Fr.: fenêtres galactiques
The regions near the Galactic plane where there is low absorption of light by interstellar clouds so that some external galaxies may be seen through them.
sâl-e kahkešâni (#)
Fr.: année galactique
The time taken for the Sun to revolve once around the center of the Milky Way, amounting to about 220 million years.
ostacân bâ marpel-e kahkešâni
Fr.: flot à l'échelle galactique
The enormous amounts of → mass and → energy released from active galaxies into the → intergalactic medium. → Supermassive black holes, believed to exist at the centres of active galaxies (→ active galaxy), → accrete matter and liberate huge quantities of energy. The energy output is often observed as → active galactic nuclei (AGN) outflows in a wide variety of forms, e.g. → collimated → relativistic jets and/or huge overpressured cocoons in → radio, → blueshifted broad → absorption lines in the → ultraviolet and → optical, → warm absorbers and ultrafast outflows in → X-rays, and → molecular gas in → far infrared. Moreover, the processes of → star formation and → supernova explosions release mass/energy into the surroundings. This → stellar feedback heats up, ionizes and drives gas outward, often generating large-scale outflows/→ winds. Galactic outflows are observed at low redshifts reaching a velocity as large as 1000 km s-1 and at high-z up to z ~ 5, sometimes extending over distances of 60-130 kpc. Galactic-scale outflows may be a primary driver of galaxy evolution through the removal of cool gas from star-forming regions to a galaxy's → halo or beyond.
Of or relative to the center of a galaxy.
Fr.: distance galactocentrique
The distance from the center of a galaxy.
1) Generally, a large body of → gas,
→ dust, and → stars
held together by their mutual → gravitational attraction
and ranging in mass from about 106 to
1013 Msun. If a galaxy also contains
→ dark matter its mass will be much larger.
Galaxies are grouped into three main categories: → spiral galaxy,
→ elliptical galaxy, and
→ irregular galaxy
(→ Hubble classification).
From L.L. galaxias "Milky Way," from Gk. galaxis (adj.),
from gala (genitive galaktos) "milk."
Kahkešân, short for (râh-e) kahkešân literally "the (path of the) chaff-draggers" or "trail of chaff," from kah, kâh "chaff, straw, hay" (Mid.Pers. kâh "chaff, straw;" cf. Pali kattha- "a piece of wood;" Skt. kastha- "stick;" Gk. klados "twig;" O.Ir. caill "wood;" Ger. Holz "wood;" E. holt; PIE *kldo-) + kešân pr.p. of kešidan/kašidan "to carry, draw, protract, trail, drag" (Mid.Pers. kešidan "to draw, pull;" Av. karš- "to draw; to plow," karša- "furrow;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base kwels- "to plow"). The term (râh-e) kahkešân may be a popular corruption of Mid. Pers. (râh-i) Kâwôsân "the path of Kâwos" referring to the Persian mythological king Kay Kâwôs, who built an eagle-propelled throne to fly to China, as recounted in the Dênkard and the Shâhnâmé.
Fr.: bimodalité des galaxies
The division of galaxies into a "red sequence" and a "blue sequence" in the → color-magnitude diagrams of galaxies involving large statistical surveys. In both sequences, redder galaxies tend to be brighter. The blue sequence is truncated at the red magnitude ~ -22, while the red sequence extends to brighter magnitudes. The division between the two classes of galaxies is associated with a critical stellar mass ~ 3 × 1010 Msun. Galaxies below the critical mass are typically blue, star forming spirals and reside in the field. Galaxies above the critical mass are dominated by red spheroids of old stars and live in dense environments (Kauffmann et al, 2003, MNRAS 341, 33 & 54).
Fr.: bulbe d'une galaxie
xuše-ye kahkašâni (#)
Fr.: amas de galaxies
An aggregation of galaxies, made up of a few to a few thousand members, which may or may not be held together by its own gravity. Same as → cluster of galaxies.
Fr.: formation de galaxies
Fr.: harcèlement galactique
Frequent, high speed galaxy → encounters within → galaxy clusters. Harassment can disturb the morphologies of the galaxies involved, often inducing a new → burst of star formation. Asymmetrical galaxies, → warps, → bars, and → tidal tails can all be produced through galaxy harassment.
