Witness the first images of the September 2025 partial solar eclipse.
For over a century, scientists have known that the Universe is rapidly expanding. This phenomenon, named in honor of the astronomers who independently confirmed it (Edwin Hubble and Georges Lemaître), is known as the Hubble-Lemaitre Constant (or the Cosmological Constant). By the 1990s, the Hubble Space Telescope (designed to measure this constant) revealed that the rate at which the Universe was expanding was slower during the early Universe, which was in "tension" with measurements of recent cosmic epochs. This is what led to the "Hubble Tension" in astrophysics and cosmology, and the theory of Dark Energy (DE) as a possible means of explaining the discrepancy.
