An Etymological Dictionary of Astronomy and Astrophysics
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→ Orion's Belt.

→ belt; → Orion.

A pink to brownish border above the horizon separating the Earth's dark shadow on the sky from the sky above it. The Belt of Venus appears during a cloudless twilight just before sunrise or after sunset. It is due to scattered red sunlight in the atmosphere. Also called anti-twilight arc.

→ belt, → Venus.

A → European Space Agency (ESA) mission aimed at studying → Mercury, the least explored planet in the inner → Solar System. It was launched on 20 October 2018. Among several goals, BepiColombo will make a complete map of Mercury at different wavelengths. It will chart the planet's → mineralogy and elemental → composition, determine whether the interior of the planet is molten or not, and investigate the extent and origin of Mercury's → magnetic field, the properties of its → magnetosphere, and history of the planet. The trajectory will also be modified by eight planetary flybys: of Earth in April 2020, Venus in 2020 and 2021, and then six times of Mercury itself between 2021 and 2025. BepiColombo will enter Mercury orbit in December 2025. BepiColombo is a joint mission between ESA and the Japanese Aerospace Exploration Agency (JAXA), executed under ESA leadership.

Named after Giuseppe (Bepi) Colombo (1920-1984), a scientist who studied Mercury's orbital motion in detail as well as orbits and interplanetary travel in general.

→ Coma Berenices.

The equation expressing → Bernoulli's theorem: P + (1/2)ρV² + ρgz = constant, where P is the fluid → pressure, V is → velocity, ρ is → density, g is the acceleration due to → gravity, and z is the vertical reference → level. The theree terms are called → static pressure, → dynamic pressure, and → hydrostatic pressure, respectively. The Bernoulli equation states that the total pressure along a → streamline is → constant.

→ Bernoulli's theorem; → equation.

A statement of the → conservation of energy in the → steady flow of an → incompressible, → inviscid fluid. Accordingly, the quantity (P/ρ) + gz + (V²/2) is → constant along any → streamline, where P is the fluid → pressure, V is the fluid → velocity, ρ is the mass → density of the fluid, g is the acceleration due to → gravity, and z is the vertical → height. This equation affirms that if the internal velocity of the flow goes up, the internal pressure must drop. Therefore, the flow becomes more constricted if the velocity field within it increases. Same as the → Bernoulli equation.

After Daniel Bernoulli (1700-1782), the Swiss physicist and mathematician who put forward the theorem in his book Hydrodynamica in 1738; → theorem.

1) A small, round fruit on particular plants and trees.
2) Botany: Any of various small edible fruits such as the raspberry, blackberry, and strawberry.

M.E. berye, from O.E. berie "berry, grape," cf. M.Du. bere, Ger. Beere, O.Sax. winberi, Gothic weinabasi "grape," Norwegian and Danish bær, of unknown origin.

Pelâr, from Hamadâni, Malâyeri pellâr, pellâra "berry, grape berry;" cf. Laki, Xonsâri palâra "raisin grape," Aligudarzi pellâr "part of a raison grape," of unknown origin (related to berry, as above?).

A grey, very hard metallic chemical element; symbol Be. → Atomic number 4; → atomic weight 9.01218; → melting point about 1,278°C; → boiling point 2,970°C (estimated); → specific gravity 1.85 at 20°C; → valence +2. Beryllium occurs as beryl, from which it is obtained by electrolysis. Used for light alloys which are corrosion resistant. Beryllium was discovered by Louis Nicolas Vauquelin (1763-1829) in 1798. First isolated by Friedrich Wöhler (1800-1882) in 1828.

From L. beryll(us), from beryl, a mineral, beryllium aluminum silicate, Be₃Al₂Si₆O₁₈, M.E. beril, from O.Fr., from L. berillus, from Gk. beryllos, + → -ium.

From Friedrich Wilhelm Bessel (1784-1846), German astronomer and mathematicians, who made fundamental contributions to positional and spherical astronomy.

