Science |
Liquid Telescope For The Moon
A new project has come along that will allow us to have a giant telescope on the moon. We are seeing huge telescopes being constructed on the Earth that contain large mirrors and sometimes multiple large mirrors. A telescope that uses a mirror for its main lens is called a reflecting telescope. There was a time when refracting telescopes were getting bigger and bigger, but they became unwieldy since they required precisely ground lenses at the front of a long tube. Since the light enters one end of the tube, it has to travel all the way down the tube to the eyepiece which is another series of lenses. The biggest refracting telescope ever constructed has a 40 inch lens and is located at the Yerkes observatory. The 40 inch telescope, with its massive mount, was actually set up at the Columbian Exposition in Chicago in 1893, so that the public could see it. A reflecting telescope comes in many different flavors. All have a somewhat folded light path so the tubes can be shorter than those of a refractor and since the heaviest part is at the bottom, the mirror, they are easier to handle. The most common type of reflecting telescope features an eyepiece that is set into a tube on the side. At one end of the tube is the mirror, it is at the opposite side from the eyepiece which is on the side but near the top. On the other end of the tube a small diagonal mirror is mounted, but it is mounted in such a way that most of the tube is open on that end. This allows light to go down the tube, hit the mirror which focuses it into a narrow beam and sends it to the diagonal mirror and up the eyepiece.
Reflecting Telescope Almost all astronomical optical telescopes being built today are reflecting telescopes, except for the small ones sometimes used by amateur astronomers. The ones in observatories all used to be mounted on extremely heavy mounts knows as equatorial mounts. This allowed the scopes to follow an object using a mechanical drive. A cheaper and lighter mounts is known as the alt alt azimuth mount. It can only move in azimuth and elevation. This type of mount used to be out of the question for observatories, since it was not precise enough and needed too many ongoing corrections to follow an object. This all changed when computers came into common use. They had the ability to make thousands or even millions of corrections a second as required, thus the cheaper and lighter mount became viable. The reflecting telescope that is being proposed for astronomy from the moon, would have a mirror that is as big as a football field. This would be the biggest mirror ever used in a telescope and bigger than the multi mirrored telescopes. How can a mirror of this size ever be manufactured? That is easy, it won't be. Instead what is being proposed is a coating of silver on a dish of ionic liquid. They are actually going to pour a liquid into a giant bowl shaped indention and then put silver over it. This will give the liquid a very smooth surface and be able to function even on the cold surface of the moon. The mirror will function as a mirror for a giant reflecting telescope and allow us to see wonders in the universe that we were never able to see before. Not only will the moon provide a stable platform for this telescope, but since there is no atmosphere the seeing conditions will be perfect. To realize what we are talking about, lets look at the Keck telescopes. We are talking about two optical telescopes that each have 400 inch mirrors and can be used together in a system called interferometry. That is where the light from more than one instrument is fed to a single source, thus increasing the light reaching the viewer. It is almost as good as having a much larger mirror, but two 400 inch mirrors don't give you an 800 inch view. Now lets look at the size of the mirror that is being considered for the moon. It will be about 100 yards in diameter, that is 3600 inches. Keck is 400 inches so this mirror will be 9 times bigger. The light gathering ability of a mirror is calculated by multiplying its diameter against itself, thus Keck's number is 160,000 but the moon telescope is 12,960,000. That means that the moon mirror will gather 81 times as much light. This doesn't take into account that the liquid might not be as reflective and this would lower the number, if that turns out to be the case.
Hubble Space Telescope So how would this mirror work? One method is to spin the liquid. Spinning it causes it to form a concave surface which would focus light. The scientists pushing this project say that they have found a more reflective liquid. to use than the mercury mirrors used on Earth, thus creating greater reflectivity. Detractors and there are many, say that the plan has basic problems and one main one is, that dust from the moon will settle on the liquid. mirror, decreasing its usefulness. They also say that the mirror would have to remain pointing in one direction. They prefer telescopes in space. Can these obstacles be overcome and can the moon scope ever become functional? The moon telescope is decades away, in that time period who knows what new discoveries might make it more viable. Some method might be found to respell dust and while not moving the mirror, they still might be able to aim it at different areas even behind the moon. Perhaps this could be accomplished with a system of satellites that would deflect the view?
Proposed James Webb Space Telescope. It is about 3 X the size of Hubble I imagine that with a telescope of this size, views of planets outside the solar system would become common place. I know that I would love to see such a scope being built, how about you? |
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