An Etymological Dictionary of Astronomy and Astrophysics
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The → excitation temperature of the → hyperfine structure levels of the → neutral hydrogen→ 21-centimeter line.

→ spin; → temperature.

1) The most commonly used definition is temperature of 273.15 K (0 °C) and pressure of 1 → atmosphere.
2) Chemistry: Temperature of 273.15 K (0 °C) and pressure of 10⁵  → pascal (Pa)s (1 → bar). International Union of Pure and Applied Chemistry (IUPAC) recommends that the former use of the pressure of 1 atm as standard pressure (equivalent to 1.01325 × 10⁵ Pa) should be discontinued.

→ standard; → temperature; → pressure.

A condition in which there is an excess of the actual temperature gradient over the → adiabatic temperature gradient corresponding to the same pressure gradient. A region with superadiabatic temperature gradient is convectively unstable. → Hayashi forbidden zone.

→ super-; → adiabatic; → temperature; → gradient.

1) For a star, same as → effective temperature.
2) Meteo.: The air temperature at or near the earth's surface.

→ surface; → temperature.

A physical quantity characterizing the mean random motion of molecules in a physical body. In other words, a measure of the average kinetic energy of the particles of a system.

From L. temperatura "a tempering, moderation," from temperatus, p.p. of temperare "to moderate, to mix." Sense of "degree of heat or cold" first recorded 1670 (Boyle), from L. temperatura, used in this sense by Galileo.

Damâ, from dam "breath of an owen; bellows; smoke; air," also "moment, time," from Mid./Mod.Pers. damidan "to blow, breathe;" Av. dāδmainya- "blowing up;" cf. Skt. dahm- "to blow," dhámati "blows;" Gk. themeros "austere, dark-looking;" Lith. dumti "to blow;" PIE dhem-/dhemə- "to smoke, to blow."

Cosmology: Minute temperature variations of the cosmic microwave background radiation.

→ temperature; → anisotropy.

A physical quantity that describes the rate of change of temperature with displacement in a given direction from a given reference point. Same as → thermal gradient.

→ temperature; → gradient.

Meteo.: A reversal in the normal temperature decrease, the temperature rising with increased elevation in the atmosphere instead of falling. A layer in which temperature increases with altitude.

→ temperature; → inversion.

A temperature scale, measured in → kelvin (K), that is related to the energy possessed by matter; it was formerly known as → absolute temperature. The zero point on the scale (0 K) is absolute zero. Thermodynamic temperature can be converted to temperature on the → Celsius scale by subtracting 273.15.

→ thermodynamic; → temperature.

The mean temperature at which a gravitationally → bound system would satisfy the → virial theorem. For a system of mass M and radius R with constant density, the gravitational energy per unit mass is W = GM/R. The kinetic energy per unit mass is E = (3/2)kT_vir/μ, where k is → Boltzmann's constant and μ the mean molecular weight. According to the virial theorem, E = W/2, which leads to the virial temperature T_vir = (1/3)(GM/kR).

→ virial; → temperature.