Since sound does not
travel through vacuum, how can the astronauts communicate from space to earth?
How do astronauts communicate with each other?
Sound
cannot travel through the vacuum of space, but visible light and other forms of
electromagnetic radiation can. One of these forms is commonly called radio. The
astronauts have devices in their helmets which transfer the sound waves from
their voices into radio waves and transmit it to the ground (or other
astronauts in space). This is exactly the same as how your radio at home works.
Radio waves are often thought of as a form of sound because of their use in
this way, but radio waves are NOT sound waves - they are a form of
electromagnetic radiation analogous to visible light, and therefore can
propagate through a vacuum.
http://curious.astro.cornell.edu/physics/151-people-in-astronomy/space-exploration-and-astronauts/human-spaceflight-current-or-past/944-how-do-the-astronauts-communicate-in-space-if-sound-cannot-travel-in-a-vacuum-beginner
