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Glossary term: Sun

Description: The Sun is the star that is closest to Earth. For astronomers, it is a star of type "G2V", which means it is not very bright compared to other stars, and, at a surface temperature ("effective temperature") of 5500 degrees Celsius, neither very cold nor very hot for a star. For astronomers, the Sun is interesting because we can observe it much more closely than any other star. We can make out small details showing what is known as solar activity, which is related to the Sun's magnetic fields: sunspots (cooler areas), flares (short-lived bright flashes) and even coronal mass ejections (electrically charged particles flung away from the Sun). Physicists have also detected elementary particles known as neutrinos from the Sun's core; this is direct evidence for nuclear fusion processes.

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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

The Sun, surrounded by several bright circles and arcs, over a snowy, tree-lined landscape.

Winter Haloes, by Thomas Gigl, Germany

Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Sun/Moon haloes. Captured in Jochberg located in the famous Austrian ski-region of Tirol, this image shows multiple features related to ice halos, which are a more common appearance around the sun, due to its brightness, than the moon. External and internal reflection of sun rays from ice crystal faces and within different types of ice crystals lead to these halo related phenomena. The 22° halo encircles the sun, with two bright spots at the edge called Sundogs, Parhelia or Mock Suns observed to the left and right at the same height as the sun. The horizontal white band called the parhelic circle, named after the sun god Helios, passes through the sun and the Sundogs at the same angular elevation. An Upper tangent arc, a suncave parry arc and a lower tangent arc are also seen touching the top and bottom of the 22° halo. An upside down rainbow like arc or the circumzenithal arc is seen touching the bright supralateral arc, both of which are less frequently observed.
Credit: Thomas Gigl/IAU OAE
License: CC-BY-4.0 Creative Comments Attribution 4.0 International (CC BY 4.0) icons
Image showing groups of sunspots as dark patches which lie in bands above and below the Sun's equator

Sunspots

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