Hubble and Gaia measure Cepheid variable stars

Using two of the world’s most powerful space telescopes — the NASA/ESA Hubble Space Telescope and ESA’s Gaia — astronomers have made the most precise measurements to date of the Universe’s expansion rate. This is calculated by gauging the distances between nearby galaxies using special types of stars called Cepheid variables as cosmic yardsticks. By comparing their intrinsic brightness — measured with Hubble — with their apparent brightness as seen from Earth, scientists can calculate their distances. Gaia further refines this yardstick by measuring the distances to Cepheid variables within our Milky Way Galaxy using astrometry. This allowed astronomers to more precisely calibrate the distances to Cepheids that are seen in other galaxies.