Glossary term: Sun

Description: The Sun is the star that is closest to the Earth. For astronomers, it is a star of type "G2V". This means the Sun is a main sequence star with a typical temperature ("effective temperature") of 5800 kelvins (K). Main sequence stars are stable, with energy released by hydrogen fusion in their core balancing the inwards force due to gravity. The Sun appears white to the human eye as it emits lots of light all across the visible spectrum. When lower in the sky, increased atmospheric extinction can make the Sun appear yellow or orange, hence its common depiction as yellow. Stars range from more than 1000 times brighter than the Sun to some 1000 times fainter, but the brighter ones are relatively rare: the Sun is brighter (and heavier) than most (perhaps some 85%) of the stars in the Galaxy.

For astronomers, the Sun is interesting because of its proximity, which means that the surface can be resolved in greater detail, allowing structures and phenomena to be studied. For example, detailed studies of solar activity, which is related to the Sun's magnetic fields, can include: 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. The element helium was first detected in the solar spectrum, hence the name helium, which comes from Helios (in Greek mythology the Sun god).

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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".

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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 Commons Attribution 4.0 International (CC BY 4.0) icons

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

Related Activities

Measure the Solar Diameter

astroEDU educational activity (links to astroEDU website)
Description: Hands-on activity to measure the Sun by using household materials.

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
Tags: Hands-on , Scales , Observing , Measurement
Age Ranges: 12-14 , 14-16 , 16-19 , 19+
Education Level: Middle School
Areas of Learning: Social Research
Costs: Low Cost
Group Size: Group
Skills: Communicating information , Constructing explanations , Using mathematics and computational thinking

Counting Sunspots

astroEDU educational activity (links to astroEDU website)
Description: Counting the Sunspots using real solar images and data.

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
Tags: Hands-on , Sunspots , Data analysis
Age Ranges: 16-19
Areas of Learning: Observation based
Costs: Low Cost
Duration: 1 hour
Group Size: Group
Skills: Analysing and interpreting data , Constructing explanations , Using mathematics and computational thinking

Meet Our Neighbours: Sun

astroEDU educational activity (links to astroEDU website)
Description: Explore the tactile version of our star; the Sun with household materials.

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
Tags: Hands-on , Model , Sunspots , Visually Impaired , Tactile
Age Ranges: 6-8 , 8-10 , 10-12
Education Level: Middle School , Primary , Secondary
Areas of Learning: Interactive Lecture , Modelling
Costs: Low Cost
Duration: 1 hour
Group Size: Group
Skills: Analysing and interpreting data , Developing and using models

Build a Safe Sun Viewer

astroEDU educational activity (links to astroEDU website)
Description: Build a safe Sun viewer using cheap household items and learn why it is dangerous to look directly at the Sun, even briefly.

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
Tags: Hands-on , Safety
Age Ranges: 6-8 , 8-10 , 10-12
Education Level: Primary , Secondary
Areas of Learning: Modelling , Observation based
Costs: Low Cost
Group Size: Group
Skills: Planning and carrying out investigations

Solar System Model

astroEDU educational activity (links to astroEDU website)
Description: Make a model of the Solar System planets using household materials.

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
Tags: Hands-on , Model , Planets
Age Ranges: 4-6 , 6-8 , 8-10
Education Level: Pre-school , Primary
Areas of Learning: Modelling
Costs: Low Cost
Duration: 30 mins
Group Size: Group
Skills: Analysing and interpreting data , Asking questions , Communicating information , Developing and using models

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