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.
Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.