How Do We Know How Far Away the Stars Are?

Nobody has ever travelled to another star. So how do astronomers know how far away the stars are? In under six minutes, join Ari the robot and measure the universe with nothing but angles and light. Try the thumb trick that reveals parallax, borrow Earth's orbit as a giant measuring baseline, turn a tiny sideways shift into a distance, then follow Henrietta Leavitt's pulsating stars all the way to other galaxies. CHAPTERS 00:00 How far is that star? 00:28 Try it with your thumb 00:48 Measuring across a river 01:01 Borrowing Earth's orbit 01:35 Parallax: the tiny shift 01:49 Turning an angle into distance 02:28 Light-years and parsecs 02:40 Our nearest stellar neighbour 02:51 The Gaia spacecraft 03:21 When parallax runs out 03:36 The streetlight experiment 04:08 Henrietta Leavitt's Cepheids 04:35 Climbing the distance ladder 05:04 What could fool us 05:18 A sky with depth "Ari and the Star Ruler" is an original ARK educational animation with synthetic narration. Illustrations are simplified; sizes, angles and motion are exaggerated so you can see them. Real stellar parallax angles are far smaller than shown. Sources: ESA — Gaia and cosmic distances · ESA — How Gaia studies the Milky Way · NASA — Henrietta Leavitt and Cepheids · NASA — Hubble and Gaia calibrate Cepheids Which clue surprised you most: the thumb trick, the streetlights or the pulsating stars? Tell us in the comments, and subscribe for more animated science. #Astronomy #Space #ScienceExplained