Kepler Kepler (#) Fr.: Kepler Johannes Kepler (1571-1630), a German mathematician and astronomer and a key figure in the 17th century astronomical revolution. He discovered that the Earth and planets travel about the Sun in elliptical orbits; gave three fundamental laws of planetary motion, and also did important work in optics and geometry. |
Kepler problem parâse-ye Kepler Fr.: problème de Kepler 1) Given the trajectory of a particle moving in a → central force
field, determine the
law governing the central force. |
Kepler spacecraft teleskop-e fazâyi-ye Kepler Fr.: télescope spatial de Kepler A → NASA space telescope launched in March 2009 to discover Earth-size planets using the → transit method. The telescope has a diameter of 0.95 m and its only instrument is a → photometer that continuously monitors the brightness of over 145,000 → main sequence stars in a fixed field of view of 115 deg^{2} (about 12° diameter). The expected mission lifetime is 3.5 years extendible to at least 6 years. In honor of Johannes → Kepler; → spacecraft. |
Kepler's equation hamugeš-e Kepler Fr.: équation de Kepler An equation that enables the position of a body in an elliptical orbit to be calculated at any given time from its orbital elements. It relates the → mean anomaly of the body to its → eccentric anomaly. |
Kepler's first law qânun-e naxost-e Kepler (#) Fr.: première loi de Kepler Planets move in elliptical paths, with the Sun at one focus of the ellipse (year 1609). |
Kepler's laws qânunhâ-ye Kepler (#) Fr.: lois de Kepler 1) The planets move about the Sun in ellipses, at one focus of which the Sun is situated. |
Kepler's second law qânun-e dovom-e Kepler (#) Fr.: deuxième loi de Kepler A line joining a planet to the Sun sweeps out equal areas in equal intervals of time (year 1609). |
Kepler's star setâre-ye Kepler (#) Fr.: étoile de Kepler A → supernova in → Ophiuchus, first observed on 1604 October 9, and described by Johannes Kepler in his book De stella nova (1606). It reached a maximum → apparent magnitude of -3 in late October. The star remained visible for almost a year. The → light curve is that of a → Type Ia supernova. The → supernova remnant consists of a few filaments and brighter knots at a distance of about 30,000 → light-years. It is the radio source 3C 358. Also known as SN 1604 and Kepler's supernova. |
Kepler's third law qânun-e sevom-e Kepler (#) Fr.: troisième loi de Kepler The ratio between the square of a planet's → orbital period (P) to the cube of the mean distance from the Sun (a) is the same for all planets: P^{2}∝ a^{3} (year 1618). More accurately, P^{2} = (4π^{2}a^{3}) / [G(M_{1} + M_{2})], where M_{1} and M_{2} are the masses of the two orbiting objects in → solar masses and G is the → gravitational constant. In our solar system M_{1} = 1. The → semi-major axis size (a is expressed in → astronomical units and the period (P) is measured in years. |
Keplerian Kepleri Fr.: keplerien Of or pertaining to Johannes Kepler or to his works or discoveries. From → Kepler + -ian a suffix forming adjectives. |
Keplerian angular velocity tondâ-ye zâviye-yi-ye Kepleri Fr.: vitesse angulaire keplérienne The angular velocity of a point in a circular orbit around a central mass. It is given by: Ω_{K} = (GM/r^{3})^{1/2}, where G is the → gravitational constant, M is the mass of the gravitating object, and r is the radius of the orbit of the point around the object. |
Keplerian disk gerde-ye Kepleri, disk-e ~ Fr.: disque keplérien A circumstellar disk (such as an → accretion disk or a → protoplanetary disk) in which the → angular velocity at each radius is equal to the angular velocity of a circular → Keplerian orbit at the same radius. The main characteristic of the Keplerian disk is that → orbital velocity varies as r^{-1/2}. This means that an object on an orbit closer to the central mass turns more rapidly than that on a farther orbit. This velocity difference is at the origin of internal friction or kinematic viscous forces between disk particles, which heats up the material. |
Keplerian orbit madâr-e Kepleri (#) Fr.: orbit keplérienne The orbit of a spherical object of a finite mass around another spherical object, also of finite mass, governed by their mutual → gravitational forces only. |
Keplerian orbital velocity tondâ-ye madâr-e Kepleri Fr.: vitesse d'orbite képlérienne The velocity of an object orbiting another object according to → Kepler's laws. |
Keplerian rotation curve xam-e carxeš-e Kepleri (#) Fr.: courbe de rotation keplérienne A → rotation curve in which the speed of the orbiting body is inversely proportional to the → square root of its distance from the mass concentrated at the center of the system. |
Keplerian shear karn-e Kepleri Fr.: cisaillement keplerien Shearing motion of an ensemble of particles, each on a nearly circular, → Keplerian orbit. → Orbital velocity decreases as orbital radius increases, yielding shear. Viscous drag on such shear, due to ring-particle collisions, plays a key role in ring processes (Ellis et al., 2007, Planetary Ring Systems, Springer). |
Keplerian telescope durbin-e Kepler, teleskop-e ~ (#) Fr.: télescope de Kepler A → refracting telescope which has simple → convex lenses for both → objective and → eyepiece. It suffers from → chromatic aberration, which can be reduced by increasing the → focal ratio. It was first devised by Kepler in 1615. |
Kerberos Kerberos Fr.: Kerberos The fourth → natural satellite of → Pluto discovered in 2011 using the → Hubble Space Telescope. Also called Pluto IV (P4). It has an estimated diameter of 14-44 km, which makes it the second smallest known moon of Pluto after → Styx. Kerberos revolves around Pluto in the region between → Nix and → Hydra at a distance of about 58,000 km and makes a complete orbit roughly every 32.1 days. Named after the three-headed dog of Greek mythology. |
kernel astel Fr.: noyau 1) Chemistry: The remainder of an atom after the valence electrons have
been removed. Kernel, from M.E. kirnel, from O.E. cyrnel, from P.Gmc. *kurnilo- (cf. M.H.G. kornel, M.Du. cornel), from *kernan- (root of corn "seed, grain"), akin to L. granium, + -el, diminutive suffix, variant of → -al. Astel, from asté "kernel, fruit stone," variants hasté, ostoxân "bone," from Mid.Pers. astak "fruit stone, bone," ast "bone;" Av. ast- "bone;" cf. Skt. asthi- "bone;" Gk. osteon; L. os; Hittite hashtai-; PIE base *os- + Pers. diminutive suffix -el→ -al. |
Kerr black hole siyah câl-e Kerr (#) Fr.: trou noir de Kerr A → black hole that possesses only mass (not electric charge) and rotates about a central axis. It has an → ergosphere and a → stationary limit. Named after the New Zealand mathematician Roy P. Kerr (1934-) who, in 1963, was the first to solve the → field equationss of Einstein's theory of → general relativity for a situation of this kind; → black hole. |