We're so used to the sun that we often forget what a fascinating object it really is. Far from being the dull blob that it appears from far away, it's 1030 kg of nuclear matter with temperatures ranging from 5,000 K at the surface to 107 K at the core. Some months ago, during Nordita's program on "Solar and stellar dynamos and cycles" in a talk on Helioseismology, I saw this video showing a solar quake, waves on the sun's surface:
This quake from July 1996 was triggered by a solar flare in its center that was recorded just prior to the quake. Not the newest news, but I still think this is totally amazing. There's also a lot of physics in here. Unfortunately, I wasn't able to find the real-time scale is for the video, but I think it's roughly an hour. The actual size of the image shown is 100,000 km in each direction. The data was taken with the Michelson Doppler Imager of NASA's Solar and Heliospheric Observatory (SOHO) mission which basically measures the velocity perpendicular to the sun's surface by use of the Doppler shift in spectral lines. You can find a better resolution of the picture with a brief description of the event on this website.
It is interesting to note, and you can see this on the crappy video already, that unlike water waves you'd see in a puddle, the waves on the sun's surface increase their velocity with time (by roughly factor 10 for what is shown in the video). The explanation for this is that the waves are not surface waves, but pressure waves propagating into the sun's interior. Unlike the puddle the sun is a ball and its density increases towards the middle. With increasing density, the velocity of the waves (essentially the sound velocity) increases. The waves are reflected (similar to light-reflection/refraction on planar surfaces) and appear back on the sun's surface as outgoing rings whose outward velocity increases due to the geometry of the wavefronts and the density gradient. (For more details, the interested reader is referred to astro-ph/0601006 and references therein.)
So next time you look at the sun recall it's a giant ball of plasma held together by gravity, an every-day display of fascinating physics.
See also: Light Bulbs and the Solar Energy Production
- "These smiling eyes are just a mirror for..."