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 ?
A bright young Sun consistent with helioseismology and warm temperatures on ancient Earth and Mars.
However, solar oblateness does not depend on the use of helioseismology for its determination ([section]4.
This also applies to theoretical results which attempt to extract helium levels from helioseismology [156].
Preliminary indications are that the standard solar model, to the accuracy to which we need it for predicting neutrino fluxes, has been verified as far as helioseismology can presently go," Bahcall says.
Helioseismology, as this relatively new discipline is called, requires large numbers of precise observations made continuously for days at a time.
The European Space Agency's Solar and Heliospheric Observatory, scheduled for launch in 1994, will carry three helioseismology instruments (SN: 2/22/86, p.
Helioseismology demonstrates that the Sun acts as a resonant cavity [53].
New solar opacities, abundances, helioseismology, and neutrino fluxes.
Currently, much of the support for the gaseous models of the Sun arises from helioseismology [15] or the study of solar quakes on the surface of the Sun.