Ep. 775: The Hydrogen 21-cm Line

Streamed live on Dec 15, 2025. Atomic hydrogen is the raw material for stars, but there’s a problem. It’s cold & dark, but it can do a very rare trick, releasing a photon in a very specific wavelength, known as the 21 centimeter line. And thanks to this wavelength astronomers have mapped out star forming regions across the Milky Way, the Universe and into the Dark Ages! This forbidden transition of Hydrogen has led to the mapping of galaxy rotation, a cool classroom application of quantum mechanics, and weirdly no Nobel prize. In this episode, Fraser and Pamela take a look at this line's out-of-proportion awesomeness! This show is supported through people like you on Patreon.com/AstronomyCast In this episode, we'd like to thank: Andrew Poelstra, BogieNet, Brian Cagle, Burry Gowen, David, David Rossetter, Ed, Gerhard Schwarzer, Jason Kwong, Jeanette Wink, Michael Purcell, Sergey Manouilov, Siggi Kemmler, Sérgio Sancevero

You can listen to Ep. 775: The Hydrogen 21-cm Line online on Radio and Podcast. Open the player on this page to stream the available audio.

Ep. 775: The Hydrogen 21-cm Line is an episode from 365 Days of Astronomy - Weekly Edition.

This episode is 57:00 long.

This episode was published on Dec 22, 2025.

Yes. Use the heart button on the episode page to add it to your favorite episodes list.

Yes. This page shows related episodes from 365 Days of Astronomy - Weekly Edition when more episodes are available from the podcast feed.