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

The apparent slow motion of the → radiant of a → meteor shower from night to night against the background stars due to the Earth moving in its orbit around the Sun.

→ radiant; → drift.

The energy that is transmitted in the form of → radiation, in particular as → electromagnetic radiation.

→ radiant; → energy.

Rate of flow of energy as → radiation.

→ radiant; → flux.

A measure of the amount of radiation emitted from a point expressed as the radiant flux per unit solid angle leaving this source.

→ radiant; → intensity.

To send out → energy, such as → heat or → light, in the form of → rays or → waves.

From L. radiat(us), p.p. of radiare "to shine, to beam" + -ate verbal suffix.

Tâbidan, variants tâftan "to shine," tafsidan "to become hot;" Mid.Pers. tâftan "to heat, burn, shine;" taftan "to become hot;" Parthian t'b "to shine;" Av. tāp-, taf- "to warm up, heat," tafsat "became hot," tāpaiieiti "to create warmth;" cf. Skt. tap- "to heat, be/become hot; to spoil, injure, damage; to suffer," tapati "burns;" L. tepere "to be warm," tepidus "warm;" PIE base *tep- "to be warm."

The emission of any → rays, → waves, or → particles from a source; usually applied to the → emission of → electromagnetic energy.

Verbal noun of → radiate.

A ring-shaped region in the → magnetosphere of a planet in which charged particles are trapped by the planet's magnetic field. The radiation belts surrounding Earth are known as the → Van Allen belts.

→ radiation; → belt.

Same as → radiation density constant.

→ radiation; → constant.

Damping of a system which loses energy by → electromagnetic radiation.

→ radiation; → damping.

The constant related to the total energy radiated by a → blackbody and defined as: a = 4σ/c, where σ is the → Stefan-Boltzmann constant and c the → speed of light. Its value is a = 7.5657 x 10^-15 erg cm^-3 K^-4. Same as → radiation constant.

→ radiation; → density; → constant.

The epoch in the history of the Universe, lasting from the → Big Bang until about 400,000 years later, when the temperature had dropped to 10⁹ K and the rate of electron-positron → pair annihilation exceeded the rate of their production, leaving radiation the dominant constituent of the Universe. The radiation era was followed by the → matter era.

→ radiation; → era.

1) The portion of an → electromagnetic field outside the → induction field where there is a power flow of both → magnetic and → electric components in a well-defined relationship.
2) → interstellar radiation field

→ radiation; → field.

The mean distance traveled by a photon or particle in a given medium before its energy is reduced by a factor e due to its interaction with matter.

→ radiation; → length.

Same as → antenna pattern.

→ radiation; → pattern.

The → momentum carried by → photons to a surface exposed to → electromagnetic radiation. Stellar radiation pressure on big and massive objects is insignificant, but it has considerable effects on → gas and → dust particles. Radiation pressure is particularly important for → massive stars. See, for example, → Eddington limit, → radiation-driven wind , and → radiation-driven implosion. The → solar radiation pressure is also at the origin of various physical phenomena, e.g. → gas tails in → comets and → Poynting-Robertson effect.

→ radiation; → pressure.

An illness resulting from excessive exposure to ionizing radiation. The earliest symptoms are nausea, vomiting, and diarrhea, which may be followed by loss of hair, hemorrhage, inflammation of the mouth and throat, and general loss of energy.

→ radiation; sickness, M.E. siknesse, seknesse; O.E. sēocnesse, from seoc + suffix -ness.

Bimâri "sickness, infirmity, disease," from bimâr "sick, infirm, afflicted;" Mid.Pers. vêmâr "sick, ill;" maybe by corruption of Proto-Iranian *amavayā-bara- "bearing illness;" cf. Av. amavayā- "pain, suffering, affliction;" Skt. ámīvā- "pain, grief, distress" + *bara- "bearing;" cf. Av. bar- "to bear, carry;" Mod.Pers. bar-, bordan "to bear, carry, lead." Alternatively, from *vi-mar-, prefixed *mar- "to die;" cf. Av. mar- "to die;" Mod.Pers. mir-, mordan "to die;" Skt. mar- "to die;" cognate with Gk. emorten "died;" L. morior "to die;" tâbeši related to tâbeš, → radiation.

The components of radiation arranged in order of their wavelengths, frequencies, or quantum energies. For particle radiation they are arranged in order of their kinetic energies.

→ radiation; → spectrum.

The temperature of a source calculated assuming that it behaves as a → blackbody that radiates with the same intensity at the same frequency. Compared to the → effective temperature, the radiation temperature is measured over a narrow region of the → electromagnetic spectrum.

→ radiation; → temperature.

→ radiative transfer.

→ radiation; → transfer.

→ radiative transfer equation.

→ radiation; → transfer; → equation.