|Our understanding of the Universe and the technology used to observe it is constantly evolving. When Edwin Hubble discovered that the Universe was expanding in 1929 with galaxies becoming increasingly distant from one another, scientists reasoned that the gravitational attraction between galaxies would slow the expansion rate of the Universe. But then in 1998 two teams of scientists discovered that the expansion rate of the universe was not in fact slowing down but that it was actually accelerating. This discovery created one of the largest cosmological conundrums of our day: what is causing the Universe to accelerate? This science bulletin travels to Lick Observatory and Fermilab, where scientists are working to untangle the mystery of cosmic acceleration. From the American Museum of Natural History.