Hubble and Gaia (image) NASA/Goddard Space Flight Center Share Print E-Mail Caption Using two of the world's most powerful space telescopes -- NASA's Hubble 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 as measured by Hubble, with their apparent brightness as seen from Earth, scientists can calculate their distances. Gaia further refines this yardstick by geometrically measuring the distances to Cepheid variables within our Milky Way galaxy. This allowed astronomers to more precisely calibrate the distances to Cepheids that are seen in outside galaxies. Credit NASA, ESA, and A. Feild (STScI) Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.