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.
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.
This also applies to theoretical results which attempt to extract helium levels from helioseismology [156].
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 can measure the speed of sound--and therefore temperatures, motions, and chemical compositions--anywhere in the solar interior by analyzing the millions of frequencies of tiny surface oscillations, most with periods around 5 minutes.
Helioseismology demonstrates that the Sun acts as a resonant cavity [53].
The fundamental papers include Edwin Hubble's study of "spiral nebulae," Grote Reber's pioneering foray into radio astronomy, Fred Hoyle's explanation of nucleosynthesis inside stars, George Abell's study of galaxy clusters, Arno Penzias and Robert Wilson's discovery of the cosmic background radiation, and Roger Ulrich's presentation on helioseismology.
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.
By monitoring sound waves that course through the Sun, the exploding field of helioseismology is giving us revolutionary insights into the structure and dynamics of the solar interior (S&T: October 1996, page 20).
In his view, studies like Pijpers's put helioseismology, not general relativity, to the test.
Thus, we hear nothing of optical interferometers, helioseismology, or high-redshift supernova discoveries.
A burgeoning solar science called helioseismology has come to the rescue and is now starting to yield some of the Sun's secrets.