercury. As the container spun on its perfectlybalanced axis, centrifugal force caused the mercury to spread in a thin,precisely distributed layer over the inside of the bowl, forming a concavesurface that acted admirably as a mirror for Number 774's gigantic reflectingtelescope. It's area, and its consequent light-gathering capacity, was manytimes greater than any rigid mirror that could have been constructed withoutflaws.
(Gallun appears to err in his use of the LMT; read more about the Martian LMT)
(This Science Fiction inthe News story used with permission from Technovelgy.com - where science meets fiction.)