Views: 522273 | Rating: 4.95 | Likes: 9790

Distances: Crash Course Astronomy #25

How do astronomers make sense out of the vastness of space? How do they study things so far away? Today Phil talks about distances, going back to early astronomy. Ancient Greeks were able to find the size of the Earth, and from that the distance to and the sizes of the Moon and Sun. Once the Earth/Sun distance was found, parallax was used to find the distance to nearby stars, and that was bootstrapped using brightness to determine the distances to much farther stars.

Table of Contents
Ancient Greeks Finding the Size of the Earth 1:07
Earth/Sun Distance Began Our Use of Parallax 5:39
Brightness Relation to Distance 9:07

PBS Digital Studios:

Follow Phil on Twitter:

Want to find Crash Course elsewhere on the internet?
Facebook –
Twitter –
Tumblr –
Support CrashCourse on Patreon:

PHOTOS/VIDEOS
Lunar Ecplise [credit: Phil Plait]
Venus & Mercury [credit: Phil Plait]
Venus Transit [credit: NASA]
Black Drop Venus Transit [credit: Wikimedia Commons, H. Raab, Johannes-Kepler-Observatory]
New Horizons Approaching Pluto and Charon [credit: NASA/JHU APL/SwRI/Steve Gribben]
Radio Telescopes Diagram [credit: Alexandra Angelich, NRAO/AUI/NSF]
61 Cygni [credit: Caltech / National Geographic Society / STScI]
Proxima Centauri [credit: ESA/Hubble & NASA]
Dying Star [credit: NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA)]
Exploding Star [credit: NASA, ESA, J. Hester, A. Loll (ASU)]
Animation of a Variable Star [credit: NASA, ESA, M. Kornmesser]
Hubble’s High-Definition Panoramic View of the Andromeda Galaxy [credit: NASA, ESA, J. Dalcanton, B.F. Williams, and L.C. Johnson (University of Washington), the PHAT team, and R. Gendler]