A linear second-order differential equation, the solutions to which are called Bessel functions.

From → Bessel; → equation

Hamugeš, → equation.

Same as → 61 Cygni, the first star whose distance was measured, by Friedrich Bessel in 1838.

→ Bessel; → star.

Of or pertaining to Friedrich Wilhelm Bessel (1784-1846) or to his discoveries. → Besselian day number → → Bessel equation → Besselian star constant → → Besselian year.

→ Bessel.

Any of the five quantities denoted by A, B, C, D, and E used in conjunction with → Besselian star constants for the reduction of a star's → mean catalog place to its → apparent place.

→ Besselian; → day; → number.

Any of the eight quantities denoted by a, b, c, d (for → right ascension) and a', b', c', d' (for → declination) used in conjunction with → Besselian day numbers for the reduction of star's → mean catalog place.

→ Besselian; → star; → constant.

The period taken for the right ascension of the mean Sun to increase by 24 hours. The starting point is when the mean Sun's longitude is 280°, corresponding roughly to January 1. It is virtually the same as the tropical year.

→ Besselian; → year.

In a scatter plot, a mathematical line or curve that passes as near to as many of the data points as possible.

Best, M.E., from O.E. betst, akin toi O.E. bot "remedy." Fit, from M.E. fitten "to marchal troops," from or akin to M.Dutch vitten "to be suitable."

Behtarin supperlative of beh "good, fine" (Mid.Pers. veh "better, good," O.Pers. vahav-, vahu-, Av. vah-, vohu- "good," cf. Skt. vasu- "good," Hittite wasu-, Gaulish vesus "good") + saz, from sazidan "to be fit, proper," from Mid.Pers. saz, sazistan "to be fitting, proper."

The brightest star in the constellation → Andromeda with an average → apparent visual magnitude of 2.05. It is a red (B - V = +1.57), → giant star of → spectral type M0 III. Beta And lies at a distance of 197 ± 7 → light-years (61 ± 2 → parsecs). It has a mass of 3-4 Msun (→ solar mass), a → luminosity of ~ 2,000 Lsun (→ solar luminosity), and a radius of 100 Rsun (→ solar radius). Its other designations include: Mirach, Merach, Mirac, Mizar, 43 Andromedae, BD+34°198, HD 6860, HIP 5447, HR 337, LTT 10420, and SAO 54471. Beta And happens to lie nearly along the → line of sight to the galaxy → NGC 404. This galaxy, known as → Mirach's Ghost, is visible seven arc-minutes away.

Beta, a Greek letter of alphabet used in the → Bayer designation; → Andromeda

The second brightest star in the constellation → Cepheus and the prototype of → Beta Cephei variables. It is a variable B2 type → giant star with a visual magnitude of 3.23 varying with a period of 4.57 hours. Its mass is a dozen times that of the Sun. Beta Cephei is a → triple system lying at a distance of about 600 → light-years. The inner → spectroscopic companion, → spectral type A, is only about 45 AU away, and takes around 90 years to orbit. The third visual companion is at least 2400 AU away, with an orbital period of at least 30,000 years.

Beta (β), the second letter of the Gk. alphabet; → Cepheus.

A variable star, of early B or late O types, undergoing radial pulsations with short periods (< 1 day). Beta Cephei stars are confined within a narrow band of the → H-R diagram above the upper → main sequence. They are believed to be near the end of core hydrogen-burning stars of approximately 10 to 20 solar masses. The famous bright stars → Spica and → Mirzam belong to this family.

→ Beta Cephei; → variable.

The transformation of a → radioactive nuclide in which a → beta particle is emitted. In beta minus decay, a → neutron changes into a → proton, → antineutrino, and → electron: n → p + e + ν^-. Beta plus decay involves the conversion of a proton to a neutron, → positron, and → neutrino: p → n + e⁺ + ν.

Beta (β), from → beta particle; → decay.