WAVES AND THE SUN Electromagnetic radiation The Sun emits, not just visible light, but light from all across the electromagnetic spectrum - from radio waves to gamma-rays. Sound waves Sound waves can travel through all media: air, walls, and even the Earth itself (earthquakes). The speed with which the waves travel is the sound speed, and it depends on both the temperature and density of the medium in which it travels. Sound waves are extemely important on the Sun as welll Helioseismology Seismology is the study of earthquakes and is done by measuring the vibrations of the Earth's surface. Helioseismology is a comparatively new field of science (begun in the 1970s) whereby vibrations of the Sun's surface are measured. The vibrations are measured from the light emitted by the Sun's surface, and the problem has certain similarities to that of standing waves in a string As you go closer to the Sun's center the sound speed increases as T1/2. Any wave that is going from the surface to the center is forced to curve and eventually head back towards the surface. As the wave is confined by two boundaries, standing waves are set up By making a model of the Sun, one can predict what sort of vibrations are expected, which can then be compared with what is measured.