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

The illumination of the dark part of the Moon's disk by the light reflected from the Earth's surface and atmosphere. Also called → earthshine.

→ earth; → light.

The theory describing light as a wave phenomenon resulting from the combination of two electric and magnetic fields vibrating transversely and mutually at right angles. → electromagnetic radiation; → electromagnetic wave; → Maxwell's equations.

→ electromagnetic; → theory; → light.

Light exhibiting → elliptical polarization.

→ elliptic; → polarized; → light.

An intellectual movement in Europe during the 17th and 18th centuries celebrating human reason and scientific thought as the instruments of progress and subjecting conventional ways of thinking to rigorous critique. The Enlightenment culminated with the writings of Jean-Jacques Rousseau (1712-1778) and the Encyclopédistes, the philosophy of Immanuel Kant (1724-1804), and the political ideals of the French and American Revolutions, while the precursor in science and philosophy included Francis Bacon (1561-1626), René Descartes (1596-1650), Isaac Newton (1643-1727), John Locke (1632-1704), and Thomas Hobbes (1588-1679).

From enlighten, from en- + → light + -en + → -ment.

Asr, → age; rowšangari, noun from rowšangar "enlightener," from rowšan "light, bright, luminous, splendid," cognate with L. lux, → bright, + -gar a suffix of agent nouns, → -or.

The integrated intensity of all of the light emitted throughout the history of the Universe across the whole of the → electromagnetic spectrum, including those which are not individually detected. The EBL spectrum includes cosmological backgrounds associated with either primordial phenomena, such as the → cosmic microwave background radiation (CMBR), or photons emitted by stars, galaxies and → active galactic nuclei (AGN) due to → nucleosynthesis or other → radiative processes, including → dust scattering, → absorption and reradiation. The EBL may also contain signals that are diffuse and extended, including high-energy photons associated with dark matter particle decays or annihilation.

→ extragalactic; → background; → light.

The first astronomical observation done with a major newly built telescope.

→ first; → light.

The act, manner, or power of flying.

O.E. flyht "a flying, flight," from P.Gmc. *flukhtiz (cf. Ger. Flucht).

Parvâz, from Mid.Pers. parwâz; Av. pāirivāza- "overrunning," from pāiri- "over (of space), from" + vāza- from vaz- "to fly, float; to drive;" cf. Skt. vah-, vahati. Also Mid.Pers. vâz "jump, flight," Mod.Pers. Lori, Gilaki, Tabari vâz "jump, leap."

The set of all points in a → space-time diagram that are reached by signals travelling from a specified point at the speed of light.

→ future; → light; → cone.

1) That portion of → electromagnetic radiation visible to the human → eye. However, other bands of the → electromagnetic spectrum are also often referred to as different forms of light.
2) Of little weight; not heavy.

1) O.E. leoht, leht, from W.Gmc. *leukhtam (cf. O.Fris. liacht, M.Du. lucht, Ger. Licht), from PIE *leuk- "light, brightness," cognate with Pers. rowšan "bright, clear," ruz "day," rowzan "window, aperture;" foruq "light," and afruxtan "to light, kindle;" Mid.Pers. rôšn "light; bright, luminous," rôc "day;" O.Pers. raucah-rocânak "window;" O.Pers. raocah- "light, luminous; daylight;" Av. raocana- "bright, shining, radiant;" akin to Skt. rocaná- "bright, shining," roka- "brightness, light;" Gk. leukos "white, clear;" L. lux "light" (also lumen, luna); Fr. lumière.
2) From O.E. leoht, from P.Gmc. *lingkhtaz (cf. O.N. lettr, Swed. lätt, O.Fris., M.Du. licht, Ger. leicht, Goth. leihts), from PIE base *le(n)gwh- "easy, agile, nimble."

1) Nur, from Ar.
Luž "light," in Sangesari (luženg variant of rowzan "vent, window"), variant of Pers. ruz "→ day," cognate with light, as above.
2) Sabok, from Mid.Pers. sapuk "light, brisk;" from O.Pers. *θapu-ka-, from Proto-Iranian *θrapu-ka-, from PIE *trep- "to shake, tremble;" cf. Gk. trepein "to turn;" L. trepidus "agitated, anxious;" Skt. trepa- "hasty."

The reflex adaptation of the eye to bright light, consisting of an increase in the number of functioning cones, accompanied by a decrease in the number of functioning rods; opposed to dark adaptation.

→ light; → adaptation.

A bright, confusing, and excessive grouping of light sources. Light clutter is a type of → light pollution. It is a general term relating to lights put up everywhere, without regard to what their purpose really is.

→ light; → clutter.

The set of all directions in which a light signal can travel toward an event (past light cone) or from an event (future light cone).

→ light; → cone.

1) A curve showing the behavior of the light from a → variable star over a period of time.
2) → supernova light curve.

→ light; → curve.

A cylinder of radius cP/(2π) around a → pulsar's spin axis, where P is the pulsar period and c the → speed of light. At this surface, the velocity of a hypothetical object that corotates with the → neutron star would reach the speed of light.

→ light; → cylinder.

The deviation of a light ray by the gravitational field of a massive body. For example, stellar light passing near the Sun will be deviated by 1''.75 at the Sun's limb.

→ light; → deflection.

Reflection of light from a stellar outburst by successively more distant clouds of dust surrounding the star. For example, the light echoes from two shells of dust near supernova 1987A, or those of star V838 Mon.

→ light; → echo.

In astrophysics, a chemical element that has an atomic number of one, two, or three, such as hydrogen, helium, and lithium; sometimes also beryllium and boron.

→ light; → element.

An atmospheric optical phenomenon appearing as a vertical shaft of light extending from the Sun or other bright light source during very cold weather. Light pillars or → sun pillars occur when artificial light or sunlight near the horizon is reflected from falling ice crystals associated with thin, high-level clouds. The ice crystals have a hexagonal plate shape and fall with a horizontal orientation, gently rocking from side to side as they fall.

→ light; → pillar.

The inappropriate or excessive use of artificial light. It brightens the sky and has a particularly damaging effect on astronomical observations. More generally, light pollution can have serious environmental consequences for humans, wildlife, and our climate. Types of light pollution include: → glare, → skyglow, → light trespass, and → light clutter.

→ light; → pollution.

An imaginary line directed along the path that the light follows. In other words, light pictured simply in terms of straight lines.

→ light; → ray.