Fr.: luminosité absolue
A star's → intrinsic brightness, i.e. the total amount of energy radiated by the star per second. → Luminosity is often expressed in units of watts or erg/sec. The Sun's absolute luminosity is 3.86 × 1033 erg/sec.
Fr.: viscosité absolue
Airy transit circle
parhun-e nimruzâni-ye Airy
Fr.: circle méridien d'Airy
A → transit circle that defines the position of the → Greenwich Meridian since the first observation was taken with it in 1851. Airy's transit circle lies at longitude 0°, by definition, and latitude 51° 28' 38'' N.
Named after Sir George Biddell Airy (1801-1892), Astronomer Royal, at the Royal Observatory in Greenwich from 1835 to 1881. Airy transformed the observatory, installing some of the most advanced astronomical apparatus of his day and expanded both staff numbers and their workload; → transit; → circle.
anomalous luminosity effect
oskar-e tâbandegi-ye nâsân
Fr.: effet luminosité anormale
Discrepant luminosity classes derived for the same → Am star when different criteria are used. Lore specifically, a luminosity criterion may indicate a → giant star, wheras another criterion indicates a → supergiant.
naheš-e padidâr, jâ-ye ~
Fr.: position apparente
1) The position on the celestial sphere at which a heavenly body
would be seen from the Earth at a particular time.
sit-e axtaršenâsik, ~ axtaršenâxti
Fr.: site astronomique
A certain place whose characteristics, as to location, altitude, atmospheric conditions, etc., make it appropriate for astronomical observations.
Fr.: proposition atomique
Fr.: transition atomique
tâbandegi-ye tâvsanji, ~ tâvsanjik
Fr.: luminosité bolométrique
The total rate of energy output of an object integrated over all wavelengths.
Fr.: transition liée-liée
Fr.: transition liée-libre
Fr.: luminosité de coupure
A characteristic luminosity around which the → luminosity function of a sample of galaxies changes to a steeper slope or exponentially declines.
Fr.: transition en cascade
A photon generation mechanism in an atom in which a transition initiates a series of secondary transitions from lower electronic levels.
Fr.: position catalogue
Same as catalog place and → mean catalog place.
Fr.: proposition catégorique
In a → syllogism, a → proposition or statement that deals with inclusion or exclusion of members of → subject classes in → predicate classes. Categorical propositions are of four basic forms, see → Aristotelian form.
Fr.: densité de charge
The → electric charge per unit volume in space, or per unit area on a surface, or per unit length of a line. They are respectively called volume- (ρ), surface- (σ), or line (λ) charge density.
Fr.: composition chimique
coefficient of viscosity
Fr.: coefficient de viscosité
A quantity that indicates a property of fluids and is defined by the ratio of shearing → stress to the rate of change of shearing → strain. It is also simply called viscosity. The coefficient of viscosity is expressed by: μ = (F/A) / (dv/dy), where F is the force required to maintain a steady velocity difference dv between any two parallel layers of the fluid, A is the area of the layers, and dv/dy is the → velocity gradient between two points separated by a small distance measured at right angles to the direction of flow. The unit of viscosity is that of force times distance divided by area times velocity. Thus, in the cgs system, the unit is 1 dyne.cm/cm2.(cm/s), which reduces to 1 dyne.s/cm2. This unit is called 1 → poise.
Fr.: diagramme couleur-luminosité