Hickson Compact Group (HCG)
goruh-e hampak-e Hickson
Fr.: groupe compact de Hickson
A list of 100 compact groups of galaxies that were identified by a systematic search of the → Palomar Observatory Sky Survey red prints. Each group contains four or more galaxies, has an estimated mean surface brightness brighter than 26.0 magnitude per arcsec2 and satisfies an isolation criterion.
Himalia (Jupiter VI)
The tenth of Jupiter's known satellites, 186 km in diameter revolving at a mean distance of 11,480,000 km from Jupiter. Discovered in 1904 by the Argentine-American astronomer Charles Dillon Perrine (1867-1951).
Himalia was a nymph of the island of Rhodes. She was seduced by the god Zeus (Jupiter).
abar-now-axtar-e târixi (#)
Fr.: supernova historique
A supernova event recorded in the course of history before the invention of the telescope. The well recorded supernovae of this small group are SN 185, SN 1006, SN 1054 (→ Crab Nebula), SN 1181, SN 1572 (→ Tycho's star), and SN 1604 (→ Kepler's star).
Fr.: Jupiter chaud
A giant, gaseous, Jupiter-like planet lying too close to its parent star and having an orbital period from a few days to a few weeks. The existence of hot Jupiters is usually interpreted in terms of planetary migration. These planets can, in principle, be formed at larger distances from their stars and migrate to the inner regions due to dynamical interaction with the proto-planetary disk.
hydroxyl group (OH)
goruh-e hidroksil (#)
Fr.: groupe hydroxyle
The univalent radical or group consisting of one hydrogen and one oxygen atom, forming a part of a molecule of a compound.
From → hydro- + ox(y)- a combining form meaning "sharp, acute, pointed, acid," used in the formation of compound words, from Gk, oxys "sharp, keen, acid" + -yl a suffix used in the names of chemical radicals, from Fr. -yle, from Gk. hyle "matter, substance;" → group.
A group to which the speaker, the person spoken of, etc. belongs.
Xodi "insider, familiar, friend," from xod "own," → self-.
Io (Jupiter I)
1) The fifth of → Jupiter's known moons and
the third largest. It is the innermost of the
→ Galilean satellites.
With a diameter of 3630 km, Io is slightly larger than Earth's Moon. It revolves at
a mean distance of 422,000 km from Jupiter.
Its mass is 8.93 x 1022 kg (about 1.2 Earth Moons) and its
→ orbital period 1.8 Earth days.
The mean → surface temperature
of Io is -155 °C.
Io's yellow color derive from → sulfur
and molten → silicate rock. The unusual
surface of Io is kept very young by its system of active
The intense → tidal force
of Jupiter stretches Io and
damps wobbles caused by Jupiter's other Galilean moons. The resulting
friction greatly heats Io's interior, causing molten rock to explode
through the surface. Io's volcanoes are so active that they are
effectively turning the whole moon inside out. Some of Io's volcanic
lava is so hot it glows in the dark.
In Gk. mythology, Io was a maiden who was seduced by Zeus (Jupiter). When Hera came upon their rendez-vous, Zeus transformed the maiden into a white heifer.
jofteš-e jj, jafsari-ye ~
Fr.: couplage jj
A coupling scheme of electronic → spin angular momenta and → orbital angular momenta for heavy atoms (generally Z > 30), where the spin and orbital angular momenta of individual electrons couple strongly, and therefore the → LS coupling scheme does not apply. The coupling between spin and orbital angular momentum of each electron is much stronger than the coupling between different electrons. Therefore, the total angular momentum, ji, for the i-th electron is obtained by combining li and si and then coupling these j's together to give the total angular momentum J = Σi ji. In the jj coupling scheme the total orbital angular momentum quantum number, L, and the total spin angular momentum number, S, are not specified.
j referring to the symbol of the total angular momentum for individual electrons; → coupling.
The largest → planet in the → Solar System and the fifth from the Sun, lying at a mean distance of about 5.2 → astronomical units from the Sun. Jupiter is a → gas giant, mostly → hydrogen and → helium, with a mass of 1.898 × 1027 kg, or about 0.001 → solar masses, or 318 times → Earth masses. It is more than twice as massive as all the other solar system planets combined. Jupiter's diameter measures 11 times that of Earth. Its → rotation period, 9.93 hours (Jupiter/Earth ratio = 0.41), is the shortest of all the solar system planets. Its → orbital period is 11.857 Earth years. Jupiter has an extensive family of → satellites (79 known) and a faint → ring system; → Jupiter's ring. Jupiter probably has a core of rocky material amounting to something like 10 to 15 Earth masses. Above the core lies the main bulk of the planet in the form of liquid → metallic hydrogen. This exotic form of the most common of elements is possible only at pressures about 3 million bars, as is the case in the interior of Jupiter (and Saturn). Under the extreme pressure found deep inside Jupiter, the electrons are released from the hydrogen molecules and are free to move about the interior. This causes hydrogen to behave as a metal; it becomes conducting for both heat and electricity. See also → Jupiter's atmosphere.
