How is an exploding star like a tape measure? That’s not a riddle! Astronomers use a type of supernova, called type Ia, to measure distances to faraway galaxies. These supernovae come from the collapse of a type of dead star called a white dwarf. Since they are all triggered by similar events, we know approximately how much light they emit. Using that, and how bright they appear to be, we can tell how far away these supernovae were. It’s like having a giant ruler. #NationalTapeMeasureDay | NASA