Sun

The Sun is the star located at the centre of the Solar System. It is a massive sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light and infrared radiation with 10% at ultraviolet energies. It is the main source of energy for life on Earth. The Sun has been an object of veneration in many cultures and a central subject of astronomical research since antiquity.

standard unit of mass in astronomy which is equal to 1.98892 × 10³⁰ kg

thumb|right|The Sun, as seen from low Earth orbit overlooking the International Space Station. This sunlight is not filtered by the lower atmosphere, which blocks much of the solar spectrum.

natural phenomenon when daylight lasts for more than 24 hours, occuring only inside or close to the polar circles

thumb|upright=1.2|Wearing sunglasses under direct sunlight: Large lenses offer good protection, but broad temple arms are also needed against "stray light" from the sides.

unit of measurement

atmospheric optical phenomenon

conversion of energy from sunlight into electricity

unit of radiant flux in astronomy

thumb|The light from the lamp (1.) functions as a detectable change in the plant's environment. As a result, the plant exhibits a reaction of phototropism—directional growth (2.) toward the light stimulus. thumbnail|Auxin distribution controls phototropism. 1. Sunlight strikes the plant from directly above. Auxin (pink dots) encourages growth straight up. 2, 3, 4. Sunlight strikes the plant at an angle. Auxin is concentrated on one side, stimulating growth at an angle from the preceding stem. thumb|Phototropism in Solanum lycopersicum.

intensity of sunlight

rays of sunlight that appear to radiate from the point in the sky where the sun is located

bright spot

convection cell in the photosphere of a star

Helioseismology is the study of the structure and dynamics of the Sun through its oscillations. These are principally caused by sound waves that are continuously driven and damped by convection near the Sun's surface. It is similar to geoseismology, or asteroseismology, which are respectively the studies of the Earth or stars through their oscillations. While the Sun's oscillations were first detected in the early 1960s, it was only in the mid-1970s that it was realized that the oscillations propagated throughout the Sun and could allow scientists to study the Sun's deep interior. The term was

special purpose telescope used to observe the Sun

apparent mystery that the early Earth seems to have had liquid water, even though the young Sun was less bright, thus presumably completely freezing the Earth

boundary between a magnetosphere and an ambient magnetized medium, for example when the solar wind encounters the magnetic field of Earth

300px|thumb|right|Heliometer at the Kuffner observatory (Vienna, Austria) alt=Brass Heliometer Split lens (glass lens held in brass housing, with split down the middle, and screw mechanism to move one half relative to the other)|thumb|Heliometer split lens, displayed at Custer Observatory, Long Island, New York. A heliometer (from Greek 'sun' and 'measure') is an instrument originally developed from the mid-eighteenth to early nineteenth centuries for measuring the variation of the Sun's diameter at different seasons of the year, but the modern version of the instrument is capable of much wide

major discrepancy between measurements of the numbers of neutrinos flowing through the Earth and theoretical models of the solar interior

thumb|upright=1.5|This image presents various wavelengths of light produced by the Sun.

Section of Sun's atmosphere

structure in the lower corona and transition region of the Sun

Solar radiation scattered and absorbed in Earth's atmosphere

thumb |400px |Daisies (Bellis perennis) face the Sun after opening in the morning and will follow the Sun through the day. Heliotropism, a form of tropism, is the diurnal or seasonal motion of plant parts (flowers or leaves) in response to the direction of the Sun.

branch of astrophysics

the pattern of rotation of components of the Sun

physical process that generates a star's magnetic field

neutrinos produced in the core of the sun through various nuclear fusion reactions

thumb|The solar disk observed in four different wavelengths of ultraviolet radiation by the Atmospheric Imaging Assembly spectroheliograph on board the [[Solar Dynamics Observatory. From left to right, the wavelengths imaged are 171, 304, 335, and 94 Å. Colors are false and added in postprocessing.]] The spectroheliograph is an instrument used in astronomy which captures a photographic image of the Sun at a single wavelength of light, a monochromatic image. The wavelength is usually chosen to coincide with a spectral wavelength of one of the chemical elements present in the Sun.

Jewish blessing, thanking God for creating the sun, recited when the sun completes its cycle every 28 years on a Tuesday at sundown

tropical solar phenomenon

Apparent location of the Sun in the sky

surface shaking on interstellar bodies in general

type of eye-wear used to view the sun

angle between the zenith and the centre of the Sun's disc

circle of latitude

form of astrology, commonly found in newspapers, which considers only the position of the Sun at birth, placed within one of the twelve zodiac signs, which is then related to the current movements of all the planets

sunward-traveling plasma voids observed in the Sun’s outer atmosphere

heraldic figure

thumb|alt=A man with his back to the camera stares directly at a twilight sun.|A man sungazing

The transit of an astronomical object in front of the Sun from the Earth's perspective

sparkling light formed when sunlight reflects from water waves

thumb|Sunbeams in Nevada during a sunset thumb|Daytime sunbeams as seen from the ISS, illustrating their parallel nature A sunbeam, in meteorological optics, is a beam of sunlight that appears to radiate from the position of the Sun. Shining through openings in clouds or between other objects such as mountains and buildings, these beams of particle-scattered sunlight are essentially parallel shafts separated by darker shadowed volumes. Their apparent convergence in the sky is a visual illusion from linear perspective. The same illusion causes the apparent convergence of parallel lines on a lon

Branch of solar physics and aeronomy

thumb|A close-up of one of the loop brightenings. The frame on the far right is the most zoomed in, showing the putative nanoflare. thumb|"This false-color temperature map shows solar active region AR10923, observed close to center of the sun's disk. Blue regions indicate plasma near 10 million degrees K." Credit: Reale, et al. (2009), NASA.

Brightenings in the Sun's chromosphere

device that provides illumination approximating natural sunlight

Azimuth angle of the Sun's position

Technique of studying the Sun's corona