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

Of a transiting → exoplanet, the event and the interval of time during which the planet passes in front of its host star. The planet occults a portion of the stellar disk, and a fraction of light from the star is seen after traversal through the atmosphere around the planet's limb. → secondary eclipse.

→ primary; → eclipse.

In a → reflecting telescope, the first mirror that collects the light and focuses it to the → focal plane.

→ primary; → mirror.

The main rainbow that forms between about 40° and 42° from the → antisolar point (or about 50° from the → antisolar point), as viewed by the observer. The light path involves → refraction and a → single  → reflection inside the water → droplet. If the drops are large, 1 millimeter or more in diameter, red, green, and violet are bright but there is little blue.

As the droplets get smaller, red weakens.

Rainbows are not seen in midday since the whole 42° circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the Sun is illuminating from the west.

→ primary; → rainbow.

In a → multiple star system, the most massive → component. In other words, the star nearest to the system's → center of garvity.

→ primary; → star .

A person who institutes or conducts legal proceedings, especially in a criminal court.

M.L. prosecutor, agent noun from prosequi "follow after, accompany; chase, pursue;" from → pro- "forward" + sequi "to follow," → sequence.

Dâsetân, literally "justice obtainer," from dâd, → justice, + setân agent noun of setândan "to obtain, to take," from Mid.Pers. statan "to take, seize;" Av. (+ *fra-) frastan- "to take, convey forward;" Proto-Ir. *staHn- "to take;" cf. L. prae-stināre "to buy, fix a price" (Cheung 2007).

1) A problem that cannot be easily or readily solved.
2) A game, question, or problem designed for testing ingenuity.

Of unknown origin.

Cistân from cist "what is?," + -ân noun suffix.

1) An institution where instruction is given, especially to persons under college age.
2) An institution for instruction in a particular skill or field.
3) A college or university (Dictionary.com).

M.E. scole, O.E. scôl, from L. schola, from Gk. scholé "spare time, leisure," from skhein "to get."

Dabestân, from Mid.Pers. dibistân "school," literally "place of writing" or "the place where documents are kept," from dib, dip "→ document," + -istân suffix of place, → summer.

Either of the two points on the → ecliptic at which the apparent → longitude of the → Sun is 90° or 270°. Also the time at which the Sun is at either point. Solstices occur when the Earth's axis is oriented directly toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes. → summer solstice, → winter solstice.

M.E., from O.Fr. solstice, from L. solstitium "point at which the sun seems to stand still," from sol, → sun, cognate with Pers. xor, xoršid, hur, as below, + p.p. stem of sistere "to come to a stop, make stand still," akin to Pers. istâdan "to stand," as below.

Xoristân, is composed of two components. The first one xor "sun," variant hur; Mid.Pers. xwar "sun;" Av. hū-, hvar- "sun;" cf. Skt. surya-, Gk. helios, L. sol, cognate with E. sun, as above; PIE base *sawel- "sun." The second component istân "standing," from istâdan "to stand;" Mid.Pers. êstâtan; O.Pers./Av. sta- "to stand, stand still; set;" Av. hištaiti; cf. Skt. sthā- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" Goth. standan; PIE base *sta- "to stand."

The great circle of the celestial sphere which passes through the poles of the celestial equator and the solstice points. → equinoctial colure.

Solsticial, adj. of → solstice; → colure.

The two points of the ecliptic the most distant from the equator.

Solsticial, adj. of → solstice; → point.

Any set of conditions that describe the normal, desired, or ideal state of something, and that serves a basis for representing or evaluating actual examples of this thing.

M.E., from O.Fr. estandart "banner, standard," probably from Frankish *standord; cf. Ger. Standort "standing-point," from standan "to stand," cognate with Pers. istâdan, as below, with the second component conformed to -ard.

Estândé, literally "made stand, fixed," p.p. istândan transitive verb of istâdan, "to → stand."

A hypothetical vertical distribution of atmospheric temperature, pressure, and density that, by international agreement, is taken to be representative of the atmosphere for purposes of pressure altimeter calibrations, aircraft performance calculations, aircraft and missile design, ballistic tables, etc.

→ standard; → atmosphere.

An astronomical object, belonging to some class, that has a known luminosity. In principle, by comparing the known luminosity to the observed brightness, the distance to the object can be derived. The four major primary distance indicators are Cepheids, supernovae, novae, and RR Lyrae variables. The secondary distance indicators include H II regions, globular clusters, brightest red and blue stars. → primary calibrator; → secondary calibrator.

→ standard; → candle.

The conventional → Big Bang model, which is based on two assumptions: the → cosmological principle of homogeneity and isotropy leading to the → Robertson-Walker metric, and → Einstein's field equations of general relativity along with familiar properties of matter. This model is a remarkably successful operating hypothesis describing the evolution of the Universe from 1/100 second after the initial event through to the present day. It provides explanations for several basic problems such as: → Hubble's law of recession of galaxies, interpreted in terms of the expansion of the Universe; the abundances of the → light elements, in excellent agreement with the predictions of → primordial nucleosynthesis; and the thermal spectrum and angular isotropy of the → cosmic microwave background (CMB) radiation, as expected from a hot, dense early phase of expansion. For a non-standard model, see → ekpyrotic Universe.

→ standard; → cosmology.

The most widely used measure of dispersion of a frequency distribution. It is equal to the positive square root of the → variance. Same as → standard error. Not to be confused with the → root mean square error.

→ standard; → deviation.

A particular date and time that specifies the reference system to which celestial coordinates are referred. From 1984 the → Julian year is used, as denoted by the prefix J, e.g. J2000.0.

→ standard; → epoch.

Same as → standard deviation.

→ standard; → error.

The accepted but possibly incomplete theoretical framework which usually describes a set of phenomena. For example, the model that describes the origin of the Universe, or the model concerned with the processes in the interior of the Sun.

→ standard; → model.

The theory developed since the 1970s, which is based on the theories and discoveries since the 1930s, and aims at explaining the fundamental structure of matter. According to the standard model, everything in the universe is made from a few basic building blocks called fundamental particles, governed by four fundamental forces. The particles occur in two basic types, called quarks and leptons. Three of the four fundamental forces (except gravity) and their carrier particles are included in the Standard Model. The Standard Model has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena. Over time and through many experiments, the Standard Model has become established as a well-tested physics theory.

→ standard; → model; → particle; → physics.

Stars for which accurate color indices and/or magnitudes exist, defining a standard system.

→ standard; → star.