An Etymological Dictionary of Astronomy and Astrophysics
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That part of the Milky Way galaxy lying near the Sun. In fact there is no definition of the exact radius of this region. It is referred to the immediate solar neighborhood (within about 5 pc), the solar neighborhood (within about 25 pc), and the extended solar neighborhood (within a few hundred pc).

→ solar; → neighborhood.

A neutrino generated in the → Sun. The main source of solar neutrinos is the → proton-proton chain of reactions: 4 × p→ He + 2e⁺ + 2ν_e, in which an energy of +28 MeV is shared between the reaction products. These are called → low-energy neutrinos. There are less important reactions in the Sun yielding a smaller flux of higher energy neutrinos. The solar neutrino flux can be estimated from the → solar luminosity (L), as follows Since there are two neutrinos for each 28 MeV of energy, the neutrino flux at the Earth distance (d) is given by: ν flux = 2Lsun/(28 MeV) × (1/4πd²) = 6 × 10¹⁰ cm^-2 s^-1. See also the → solar neutrino problem.

→ solar; → neutrino; → flux.

A major discrepancy between the flux of neutrinos detected at Earth from the solar core and that predicted by current models of solar nuclear fusion and our understanding of neutrinos themselves. The problem, lasting from the mid-1960s to about 2002, was a considerably lesser detected number of neutrons compared with theoretical predictions. The discrepancy has since been resolved by new understanding of neutrino physics, requiring a modification of the → standard model of particle physics, in particular → neutrino oscillation.

→ solar; → neutrino; → problem.

A measure of the flux of neutrinos from the Sun reaching the Earth. 1 SNU is equal to 10^-36 solar neutrinos captured per target atom per second.

→ solar; → neutrino; → unit.

A → European Space Agency (ESA) mission with strong → National Aeronautics and Space Administration (NASA) participation aimed at studying the Sun up close and from high latitudes, launched on 10 February 2020. Solar Orbiter is equipped with 10 instruments and will provide the first images of the Sun's poles. It will make a close approach of the Sun every six months. Its distance from the Sun varies from within the orbit of → Mercury to close to the orbit of Earth. At closest approach, Solar Orbiter will be about approximately 42 million km from the Sun. Solar Orbiter will combine in situ measurements of the → solar wind around the spacecraft with remote sensing, looking at the Sun's features from afar, to connect the two together. The spacecraft has been tested to withstand temperatures up to 500 °C -- enduring thirteen times the amount of solar heating that satellites in Earth's orbit experience. Solar Orbiter will help us understand how our star creates and controls the → heliosphere, i.e. the giant bubble of → plasma that surrounds the whole → Solar System and influences the planets within it.

→ solar; → orbiter.

The angle subtended (8''.79) by the → equatorial radius of the Earth at a distance of 1 → astronomical unit.

→ solar; → parallax.

The abundance of a → chemical element as determined from the observation of solar → spectral lines. The solar chemical composition is an important ingredient in our understanding of the formation, structure and evolution of both the Sun and our solar system. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared (Asplund et al. 2009, arXiv:0909.0948). The photospheric abundances relative to hydrogen are not representative of the → protosun, or global → solar system abundances. This is because heavy-element fractionation in the Sun has altered photospheric abundances (Lodders 2003, ApJ 591, 1220).

→ solar; → photospheric; → abundance.

The branch of astrophysics concerned with the study of the physical properties of the Sun based on the most detailed observations which can be obtained for a star.

→ solar; → physics.

Any power obtained by converting solar radiation into useful power.

→ solar; → power.

A space probe designed to gather data about the Sun.

→ solar; → probe.

A large, arch-shaped filament of hot gas extending outward from the Sun's surface. More at → prominence.

→ solar; → prominence.

All the constituents making up the Sun's emission: photons, electrons, protons, neutrinos, and atomic nuclei.

→ solar; → radiation.

The → radiation pressure of solar photons, which pushes a comet's dust outward to form a → dust tail.

→ solar; → radiation; → pressure.

Plural form of → solar radius.

→ solar; → radii.

A unit of length, representing the radius of the → Sun, used to express the size of stars in astrophysics. It is equivalent to: 695,700 km, 0.00465047 → astronomical units, 7.35355 × 10^-8 → light-years, and 2.32061 → light-seconds.

→ solar; → radius.

The motion of the Sun around an axis which is roughly perpendicular to the plane of the → ecliptic; the Sun's rotational axis is tilted by 7.25° from perpendicular to the ecliptic. It rotates in the → counterclockwise direction (when viewed from the north), the same direction that the planets rotate (and orbit around the Sun). The Sun's rotation is differential, i.e. the period varies with latitude on the Sun (→ differential rotation). Equatorial regions rotate in about 25.6 days. The regions at 60 degrees latitude rotate more slowly, in about 30.9 days.

→ solar; → rotation.

A space vehicle designed to orbit about the Sun.

→ solar; → satellite.

The spectrum of the Sun's electromagnetic radiation, consisting of a continuum spectrum marked with dark absorption lines.

→ solar; → spectrum.

The collective name for the Sun and all objects gravitationally bound to it. These objects are the eight planets, their 166 known moons, five dwarf planets, and billions of small bodies. The small bodies include asteroids, icy Kuiper belt objects, comets, meteoroids, and interplanetary dust. The solar system is roughly a sphere with a radius greater than 100,000 AU. Planets, satellites, and all interplanetary material together comprise only about 1/750 of the total mass. Geochemical dating methods show that the solar system chemically isolated itself from the rest of the Galaxy (4.7 ± 0.1) × 10⁹ years ago.

→ solar; → system.

Same as → protosolar abundance.

→ solar system; → abundance.