I ♥ Cardioids, Vi Hart's condensed awesome tackles parabolas, cardioids, circles and more. Related: Part 1 of Rolling Circles and Balls.
"Pynchon, postmodern author, is commonly said to have a non-linear narrative style. No one seems to have taken seriously the possibility, to be explored in this essay, that his narrative style might in fact be quadratic." Number theorist Michael Harris on Pynchon and conic sections.
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.)