 After Hubble discovered the universe was expanding, it was assumed that it started off with a tremendous expansion rate, and because of the gravitational attraction of all the matter in the universe, the expansion would be slowing down. Two major efforts were started in the late 1990s to prove that the universe's expansion was decelerating. Both groups used distant Type 1A supernova as their standard candles. Supernova provide a luminosity reading that enables us to determine their distance via the inverse square law. This distance is called the luminosity distance. Type 1A supernova also provide a redshift reading that gives us the distance by a Hubble's law. The intensity and redshift combined can tell us if the universe's expansion rate is constant, decelerating, or accelerating. Here's how it works. First, we measure the luminosity of a distant Type 1A supernova, like SN 1994D, and measure its redshift. Then we map the distance between us and the supernova over time. If the expansion rate is constant, the luminosity distance and the redshift distance will be the same. But if the expansion is slowing down, the expansion rate in the past would have been greater than what we see now, which means it would have taken a shorter time to expand from its size at light emission time to its present distance compared to a non-accelerating universe. This would result in a shorter light traveled time, shorter distance traveled, and a brighter observed supernova compared to a non-accelerating universe. By the same token, if the expansion is speeding up, the expansion rate in the past would have been smaller than what we see now, which means it would have taken a longer time to expand from its size at light emission time to its present distance compared to a non-accelerating universe. This would result in a longer light travel time, larger distance traveled, and a dimmer observed supernova compared to a non-accelerating universe. This is what both studies found. The universe is expanding, and the expansion is accelerating.