radebandi-ye Hubble (#)
Fr.: classification de Hubble
The classification of galaxies according to their visual appearance into four basic types suggested by E. Hubble: → ellipticals (E), → spirals (S), → barred spirals (SB), and → irregulars (Ir). Later on a separate class of → lenticulars (S0) was appended as an intermediate type between ellipticals and spirals. The sequence starts with round elliptical galaxies (E0). Flatter galaxies are arranged following a number which is calculated from the ratio (a - b)/a, where a and b are the major and minor axes as measured on the sky. Ellipticals are divided into eight categories (E0, E1, ..., E7). Beyond E7 a clear disk is apparent in the lenticular (S0) galaxies. The sequence then splits into two parallel branches of disk galaxies showing spiral structure: ordinary spirals, S, and barred spirals, SB. The spiral and barred types are subdivided into Sa, Sb, Sc, and SBa, SBb, SBc, respectively. Along the sequence from Sa to Sc, the central bulge becomes smaller, while the spiral arms become more and more paramount. The original, erroneous idea that such arrangement of the galaxies might represent an evolutionary sequence led to the ellipticals being referred to as early-type galaxies, and the spirals and Irr I irregulars as late-type galaxies. See also → dwarf galaxy, → dwarf elliptical galaxy, → dwarf spheroidal galaxy.
pâyâ-ye Hubble (#)
Fr.: constante de Hubble
The → Hubble parameter for the present epoch. It is the constant of proportionality between the → recession velocities of galaxies and their distances from each other. The latest determinations using the → Hubble Space Telescope observations of → Cepheids give H0 = 72 ± 8 km s-1 Mpc-1 (W. L. Freedman et al., 2001, ApJ 553, 47, arXiv:astro-ph/0012376), the → WMAP observations yield 70.4 ± 1.3 km s-1 Mpc-1 (N. Jarosik et al., 2011, ApJS 192, 14, arXiv:1001.4744), and the → Planck Satellite observations give 67.3 ± 1.2 km s-1 Mpc-1 (Planck Collaboration, 2014, A&A 571, A16, arXiv:1303.5076). More recently, the Hubble constant was derived by a team of astronomers, using the NASA/ESA Hubble Space Telescope, with a 2.4% accuracy (Adam G. Reiss et al., 2016, arXiv:1604.01424). The new value, 73.2 km s-1 Mpc-1, suggests that the Universe is expanding between five and nine percent faster than previously calculated. The → Hubble law is only applicable for large distances (> 20 Mpc), when the proper motions of galaxies in groups and clusters cannot confuse the recession due to expansion.
Hubble Deep Field (HDF)
meydân-e žarf-e Hubble (#)
Fr.: champ profond de Hubble
An image of a small region in the constellation → Ursa Major, based on the results of a series of observations by the → Hubble Space Telescope. The image was assembled from 342 separate exposures taken over ten consecutive days between December 18 and December 28, 1995. It covers an area 144 arcseconds across.
nemudâr-e Hubble (#)
Fr.: diagramme de Hubble
Fr.: distance de Hubble
Fr.: flot de Hubble
The general outward motion of galaxies resulting from the → expansion of the Universe.
Fr.: loi de Hubble
→ Hubble's law.
Fr.: longueur de Hubble
Fr.: paramètre de Hubble
The rate pf change of the → cosmic scale factor: H(t) = (dR/dt)/R. The Hubble parameter is a time-dependent quantity and therefore is not constant. The → Hubble constant is the Hubble parameter measured today.
šo'â'-e Hubble (#)
Fr.: rayon de Hubble
Fr.: séquence de Hubble
A classification scheme in which galaxies are ordered into a sequence based on their morphology. Same as the → Hubble classification.
Hubble Space Telescope (HST)
durbin-e fazâyi-ye Hubble, teleskop-e ~ ~ (#)
Fr.: télescope spatial de Hubble
A telescope of 2.4 m in diameter, a joint NASA and ESA project, launched in 1990 into a low-Earth orbit 600 km above the ground. It was equipped with a collection of several science instruments that worked across the entire optical spectrum (from infrared, through the visible, to ultraviolet light). During its lifetime Hubble has become one of the most important science projects ever.
zamân-e Hubble (#)
Fr.: temps de Hubble
An estimate for the age of the Universe by presuming that the Universe has always expanded at the same rate as it is expanding today. It is the inverse of the → Hubble constant: tH = 1/H0. Also called the Hubble age or the Hubble period.
qânun-e Hubble (#)
Fr.: loi de Hubble
The speed with which a galaxy recedes from us is directly proportional to its distance. Hubble's "law" is only statistically correct, as individual galaxies can have quite large random velocities around this overall → Hubble flow. It should be underlined that Hubble was not the first to discover the → velocity-distance relation. Two years before Hubble, in 1927, Georges Lemaître (1894-1966) had derived the relation and published it in a paper in French which remained neglected (→ Friedmann-Lemaitre Universe).
After Edwin Hubble (1889-1953), the American astronomer who published his results in 1929; → law.
Fr.: classification de Hubble-Sandage
Same as the → Hubble classification.
Fr.: variable de Hubble-Sandage
A type of highly luminous → blue supergiant star with variable light, first discovered in the M31 and M33 galaxies; also called → S Doradus stars. They are now believed to be part of the class of → Luminous Blue Variable stars.
→ Hubble; Allan Rex Sandage (1926-2010), American cosmologist.
Fr.: Trou Géant
A region of the Universe, nearly a billion light-years across, mostly devoid of stars, gas, other normal matter, and also → dark matter. Situated at about 6 billion light-years from us, in projection on the the constellation → Eridanus, it shows up as a particularly cold region in the map of the → cosmic microwave background (CMB) radiation. Observations made using the → Very Large Array (VLA) radio telescope show a relative absence of matter in that area.
Surâx, → hole; kalân "great, large, bulky."
Fr.: courbe de Hugoniot
A curve, on the pressure versus specific volume plane, representing the locus of all the possible states that can be reached by a substance immediately after the passage of a single → shock wave. For each initial condition there is a different curve. No combustion occurs in the process and, therefore, the chemical composition of the medium does not change. See also → Rayleigh line; → Crussard curve.
Named after the French physicist Pierre Henri Hugoniot (1851-1887), who worked on fluid mechanics, especially flow properties before and after shock waves; → curve.
Hulse-Taylor pulsar (PSR 1913+16)
tapâr-e Hulse-Taylor, pulsâr-e ~
Fr.: pulsar de Hulse-Taylor
A → pulsar with a period of 59 milliseconds (17 pulses per second) moving around a compact companion in an elongated orbit (period 7.75 hours). It is thought that the companion is probably also a → neutron star with the same mass as the pulsar (1.4 solar masses). The orbit is gradually shrinking because of → gravitational radiation, as predicted by the theory of → general relativity. See also → binary pulsar, → millisecond pulsar.
Named after the American physicists Russell Hulse and Joseph Taylor of Princeton University, who discovered the pulsar in 1974, for which they shared the 1993 Nobel prize in physics; → pulsar.
1) martugân; 2) martu
M.E. from M.F. humain, from L. humanus "of man, human," also "humane, kind, gentle, polite," probably related to homo "man," and to humus "earth," on notion of "earthly beings."
Martu, → man, + -gân a suffix forming nouns or adjectives denoting relation and plurality.