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.
Fr.: problème de Kepler
1) Given the trajectory of a particle moving in a → central force
field, determine the
law governing the central force.
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 deg2 (about 12° diameter). The expected mission lifetime is 3.5 years extendible to at least 6 years.
In honor of Johannes → Kepler; → spacecraft.
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).
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).
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: P2∝ a3 (year 1618). More accurately, P2 = (4π2a3) / [G(M1 + M2)], where M1 and M2 are the masses of the two orbiting objects in → solar masses and G is the → gravitational constant. In our solar system M1 = 1. The → semi-major axis size (a is expressed in → astronomical units and the period (P) is measured in years.
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: ΩK = (GM/r3)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.
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.
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.
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).
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.