Helioseismology

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Another probe of the Sun's interior uses the pulsating motions of the Sun. The pulsations are too small to be seen just by looking at the Sun. But the pulsations can be seen if the doppler shifts are measured across the face of the Sun. Some parts of the Sun expand towards the Earth and adjacent regions contract away from the Earth. These regions are several thousands of kilometers across and the pulsation periods are just a few minutes long. Different types of oscillating waves combine to produce the complicated patterns of pulsation seen.

One type of pulsation is shown here. The blue regions are approaching and the red regions are receding from you. The pulsations are thought to extend far into the Sun's interior (courtesy of the National Solar Observatory).

If you disentangle the different oscillation modes from each other, you can use these waves to probe the solar interior. How those waves propagate through the Sun and interact with each other depends on the temperature, density, and composition of the material they pass through. By observing the effects of these waves on the photosphere of the Sun, you can determine the temperature, density, and composition of the different layers inside the Sun. Geologists on the Earth use similar techniques to study the interior of our planet from earthquake waves in the research field called seismology. Modifying the name for solar studies, the study of the Sun's interior using the solar oscillations is called helioseismology.

Solar astronomers have set up a global network of stations to continuously monitor the Sun's pulsations. This network is called the Global Oscillations Network Group (GONG). Links to web sites describing GONG and other helioseismology sites are given below. Instruments to detect solar oscillations have also been placed on satellites. Check the links below for more information about them.

Links to Centers Probing the Sun's Interior

1. The GONG homepage at the National Optical Astronomy Observatories is a must see. A concise fact sheet for GONG is available, as well as, information about helioseismology in general.
2. The Solar Oscillations Investigation at Stanford is another major center for helioseismology research.
3. The Stanford group have also constructed an excellent resourse site for K-12 students called The Solar Center. Many educational activities are available, along with excellent images, movies, and audio (yes, you can hear the Sun pulsate!---the doppler observations have been converted into sound).
4. The Marshall Space Flight Center's Solar Physics web site is an excellent starting point for all the research about the Sun. Links to the space missions and the science background about the Sun are given here.

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last updated: November 25, 2007