Solar flares, coronal mass ejections and other energetic phenomena in the Sun can have a major impact on the Earth, sometimes knocking out telecommunications and power transmission systems. The particles and radiation released by these events are also hazardous for astronauts and spacecraft. A major goal in solar physics, therefore, is to be able to predict this so-called space weather. Now two US researchers have shown how helioseismology - the study of how the Sun vibrates or oscillates - can be used to detect these phenomena on the far side of the Sun. Since the Sun rotates with a period of 27 days, the ability to look at its far side might allow such events to be predicted a week before their effects will be experienced on earth (Science 287 1799).
Charles Lindsey of the Solar Physics Research Corporation in Arizona and Douglas Braun of Northwest Research Associates in Colorado used data from a Doppler imager on the Solar Heliospheric Observatory (SOHO) to measure ripples on the surface of the Sun. In standard helioseismology measurements of the motion of the surface are used to reveal what is going on inside the Sun, just as standard seismology is used to learn more about the interior of the Earth. Lindsey and Braun used a technique called two-skip phase-sensitive holography to study the far side of the Sun. In addition to predicting space weather, the technique should lead to a better understanding of the acoustic properties of the Sun’s magnetic regions and of the Sun as a whole.
