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

Reversible flow! In the 1960s, the National Committee for Fluid Mechanics Films produced a series of films for education in fluid mechanics. This clip is part of "Low Reynolds Number Flow"; you can find the entire collection streamed here. Interesting demonstrations abound. (1st link is QT; rest are RealPlayer.)
posted by Upton O'Good on Aug 17, 2007 - 19 comments