Description: The corona of a star is a region of extremely hot, low-density plasma surrounding the star's atmosphere, which can stretch millions of kilometers into space. Every star with a reasonably strong magnetic field, produced by a dynamo effect as charged matter moves inside the star, is expected to have a corona. Naked-eye observation of our Sun's corona is possible during a total solar eclipse, when the solar corona becomes visible as a whitish, irregularly shaped area surrounding the hidden solar disk. More generally, the shape of a star's corona is determined by the star's magnetic fields and the outward pressure of gas in its upper regions. Stellar coronas have very high temperatures: At more than a million kelvins, the solar corona is much hotter than the Sun's surface. The mechanism for heating the corona to that temperature is the subject of ongoing research, but it seems clear that the magnetic fields threading the corona play a major role. The shape of the Sun's corona changes on timescales between seconds and months, mostly in response to solar activity, such as flares ejecting plasma into the corona, or coronal mass ejections releasing a considerable amount of charged particles. It also changes on a timescale of years with what is called the solar cycle – the periodic change in strength and orientation of the Sun's magnetic field, with a period of nearly eleven years. Changes of this kind are expected to occur in an analogous fashion in other stars' coronas, as well.

Related Terms:

• Chromosphere
• Solar Flare
• Solar Prominence
• Solar Wind
• Stellar Structure

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".