An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The → locus of the intersection of input and output → conjugate rays in an optical system satisfying the → Abbe sine condition.

→ Abbe sine condition; → sphere.

An ancient instrument, used since ancient times until the Middle ages and later, to determine positions of celestial bodies. It consisted of an assemblage of rings, all circles of the same sphere, designed to represent the positions of the important circles of the celestial sphere.

L. armillarius, from armilla "arm ring, bracelet," from armus "arm" + → sphere.

Zâtolhelaq from Ar. "multi-ringed," from zât "holder, keeper" + helaq "rings," from halqah "ring."

A layer of soft, partly molten, rock in the → Earth's mantle, located at a depth of 100 to 250 km, over which the more rigid plates of the → lithosphere are in motion.

Asthenosphere, from Gk. asthenes "weak" + → sphere.

Sostsepehr, from sost "weak, tender" + sepehr, → sphere.

1) The gaseous envelope surrounding a star, planet, or moon. Several solar system planets retain considerable atmospheres, due to their strong gravitational force. The gas motions in the planetary atmosphere, as a response to the heating, coupled with the rotation forces, generate the meteorological systems. The planetary satellites → Titan and → Triton also have atmospheres (M.S.: SDE).
2) A unit of pressure, called standard atmosphere, which is the pressure of air balanced by a column of mercury 76 cm high with a density of the mercury of 13.595 g/cm³ at normal acceleration of gravity. Such a column applies a pressure equal to its weight to each square cm, or 1.01325 x 10⁶ dynes/cm² = 1.01325 x 10⁵ N/m². Since this pressure is equal to 1.03323 kilograms of force per square centimeter, instead of it use is often made of the technical atmosphere (at), exactly equal to 1 kgf/cm².

New L. atmosphaera, from Gk. atmos "vapor" + spharia "sphere."

Havâsepehr, from Mod.Pers. havâ, → air, + sepehr, → sphere. Javv "air, atmosphere," from Ar. jauw.

The part of a planet or moon within which life can occur. It may include the crust, oceans, and atmosphere.

Biosphere, from → bio- + → sphere.

Zistsepehr, from zizt-, → bio-, + sepehr→ sphere.

The → blackbody surface of the → Universe defined at a → redshift of about z ≥ 2 × 10⁶. This is distinct from the → last scattering surface, in other words the → cosmic microwave background radiation (CMBR), which refers to z = 1100. Prior to the epoch of the blackbody photosphere the distortions from the → Big Bang are exponentially suppressed.

→ blackbody; → atmosphere.

A sphere of interstellar gas at uniform temperature in equilibrium under its own gravitation and an external pressure. The pressure of a hotter surrounding medium causes the sphere to collapse. → Bonnor-Ebert mass.

→ Bonnor-Ebert mass; → sphere.

A piece of glass of roundish shape, possibly made of rock crystals or a globular container filled with water, whose use is attested in ancient civilizations. In his comedy The Clouds, the Greek playwright Aristophanes (448-380 BC) mentions globules of glass that were known as burning spheres. Several Roman writers (Pliny, Seneca, Plutarch) speak of burning glasses. In particular, Seneca specifies that small and indistinct written characters appear larger and clearer when viewed through a globular glass filled with water. See also → magnifying glass.

→ burning; → sphere.

Guy, → globe; suzân "burning," → burning.

An imaginary sphere, of large but indefinite dimension, used as a basis to define the position coordinates of celestial bodies. The center can be the Earth, the observer, or any other point which plays the role of origin for a given system of coordinates. Seen from the Earth, the celestial sphere rotates around the → celestial axis every 23h 56m 04s (the → sidereal day), as a result of the Earth's rotation. Two important circles on the celestial sphere are the → celestial equator and the → ecliptic. The angle between them, about 23.40 degrees, is known as the → obliquity of the ecliptic. The celestial equator and the ecliptic intersect at two points, → vernal equinox and → autumnal equinox. The positions of the → celestial poles and therefore that of the → celestial equator move gradually on the celestial sphere, due to → precession.

→ celestial; → sphere.

