helioseismology

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helioseismology

(heel-ee-oh-sÿz-mol -ŏ-jee) The study of the Sun's interior by the observation of solar oscillations. First detected in 1960 by measuring the Doppler shifts of Fraunhofer lines at several points on the Sun's disk away from active regions, the oscillations are a rhythmic rise and fall of regions of the solar photosphere (and lower chromosphere) several thousand kilometers in diameter. They have periods of about 5 minutes, persist at any one point for less than half an hour, and attain a maximum velocity of about 0.5 km s–1. The oscillations are thought to be produced by the outward propagation of low-frequency sound waves, generated by turbulence in the convective zone, and by analyzing their global occurrence over an extended period of time it is possible to build up a picture of the Sun's interior.

Instruments used in the observation of solar oscillations include grating spectrographs, narrow-band interference filter (Lyot filter, magneto-optical filter, or Fabry–Perot interferometer) imagers, and Michelson interferometers – notably the Fourier tachometer, which has been in operation since 1985 and simultaneously monitors more than 60 000 points on the Sun's disk. A number of collaborative programs have been established, for example the Global Oscillations Network Group (GONG). These are complemented by continuous monitoring by the helioseismology instrument on ESA's spacecraft, the Solar Heliospheric Observatory (SOHO).

helioseismology

[‚hē·lē·ō‚sīz′mäl·ə·jē]
(astronomy)
The analysis of wave motions of the solar surface to determine the structure of the sun's interior.
References in periodicals archive ?
Unlike the small-scale, convection-driven disturbances known to continually vibrate the Sun from within (June issue, page 18), solar-flare sunquakes deliver their acoustic energy in powerful but short-lived bursts.
Some of that heat excites the Corona, or outer atmosphere of the sun, but a portion generates a shock wave that hammers the surface and produces a sunquake.
Among the topics are particle acceleration in flares, the continuity equation approach to electron-beam precipitation, hydrodynamic response to particle injection, microwave emission and polarization, non-thermal hydrogen emission caused by electron beams, and sunquakes associated with solar flares.
Also very highly recommended for personal, professional, academic, and community library Astronomy collections are Professor Zirker's previous works: "Total Eclipses of the Sun" (Princeton University Press, 9780691029528, $3.95) ; "Journey from the Center of the Sun" (Princeton University Press, 9780691118482, $24.95); "Sunquakes: Probing the Interior of the Sun" (Johns Hopkins University Press, 9780801874192, $35.00); and "An Acre of Glass: A History and Forecast of the Telescope" (Johns Hopkins University Press, 9780801882340, $30.00).