A University of Arizona-led team of astronomers has discovered that Type Ia Supernovae, which have been considered so uniform that cosmologists have used them as cosmic "beacons" to measure the depths of the universe, are not so constant after all. This discovery casts new light on the currently accepted view that the universe is expanding at a faster and faster rate, pulled apart by a poorly understood force called Dark Energy. The results have implications for big cosmological questions, including the possibility that the acceleration of the expanding universe may not be quite as fast as today's textbooks say.