Astronomy and Space

Alfvén surface

The Alfvén surface is the boundary separating a star's corona from the stellar wind defined as where the coronal plasma's Alfvén speed and the large-scale stellar wind speed are equal. It is named after Hannes Alfvén, and is also called Alfvén critical surface, Alfvén point, or Alfvén radius. In 2018, the Parker Solar Probe became the first spacecraft to cross the Sun's Alfvén surface.

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• ▸Domestic policy of the George W. Bush administration
• ▸COVID-19 vaccination in Malaysia
• ▸Double star

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