I've always been a big fan of astronomy. One reason is that I love being exposed to new, novel concepts, and the universe is big enough that we are continually coming across new things we've never seen before and don't know how to explain. One such example is V838 Monocerotis, a star in our own galaxy. Three years ago, it suddenly became the brightest star in the Milky Way, and then quickly faded again. While it's certainly perplexing trying to figure out what caused its strange behavior, the part I find cool is the interesting image of the star captured by the Hubble telescope. The wispy nebula-looking structure surrounding the star is actually an echo of the expanding sphere of light emitted by the star when it performed its burst — some of the light bounces off interstellar dust and is reflected in our direction, so we effectively get to witness the speed of light. This is most dramatically visualized in this animation produced by the European Space Agency, morphing between five successive images taken over the course of a year and a half.

At first I wondered how it was possible — since light is the fastest known thing in the universe, there's no way to "see" a sphere of light expanding off in space, because you wouldn't see it until the sphere had reached you. But the key is in the fact that it is light reflected off of dust; it didn't travel in a straight line to get to us. The light that was aimed directly at us reached us first, and was what made the star appear so bright. The light that was emitted in other directions and was then reflected towards us had a longer path to travel, which explains why it took several more months to reach us. Very cool.