Fr.: galaxie M87
The dominant member of the → Virgo cluster of galaxies, which contains some 2,000 galaxies. Also known as NGC 4486, it has an → apparent visual magnitude 9.6. Discovered in 1781 by Charles Messier, this → elliptical galaxy is located 55 million → light-years away from Earth in the constellation → Virgo. M87 is the home of several thousand billion stars, a → supermassive black hole (SMBH) and a family of roughly 15,000 → globular clusters. For comparison, our → Milky Way galaxy contains only a few hundred billion stars and about 150 globular clusters. M87 is characterized by a prominent kiloparsec scale → relativistic jet emitted by the central SMBH. As gaseous material from the center of the galaxy → accretes onto the black hole, the energy released produces a stream of subatomic particles that are accelerated to velocities near the → speed of light.
galaxy main sequence
rešte-ye farist-e kahkešânhâ
Fr.: séquence principale des galaxies
A scaling relation between the → star formation rate (SFR) in galaxies and the total stellar mass (M*) of the galaxies. This relation, colloquially called the "galaxy main sequence," extends over several orders of magnitudes in M* and out to → high redshifts, with a modest scatter of ~ 0.3 dex which includes both intrinsic scatter and measurement uncertainties. The existence of such tight scatter at all observed epochs suggests that most galaxies assembled their stellar mass fairly steadily rather than predominantly in → starburst episodes, implying that → mergers have a sub-dominant contribution to the global star formation history (Wuyts et al., 2011 ApJ 742, 96).
Fr.: vent violent
An unusually strong wind.
Gale, from gaile "wind," origin uncertain, perhaps from O.N. gol "breeze," or O.Dan. gal "bad, furious."
Tondbâb "gale," from tond "swift, rapid, brisk; fierce, severe," Mid.Pers. tund "sharp, violent;" Sogdian tund "violent;" cf. Skt. tod- "to thrust, give a push," tudáti "he thrusts;" L. tundere "to thrust, to hit" (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere "to thrust or bore through," from per- + tundere, as explained); PIE base *(s)teud- "to thrust, to beat" + bâd, → wind.
mâhhâ-ye Gâlile-yi (#)
Fr.: lunes galiléennes
Same as → Galilean satellites.
Galilean, of or pertaining to Galileo Galilei (1564-1642), Italian physicist and astronomer; → moon
Fr.: relativité galiléenne
The principle according to which the fundamental laws of physics are the same in all
frames of reference moving with constant velocity with respect to one another
(→ inertial reference frames). Same as
→ Galilean invariance and
→ Newtonian relativity.
After Galileo Galilei (1564-1642), the Italian physicist and astronomer, who first described this principle in 1632; → relativity.
Fr.: satellites galiléens
tarâdis-e Gâlile-yi (#)
Fr.: transformation galiléenne
The method of relating a measurement in one → reference frame to another moving with a constant velocity with respect to the first within the → Newtonian mechanics. The Galilean transformation between the coordinate systems (x,y,z,t) and (x',y',z',t') is expressed by the relations: x' = x - vt, y' = y, z' = z. Galilean transformations break down at high velocities and for electromagnetic phenomena and is superseded by the → Lorentz transformations.
Galilean, of or pertaining to Galileo Galilei (1564-1642), Italian physicist and astronomer; → transformation.
Fr.: sonde Galileo
A space mission whose main goal was to explore → Jupiter and its moons and rings. The spacecraft was launched on October 19, 1989, arrived at Jupiter in December 1995. It disappeared on September 21, 2003, after eight years orbiting Jupiter, when mission controllers crashed it into → Jupiter's atmosphere. On December 7, 1995, Galileo's probe dived into Jupiter's atmosphere, and measured atmospheric pressure, density, and composition, and explored the planet's → radiation belts. Galileo had two parts: an orbiter and a descent probe that parachuted into Jupiter's atmosphere. The orbiter sent back hundreds of pictures of the four large → Galilean satellites of Jupiter (→ Io, → Europa, → Ganymede, and → Callisto). It made many discoveries during its eight years looping around Jupiter. It found evidence for layers of salt water below the surface on Europa, Ganymede, and Callisto, and measured high levels of volcanic activity on Io. When → Shoemaker-Levy slammed into Jupiter in 1994, Galileo had the only direct view of the → comet striking Jupiter's atmosphere. Galileo determined that → Jupiter's rings are formed from dust hurled up by → meteorite impacts on planet's inner moons. Measurements by the orbiter's → magnetometer revealed that Io, Europa, and Ganymede have metallic cores, while Callisto does not. Also, Galileo discovered that Ganymede possesses its own → magnetic field; it is the first moon known to do so. The orbiter also found that the Galilean satellites all have thin atmospheres. During it's trip from Earth to Jupiter, Galileo passed by and studied two asteroids: → Gaspra in 1991 and → Ida in 1993, around which it discovered → Dactyl, the first moon orbiting an asteroid (windows2universe.org).
Galileo's law of falling bodies
qânun-e Gâlilé darbâre-ye oft-e jesmhâ
Fr.: loi galiléenne de la chute des corps
In the absence of air resistance, any two bodies that are dropped from rest at the same moment will reach the ground at the same time regardless of their mass.