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<-   The spectrum of the Sun   ->
Fourier spectrum of the intensity variations of the Sun, observed with the experience VIRGO of the SOHO satellite, continously during 600 days.
Crédit : Paris Observatory.

For more than twenty years, scientists have tried to observe the Sun continuously. Instruments on the ground and in space (SOHO satellite) study the vibrations of the Sun.

Now, millions of modes have been detected, with frequencies between 2 and 5 milliHertz (periods close to 5 minutes). These frequencies are much lower than those that our ears can hear.

The amplitudes of these modes are very weak, a few millionths in photometry and a few centimeters per second in spectroscopy.

This huge set of data, interpreted using sismology theories, allows us to understand the internal structure of the Sun with high accuracy.

Sismology is the perfect tool to "observe" the interior of the stars. This technique consists of detecting and measuring the features of the proper oscillation modes of the stars, and using these properties to to understand the internal structure, as it is carried out for a long time in the case of the Earth or the moon.

  • The theory is well known. It benefits from old developments in Geophysics, and it uses mechanics and thermodynamics.
  • In principle, it allows us to probe the internal structure of an object, interpreting its frequency spectrum.
  • Concerning the stars, sismology is the only way to study their interior.