In the early 1900s, Henrietta Leavitt made one of the most important discoveries in the history of astronomy: a yardstick to measure distances to faraway stars. Using this tool, scientists eventually transformed our understanding of the universe. They realized space was expanding, that this expansion was accelerating, and that ultimately, everything will end. For more, go to http://vox.com/unexplainable It’s a great place to sign up for our newsletter, view show transcripts, and read more about the topics on our show. Also, email us! unexplainable@vox.com We read every email. Support Unexplainable by making a financial contribution to Vox! bit.ly/givepodcasts Learn more about your ad choices. Visit podcastchoices.com/adchoices