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Research | Space Research | Space Plasma Physics - Solar wind - SWAN - Science
SWAN - Science
The solar system travels continuously through the interstellar gas cloud. Therefore, hydrogen atoms flow into the solar system from a certain direction of the sky. A solar Lyman alpha radiation is scattered by these neutral hydrogen atoms. SWAN measures this scattered Lyman alpha (UV) radiation. Observations covering the whole sky have been made since January 1996. The results can be accessed via the French SWAN web site or via the direct links in the right column of this page.
Physics behind the anisotropies
Hydrogen atoms collide with solar wind protons and get ionised. The ionisation cavity around the Sun is formed and the shape of it depends on the solar wind latitudinal distribution. The shape of the cavity and, further, on the solar wind latitudinal distribution can be deduced from the interplanetary (IP) Lyman alpha resonance glow. The work for achieving a better understanding is in progress.
If the solar wind were isotropic, the hydrogen distribution and the Lyman alpha emission pattern would be axisymmetric around the direction where the interplanetary hydrogen flows into the solar system. However, this is not true. The Lyman alpha pattern is not axisymmetric and the departures from the axisymmetry are caused by the the latitudinal variation of the solar wind.
More information:
, tel. +358 9 1929 4640
, tel. +358 9 1929 4658
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