a- (#), an- (#); bi- (#); nâ- (#)
Prefix same as → a- "not, without" occurring before a vowel or h in loanwords from Greek.
Fr.: théorie de Jordan-Brans-Dicke
A relativistic theory of gravitation which involves a → scalar field in addition to the → metric (→ tensor field) used in rarr; general relativity. It obeys the → equivalence principle, but tries at the same time to comply with → Mach's principle owing to possible spatial and temporal variations of the → gravitational constant, which is inversely proportional to the scalar field. The theory uses a new dimensionless parameter to determine the discrepancy between its predictions and those of general relativity. So far there is no firm indication of its validity. Same as → scalar-tensor theory.
Named after the creators, Carl Brans (1935-) and Robert Dicke (1916-1997), who presented the theory in 1961, based on the initial work of Pascual Jordan (1902-1980); → theory.
Fr.: photon de Lyman-Werner
An → ultraviolet photon with an energy between 11.2 and 13.6 eV, corresponding to the energy range in which the Lyman and Werner absorption bands of → molecular hydrogen (H2) are found (→ Lyman band, → Werner band). The first generation of stars produces a background of Lyman-Werner radiation which can → photodissociate molecular hydrogen, the key → cooling agent in metal free gas below 104 K. In doing so, the Lyman-Werner radiation field delays the collapse of gaseous clouds, and thus star formation. After more massive → dark matter clouds are assembled, atomic line cooling becomes effective and H2 can begin to shield itself from Lyman-Werner radiation.
→ Lyman; → Werner band; → photon.
radebandi-ye Morgan-Keenan (#)
Fr.: classification de Morgan-Keenan
A system of → spectral classification introduced in 1943 by William W. Morgan (1906-1994), Philip C. Keenan (1908-2000), and Edith M. Kellman (1911-2007) at Yerkes Observatory. Also known as the MK (or MKK) classification or the → Yerkes system.
Named after the two main astronomers, as above; → classification.
pân- (#), sarâsar- (#), hamé- (#)
A prefix meaning "all, whole," used as a general formative (panorama; pantelegraph; pantheism; pantonality), and especially in terms implying the union of all branches of a group (Pan-Christian; Pan-Hellenic; Pan-Slavism).
From Gk. pan-, combining form of pas (neuter pan) "all, every," of unknown origin.
Pân- loan from Gk., as above.
A system for wide-field astronomical imaging developed and operated by the Institute for Astronomy at the University of Hawaii. Its goal is to survey the sky for moving or variable objects on a continual basis, and also produce accurate astrometry and photometry of already detected objects. It is situated at Haleakala Observatories near the summit of Haleakala in Hawaii. Pan-STARRS1 (PS1) was the first part of Pan-STARRS. The survey used a 1.8 meter telescope and a 1.4 Gigapixel camera to image the sky in five broadband filters (g, r, i, z, y). The PS1 consortium is made up of astronomers and engineers from 14 institutions and six countries. The survey was completed in April 2014. The Pan-STARRS Project is now focusing on building PS2.
Short for Panoramic Survey Telescope and Rapid Response System.
Variant of → plano-.
irang-e riše-ye câruši-ye miyângin, ~ ~ dovom-e ~
The square root of the second moment corresponding to the frequency function of a random variable.
arzeš-e riše-ye câruši-ye miyângin
Fr.: écart quadratique moyen, écart type
Statistics: The square root of the arithmetic mean of the squares of the deviation of observed values from their arithmetic mean.
Fr.: constante de Stefan-Boltzmann
The constant of proportionality present in the → Stefan-Boltzmann law. It is equal to σ = 5.670 × 10-8 W m-2 K-4 or 5.670 × 10-5 erg cm-2 s-1 K-4.
→ Stefan-Boltzmann law; → constant.
Fr.: loi de Stefan-Boltzmann
The flux of radiation from a blackbody is proportional to the fourth power of its absolute temperature: L = 4πR2σT4. Also known as Stefan's law.
Ludwig Eduard Boltzmann (1844-1906), an Austrian physicist, who made important contributions in the fields of statistical mechanics and statistical thermodynamics and Josef Stefan (1835-1893), an Austrian physicist; → law.