local standard of rest
estânde-ye mahali-ye âram
Fr.: standard local de repos
A frame of reference that turns around the Galactic center at a velocity and a distance which are the mean values for the stars in the solar neighborhood. In this reference system the stars belonging to the solar neighborhood are statistically at rest. The orbital velocity of the Local Standard of Rest around the Galaxy is about 220 km/sec.
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."
havâsepehr-e estândé (#), javv-e ~ (#)
Fr.: atmosphère standard
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.
Fr.: chandelle standard
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.
Fr.: cosmologie standard
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.
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.
Fr.: époque de référence
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.
Fr.: erreur type
Same as → standard deviation.
model-e estândé, tarzâl-e ~
Fr.: modèle standard
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 of particle physics
model-e estânde-ye fizik-e zarre-yi
Fr.: modèle standard de la physique des particules
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.
Fr.: étoiles standard
Stars for which accurate color indices and/or magnitudes exist, defining a standard system.
Fr.: système standard
Photometric system used as a reference.
standard temperature and pressure (STP)
damâ o fešâr-e estândé
Fr.: conditions normales de température et de pression
1) The most commonly used definition is temperature of 273.15 K (0 °C) and
pressure of 1 → atmosphere.
→ standard; → temperature; → pressure.
Fr.: temps standard
The time in any of the 24 internationally agreed time zones into which the Earth's surface is divided. The primary zone is centered on the Greenwich meridian (0° longitude).
Fr.: valeurs standard
Photometric values of selected stars in a standard system.