Jupiter "the king of ancient Roman gods, the ruler of Olympus," from L. Iupeter, from PIE *dyeu-peter- "god-father," from *deiw-os "god" (cf. Pers. div "devil, demon;" Mid.Pers. dêw; O.Pers. daiva- "evil god, demon;" Av. daēva- "evil spirit, false god;" Skt. deva-; Gk. Zeus "supreme god;" from *dei- "to gleam, to shine") + *peter "father" (cf. Pers. pedar "father;" O.Pers. pitā- "father;" Av. patar-, ptā-; Skt. pitár-; Gk. pater; L. pater, O.H.G. fater).
Hormoz, from Mid.Pers. Ohrmazd "name of the highest god in Zoroastrianism," from O.Pers. aura-mazdā-, Av. ahura-mazdā- "Wise Lord," from ahura- "lord, god;" cf. Skt. ásura- "god, lord;" Hittite hassu- "king;" M.H.G. Asen "name of a group of gods;" O.N. āss "god;" PIE *ansu- "spirit, demon" + mazdā- "wisdom," mazdāθa- "what must be borne in mind," mazdāh- "memory;" cf. Skt. medhā- "mental power, wisdom, intelligence;" Gk. mathein "to learn, to know" (root of → mathematics).
JUpiter ICy moons Explorer (JUICE)
Puyešgar-e Mânghâ-ye Yaxi-ye Hormoz
Fr.: Jupiter ICy moons Explorer
An interplanetary mission currently in development by the → European Space Agency planned for launch in 2020. It is aimed mainly at in-depth studies of three potentially ocean-bearing satellites, → Ganymede, → Europa, and → Callisto. JUICE will complete a unique tour of the Jupiter system including several flybys of each planet-sized world, culminating with orbit insertion around Ganymede, the largest moon in the Solar System, followed by nine months of operations in its orbit. JUICE will carry the most powerful scientific payload ever flown to the outer Solar System. It consists of 10 state-of-the-art instruments plus one experiment that uses the spacecraft telecommunication system with ground-based instruments.
Fr.: masse de Jupiter
A quantity of mass equal to 1.898 × 1027 kg, about 0.000954 → solar masses, or 317.83 → Earth masses. Jupiter mass, MJ, is used as a → unit to describe masses of the → gas giant, such as the outer planets and → extrasolar planets. Similarly, → brown dwarf masses are expressed in terms of Jupiter mass.
javv-e Hormoz, havâsepehr-e ~
Fr.: atmosphère de Jupiter
The gaseous envelope surrounding Jupiter. It is about 90% → hydrogen and 10% → helium (by numbers of atoms, 75/25% by mass) with traces of → methane, → water, and → ammonia. This is very close to the composition of the primordial → solar nebula from which the entire solar system was formed. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium. The outermost layer is composed primarily of ordinary → molecular hydrogen and helium. Visually, Jupiter is dominated by two atmospheric features; a series of ever-changing atmospheric cloud bands arranged parallel to the equator and an oval atmospheric blob called the → Great Red Spot.
Fr.: anneaux de Jupiter
Any of several faint, dark, narrow rings around Jupiter. Jupiter's rings are so faint and tenuous that are only visible when viewed from behind Jupiter and are lit by the Sun, or directly viewed in the infrared where they faintly glow. Unlike → Saturn's rings full of large icy and rock chunks, they are composed of tiny rock fragments and dust. Jupiter's rings are continuously losing material and being resupplied with new dust from → meteorite impacts with Jupiter's four inner moons (→ Metis, → Adrastea, → Amalthea, and → Thebe). Jupiter's rings were discovered by NASA's Voyager 1 in 1979. They are composed of three parts: the → Main ring, a → Halo ring that orbits closer to Jupiter, and a very wide → Gossamer ring that extends far from Jupiter.
