1 rich Libsyn https://www.libsyn.com 90 600 Cheap Astronomy investigates why light moves at light speed in a vacuum. Hosted by Steve Nerlich. Shining a light! Dear Cheap Astronomy – Why does a photon travel at speed c, part1 It may sound a bit strange to ask why light travels at the speed of light, but that’s because c isn’t really the speed of light – it’s really a measure of the relationship between distance (or space) and time. It's become customary to call c the speed of light, but in reality light moves at different and slower speeds through air, water or glass, it only moves at c in a vacuum. &amp;nbsp; Dear Cheap Astronomy – Why does a photon travel at speed c, part1 Last week we grappled with the issue of why light is able to move at the speed c, which is around 300,000 km/sec in a vacuum. Some key points we landed were that c is actually the fastest speed that anything can move and that light isn’t the only thing that moves at c, gravity does too. The constant c is perhaps better thought of as defining the fundamental relationship between space (or distance) and time, where it must take at least one second to cross 300,000 kilometers – meaning it must take at least 0.000000033 second to cross one meter, and you can add even more zeros to cross centimeters and then nanometers. &amp;nbsp; We've added a new way to donate to 365 Days of Astronomy to support editing, hosting, and production costs.&amp;nbsp; Just visit: https://www.patreon.com/365DaysOfAstronomy and donate as much as you can! Share the podcast with your friends and send the Patreon link to them too!&amp;nbsp; Every bit helps! Thank you! ------------------------------------ Do go visit http://www.redbubble.com/people/CosmoQuestX/shop for cool Astronomy Cast and CosmoQuest t-shirts, coffee mugs and other awesomeness! http://cosmoquest.org/Donate This show is made possible through your donations.&amp;nbsp; Thank you! (Haven't donated? It's not too late! Just click!) ------------------------------------ The 365 Days of Astronomy Podcast is produced by the Planetary Science Institute. http://www.psi.edu Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. The 365 Days of Astronomy http://www.365DaysOfAstronomy.org/ <iframe title="Libsyn Player" style="border: none" src="//html5-player.libsyn.com/embed/episode/id/40863990/height/90/theme/custom/thumbnail/yes/direction/forward/render-playlist/no/custom-color/88AA3C/" height="90" width="600" scrolling="no" allowfullscreen webkitallowfullscreen mozallowfullscreen oallowfullscreen msallowfullscreen></iframe> https://assets.libsyn.com/secure/content/200768930