A region of the stellar atmosphere situated above its → photosphere. The Sun's chromosphere extends from the about 500 km above the photosphere basis, up to 9,000 km, where it meets the → corona. For a plane-parallel model, the chromosphere is more or less continuous throughout the first 1,500 km, but breaks into indented spicules beyond that height. The chromosphere temperature grows from 4,400 K at 500 km to almost 6,000 K at 1,000-2,000 km. A rapid growth of coronal temperatures is registered at heights of about 2,500 km (the transition region), the exact height depending on the local magnetic field intensity. Actually, the chromosphere is made of rising and, often, falling jets called → spicules, which go up to 15,000 km. In the uppermost part of the chromosphere the density is the millionth part of its density at the base. Immediately before or after a solar → total eclipse, the chromosphere becomes visible either as a crescent or as a red → diamond ring, due to → H-alpha emission, from which it also gets its name. Moreover, the chromosphere can be seen in → H and K lines of calcium during eclipses, and in ultraviolet emission lines from space. The presence of the chromosphere around cold → dwarf stars is deduced from similar emissions (M.S.: SDE).

→ chromo- "color," because of the reddish-pink color of the chromosphere which is seen around the Sun during a total eclipse and is due to the dominance of the → H-alpha line; → sphere.

A sphere containing a polyhedron (such as a pyramid) all of whose vertices lie on the surface of the sphere. The polyhedron so contained is said to be inscribed in the sphere.

Circumscribed p.p. of → circumscribe; → sphere.

The envelope of → gas and → dust around a → comet nucleus, also known as → coma. As the comet approaches the → Sun, the frozen materials → sublimate and give rise to an expanding atmosphere. The atmosphere is composed of dust, → molecules, → radicals, and molecular → ions released from the inner coma with velocities ~ 0.5 to 1 km s^-1, well above the → escape velocity for the nucleus. The → chemical species observed in cometary spectra can be divided into several categories: (i) atoms and molecules related to → water (H, O, OH, OH⁺, H2O, H2O⁺), (ii) carbon and related molecules (C, C⁺, CO, CO⁺, CO₂⁺, C₂, CH, CH⁺, HCO, H₂CO), (iii) → nitrogen and related molecules (CN, CN⁺, HCN, CH₃CN, NH, NH₂, N₂⁺, NH₃, NH₄), (iv) → sulphur and related molecules (S, CS, S₂, H₂S⁺), (v) → metals (Na, K, Ca, Co, Cr, Cu, V, Fe, Mn, Ni). For a typical average comet the neutral atmosphere is first seen when the heliocentric distance is d ≤ 3 → astronomical units.

→ cometary; → atmosphere.

A hypothetical structure built around a → star by an advanced → civilization to utilize most or all of the → energy radiated by their star. The idea of such a sphere was first formalized and popularized by theoretical physicist Freeman Dyson in 1960, though it was originally put forward by a 1945 science fiction novel. Dyson assumed that the power needs of → intelligent civilizations never stops increasing. He also proposed that searching for the existence of such structures might lead to the discovery of advanced civilizations elsewhere in the Galaxy. Sometimes referred to as a → Dyson shell or → megastructure.

Freeman John Dyson (1923-). His article, entitled "Search for Artificial Stellar Sources of Infrared Radiation," appeared in the 1960 issue of Science, 131 (3414), 1667-1668; → sphere.

The space around a star in which a planet would experience external conditions that are not incompatible with the existence of life.

Ecosphere, from eco-, → ecology, + → sphere.

Bumsepehr, from bum "eco-," → ecology, + sepehr, → sphere.

The region between the → event horizon and the → stationary limit of a rotating → Kerr black hole. It is possible for a particle falling inside the ergosphere to break into two parts, one of which will fall into the black hole and the other will come out.

→ erg + → sphere.

→ spheres of Eudoxus.

→ spheres of Eudoxus.

1) The outermost portion of the Earth's → atmosphere. Extremely tenuous, it lies above the → ionosphere from a height of about 500 km, to the edge of → interplanetary space.
2) An extremely tenuous kind of atmosphere surrounding a → solar system body. Since the → mean free path is much greater than the atmospheric scale height. The → atoms or → molecules never collide with each other. → lunar exosphere.

→ exo- + → sphere.

That part of the atmosphere where the effects of the ground on the → turbulence conditions are negligible.

→ free, → atmosphere.

A simplifying assumption in the models of stellar atmosphere, according to which the absorption coefficient has the same value at all wavelengths.

→ gray; → atmosphere.

The vast, three-dimensional region of space around the Sun filled with the → solar wind and the remnant of the → solar magnetic field carried in it. It is bounded by the → heliopause, which is estimated to be 100 → astronomical units or more from the Sun. The radius of the heliosphere is expected to vary with the → solar cycle. The heliosphere may be very elongated owing to the presence of an interstellar wind of neutral hydrogen flowing from the direction of the Galactic center.

From → helio- + → sphere.