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 ?
Helioseismology has been extended to the outer solar atmosphere [214,369-372].
"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.
The study of the inner sun, known, as helioseismology (SN: 7/2/88, p.8), has measured its rotation rate about 80 percent of the way to the center, Rust says, and the Analyzer might add another 10 percent.
Gough had already suggested that helioseismology could be used to help establish fractional abundances: " Thus one might anticipate inferring the hydrogen-helium abundance ratio by comparing the measured values with a sequence of model solar envelopes" [19, p.
Papers are grouped in sections on instrumentation, convection and sunspots, magnetism of quiet sun and active regions, waves and shocks, chromospheric heating, coronal heating, local helioseismology, emerging flux, reconnection, flares, coronal mass ejections, and solar wind.
Powerful solar observatories in space such as Yohkoh, the Solar and Heliospheric Observatory, (SOHO), and the Transition Region and Coronal Explorer (TRACE), along with new techniques in helioseismology, are giving astronomers the best-ever views of our home star.
Helioseismology, as this relatively new discipline is called, requires large numbers of precise observations made continuously for days at a time.
Supportively, helioseismology reveals that sound waves travel much faster through sunspots than through normal photospheric matter [91,92].
Now we can observe deep layers right down to the core using helioseismology, the study of the super-low-frequency sound waves that course through the Sun and subtly manifest themselves on its surface.
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.