A liquid mirror telescope is made by spinning a reflective fluid, such as mercury, at a constant rate. This rotation produces a parabolic surface, which is an ideal shape for a telescope mirror. (You can try this yourself.) While these mirrors can be built to be large and orders of magnitude cheaper than solid mirrors, they have the disadvantage that they can only look straight up. Creating mirrors this way is not new; they have a history [.ps] that dates back to Newton. However, they have recently regained attention as the technology behind proposals to build an enormous (20m+) telescope on the moon. (A less technical treatment here.)
posted by Upton O'Good on Jul 1, 2008 - 36 comments