The Sounds of the Stars

Abstract

The concept of the “Music of the Spheres” is far from new; it goes back to the time of Pythagoras, and survived until a surprisingly late stage in astronomical history. Kepler, for example, took it very seriously indeed. Today everyone knows about radio waves from space, and there are people who fondly imagine that you can fit up a receiver and listen to the Pole Star. Alas, this cannot be done. Sound waves cannot travel in a vacuum, and there is very little air above a few tens of miles. On Mars, where the atmospheric pressure is very low (less than 10 mbar, against around 1,000 mbar at sea-level on Earth), even the most raucous auctioneer or football referee would struggle to make himself heard. Sound-waves are pressure waves, and depend upon a medium of some sort. The more rarefied the medium, the higher the frequency of sound waves within it. Blow up a balloon filled with the light gas helium, inhale some helium from the balloon, and your voice will be very squeaky until you clear your lungs!