Light: Crash Course Astronomy #24

Share it with your friends Like

Thanks! Share it with your friends!


In order to understand how we study the universe, we need to talk a little bit about light. Light is a form of energy. Its wavelength tells us its energy and color. Spectroscopy allows us to analyze those colors and determine an object’s temperature, density, spin, motion, and chemical composition.

Crash Course Chemistry posters are available at

Table of Contents
Light is a Form of Energy 0:39
Wavelength Tells Us Its Energy and Color 0:59
Spectroscopy 7:28

PBS Digital Studios:

Follow Phil on Twitter:

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

Wavelengths [credit: Imagine the Universe! / NASA]
Observatories across spectrum [credit: Imagine the Universe! / NASA]
Red hot spiral hotplate [credit:]
The Crab Nebula [credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)]
Building the Space Telescope Imaging Spectograph [credit: NASA]
VST images the Lagoon Nebula [credit: ESO/VPHAS+ team]
Jupiter [credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute]
Venus [credit: NASA – NSSDC Photo Gallery Venus]
Ring Around SN 1987a, image 1 [credit: Jason Pun (NOAO) and SINS Collaboration]
Ring Around SN 1987a, image 2 [credit: George Sonneborn (GSFC) and NASA/ESA]


camavita says:

This ten-minute video made me understand atomic structure where two semesters of chemistry failed. Thank you, Crash Course! Love what you do!

HakingMC says:

"Purple is bluer than blue." Umm… Sure!

Nerdy says:

I'm a big fan of CrashCourse! I have a request. Can you please do a video about northern lights?

Kilo Mintoni says:

Light Wave Particle Duality. Behaves as a wave and yet is a particle..wut???? A photon?Basic Chemistry. Your thing is Fun for a four year old. You should probably lay off the antidepressants! Basic Physics. Hey, develope and explain your sun screen product that protects you from the Gamma rays constantly passing through you everyday. Clouds or not. HA! Go read some Tesla. HA!

Ranit Das says:

love the videos….

Vinod Kumar Gupta says:

I luv u guys so much…thnxx for making my life easier

Democritus86 says:

anyone else that could tell the difference in the squares? its seemed the right was a bit more metalic and shiny than the left one that was looking more matt.

amir shantia says:

Hey when will you guys create a Physics playlist?

Brian Holden says:

Um what? If light is a collective word for photon, which is a particle, and if wave is a particle effect then light is not a wave, the cause of wave patterns is particle physics.

coc0s says:

Those red squares are the same color. I checked the numbers for them in Photoshop.

Piffrock says:

Question : How do we know some light we see is redshifted ? How are we sure that the object we're looking at doesn't stay at the same distance, but its atoms emit the light the way we see it ?
Is it because the more you watch an object going away, the more its light is redshifted ?
Since light depends on the atom and on the Doppler effect, how can we know if we see the light the way we see it because of the atoms that emited it, or because of the Doppler effect ?

Nao R says:

This blew my mind… wow

ernietessein says:

I just rewatched this. Being in physics now, learning about electricity and magnetism, really opens my eyes to this video. Awesome!

vivek vr says:

i love this show. so much info in 10 mins. keep going

galeop says:

Waw this was tremendously well explained !

Daniel Benko-OperationMobiusPrime says:

i could see the difference of the reds in the two squares, but only if looked at them for a few seconds. the one on the left was darker.

Peter Timowreef says:

This episode was very illuminating.

Jhanira Renee says:

Ha. He said it'll take two hours to study. But this only took 10 minutes 😀 thanx

Fayyaz Naveed says:

Thanks to concept creator of these courses.

Write a comment