Glossary term: stellar activity

Also known as solar activity

Description: Activity is a collective term for the different effects magnetic fields have on stars. Stars with strong magnetic fields have more starspots on their surface. Stellar magnetic fields are also likely to be the source of heat for the corona of a star so stars with stronger magnetic fields will have more X-ray and ultraviolet emission from their corona. Activity can also be seen in the spectrum of the star, particularly emission from the hydrogen alpha line. Taken together these effects loosely quantify the "activity" of a star. Massive stars (with spectral type O, B and early A) typically have low activity. Activity then increases for lower mass stars, peaking at red dwarfs (M dwarfs). Young stars are more active than old stars. The Sun follows an 11 year activity cycle.

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Term and definition status: This term and its definition is still awaiting approval

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".

Related Media

Image showing groups of sunspots as dark patches which lie in bands above and below the Sun's equator


Caption: In this image the sun peppered with groups of sunspots over almost nine days between July and August 2012. The sunspots seen in this image have been sources of the solar flares and coronal mass ejections (CME). In this image particulary, the sun is approaching solar maximum in its cycle (solar cycle), where we see many spots forming along the suns' equator. These sunspots and activity are seen in the southern hemisphere, before then most of the activity was on the northern hemisphere.
Credit: NASA/SDO/HMI credit link
License: PD Public Domain icons
The Sun in ultraviolet appears as a circle. The flare is a bright patch in the upper right 3/4 of the way from the center

Solar flare

Caption: This image shows the mid-level solar flare that was observed in March 2022 by the Solar Dynamic Observatory (SDO). The SDO observes the Sun activity, hence it shows the regions on the Sun where there is activity. A solar flare is brief brightening on the sun's surface, this particular flare is an M-class, which means that it is a tenth of the size of the most intense flares, namely the X-flares. Solar flares are barely visible with the naked eye, thus the SDO. The image here, is captured in extreme ultravoilet light that was colourized by red in the SDO, the flare appears in the upper of the solar disk.
Credit: NASA/SDO credit link
License: PD Public Domain icons