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

The time interval between the release of an electron at the photocathode and the arrival of an electron at the anode. Transit time is not a single-valued quantity, but has a bell-shaped distribution.

→ transit; → time.

A → NASA space telescope devoted to the hunt for planets orbiting the brightest stars in the sky, launched on April 18, 2018. The mission is planned to monitor at least 200,000 stars for signs of → exoplanets using the → planetary transit method. TESS is equipped with four identical refractive → cameras with a combined → field of view (FOV) of 24 × 96 degrees. Each camera consists of a → CCD detector assembly, a → lens assembly, and a lens hood. The → entrance pupil diameter is 10.5 cm and the wavelength range 600 to 1,000 nm. The satellite is a follow-up of NASA's → Kepler spacecraft, but focuses on stars that are 30 to 100 times brighter than those Kepler examined.

→ transit; → exoplanet; → survey.

A planet that passes in front of its star directly between Earth and the star. The → transit method is used for detecting → exoplanets around stars.

→ transit; → planet.

A Belgian facility devoted to the detection and characterization of → exoplanets and to the study of → comets (→ transiting planet) and other → small solar system bodies. It consists of two 60 cm robotic telescopes located at the → European Southern Observatory, → La Silla, in Chile and at Oukaïmden Observatory in Marroco.

→ transit; → planet; → planetesimal; → small; → telescope.

1) Passage from one position, state, stage, subject, concept, etc., to another.
2) A change between phases such as solid to liquid or liquid to gas.
3) A change in the → energy level or state of an atom or nucleus. → atomic transition, → bound-bound transition, → bound-free transition, → cascade transition, → discrete transition, → forbidden transition, → hyperfine transition, → nuclear transition, → permitted transition, → phase transition, → quark-hadron phase transition, → radiative transition, → rotational transition, → semi-forbidden transition, → transition disk, → transition function, → transition probability, → vibrational transition.

From L. transitionem (nominative transition) "a going across or over," noun of action from transire "go or cross over," from → trans- "across" + ire "to go."

Gozareš, verbal noun of gozaštan "to transit, pass," → transit, + -eš, → -tion.

The → accretion disk of a → T Tauri star that displays very weak or no → infrared excess at → near infrared wavelengths, but shows strong excess at → intermediate infrared and longer wavelengths. This happens when the hot inner dust disk has dissipated whereas the cooler outer disk is still intact.

→ transition; → disk.

The → probability of finding the → Universe in a → state labelled X₂ at a time t₂, if it was in a state X₁ at an earlier time t₁.

→ transition; → function.

The probability that a quantum-mechanical system will make a transition from a given initial state to a given final state.

→ transition; → probability.

In fluid mechanics, a flow composed of → laminar and → turbulent flows, for which the → Reynolds number is between 2300 and 4000.

→ transition; → flow.

Math.: A permutation of a set of elements that interchanges two elements and leaves the remaining elements in their original positions. For example, the swapping of 2 and 5 to take the list 123456 to 153426 is a transposition.
Optics: The changing of the relative curves of a lens without changing its refractive value.

→ trans-; → position.

The coordinates of an object for a given date, with respect to the true equator and the true equinoxes for the instant of time in question.

→ true; → position.

An institution of higher education composed of several faculties for teaching and research and authorized to grant academic degrees.

M.E., from O.Fr. universitei, from M.L. universitatem (nominative. universitas), in L.L. "corporation, society," from L., "the whole, aggregate," from universus "whole, entire," → universe.

Dânešgâh, from dâneš, → science, + -gâh "place; time" (Mid.Pers. gâh, gâs "time;" O.Pers. gāθu-; Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come").

The movement of a celestial body across a celestial meridian's upper branch. Same as → upper culmination.

→ upper; → transit.

A → tensor density of → order 1.

→ vector; → density.

A transition between two → quantized  → levels of a → molecule that have different vibrational energies.

→ vibrational; → transition.

A slight change in the → energy level of a → molecule due to → vibrational transition and/or → rotational transition.

→ vibrational; → rotational; → transition.

The property of a → fluid that resists the force tending to cause the fluid to flow. Viscosity may be thought of as the internal → friction of two fluid layers which flow parallel to each other at different speeds. The cause of viscosity is the transport of → momentum by the molecules from one layer to the other. Viscosity is given by η = φ.u.λ.ρ, where φ is a coefficient which depends on the nature of the interaction between the molecules, u is the average velocity of thermal motion of the molecules, λ is the → mean free path, and ρ the → density of the fluid. Also called → dynamic viscosity or → absolute viscosity. See also → kinematic viscosity.

Noun from → viscous; → -ity.

A constant the value of which is characteristic for any given → tensor density.

→ weight; → tensor; → density.

The final kinetic energy of the → stellar wind expressed by: (1/2)Mdot.v_∞² = (1/2)(v_∞/c)L For an O6 star, L ~ 3 x 10⁵Lsun and v_∞ ~ 2000 km s^-1, which give a wind luminosity of ~ 1 x 10³⁷ erg s^-1, about 1% of the → stellar luminosity. See also → photon tiring limit.

→ wind; → luminosity.