kinematically decoupled core (KDC)
maqze-ye jonbešikâné vâjafsaridé
Fr.: cœur cinématiquement découplé
A central, tightly bound stellar subsystem observed in some elliptical galaxies which rotates in the opposite direction with respect to the main body of the → elliptical galaxy. Elliptical galaxies are thought to be the result of the → merger of two or more sizable galaxies. A plausible scenario for how counter-rotating cores could form in such a merger is as follows. If at least one of the galaxies has a core region that is fairly tightly bound by the galaxy's gravity, and the direction in which the two galaxies orbit each other before merging is opposite to the direction of rotation of stars in that tightly bound core, it is likely that, after the merger, the tightly bound core will end up as the core of the new, larger galaxy, while retaining its original sense of rotation. The surrounding stars, on the other hand, will rotate in a different way dictated by the orbital motion of the galaxies around each other, before the merger. While this is a plausible scenario, it can only explain some of the counter-rotating cores. Recently A. Tsatsi et al. (2015, ApJ 802, L3) have shown that although the two → progenitor galaxies are initially following a → prograde orbit, strong reactive forces during the merger can cause a short-lived change of their orbital spin; the two progenitors follow a → retrograde orbit right before their final coalescence. This results in a central kinematic decoupling and the formation of a large-scale (~2 kpc radius) counter-rotating core at the center of the final elliptical-like merger remnant, while its outer parts keep the rotation direction of the initial orbital spin.
Fr.: L2 Puppis
A → semiregular variable with a period of 141 days. It has a → spectral type of M5 III corresponding to an → effective temperature of ~ 3500 K. It has a radial velocity relative to the → Local Standard of Rest of 33.3 km s-1. At a distance of 64 → parsecs, L2 Pup is the second nearest → asymptotic giant branch (AGB) star next to R Doradus; it is ~ 30% closer than → Mira. Recent → near-infrared JHKL band observations by Kervella et al. (2014, 2015) show a compact dust disk around the central star, with an inner rim of 6 → astronomical units and an outer edge of 13 au, at an inclination of approximately 82°. The → circumstellar environment of L2 Pup was observed with → ALMA. The → molecular emission shows a → differentially rotating disk, inclined to a nearly edge-on position (Homan et al., 2017, A&A 601, A5 and references therein).
Fr.: superamas Laniakea
A → supercluster of galaxies that includes our → Local Group and about 300 to 500 known → galaxy clusters and groups. Also called → Local Supercluster. If approximated as round, it has a diameter of 12,000 km s-1 in units of the → cosmic expansion or 160 megaparsecs, and encompasses about 1017 → solar masses. Our Local Group lies toward the outer regions of Laniakea. Its main components are the four previously known superclusters: → Virgo supercluster (the part where the → Milky Way resides), Hydra-Centaurus Supercluster (including the → Great Attractor, Antlia Wall, known as Hydra Supercluster, → Centaurus supercluster), Pavo-Indus Supercluster, and Southern Supercluster (including Fornax Cluster, Dorado and Eridanus clouds). The most massive galaxy clusters of Laniakea are Virgo, Hydra, Centaurus, Abell 3565, Abell 3574, Abell 3521, Fornax, Eridanus, and Norma. The Laniakea supercluster was discovered by Tully et al. (2014, Nature 513, 71).
From the Hawaiian words lani "heaven," and akea "spacious, immeasurable;" → supercluster.
Lesath (Upsilon Scorpii)
A bright blue star of → apparent visual magnitudeV = 2.70, that with → Shaula (Lambda Scorpii) makes up the Scorpion's stinger. Among its other designations: HR 6508 and HIP 85696. Lesath is 580 → light-years away. Lesath and Shaula appear very close on the sky (less than a degree apart), but they are not physically related. Lesath is a → subgiant of → spectral type B2 IV with a → luminosity of about 7,380 Msun. It has a radius of about 6 Rsun, and a → surface temperature of about 22,000 K.
Lesath, from Ar. al-Las'ah (
linear electric quadrupole
cahârqotbe-ye barqi-ye xatti
Fr.: quadrupôle électrique linéaire
A system of three charges +q, -2q, and +q, arranged along a line to form an axial quadrupole. The → electric potential V due to a linear quadrupole varies as 1/r3, whereas the → electric intensity E varies as 1/r4.
goruh-e mahali (#)
Fr.: Groupe local
A small → galaxy cluster of about 50 galaxies to which our → Milky Way galaxy belongs. The Local Group occupies a volume of space nearly 10 million → light-years across centered somewhere between the → Andromeda Galaxy (M31) and the Milky Way, which are the dominant galaxies of the group; Andromeda being the principal member. Both of these galaxies exhibit spiral structures, and each is attended by a large family of satellite → dwarf galaxies. The Local Group also includes a third spiral galaxy known as → Triangulum (M33), which is bound to Andromeda. The remaining members span a range of → Hubble classification types from dwarf spheroidal to Irr to Sb and Sc and cover a factor of 10 in → metallicity. The total mass of the Local Group is estimated to be about 2 × 1012 solar masses, although this value is still uncertain to within a factor of about 2. The velocities of the individual galaxies of the Local Group are not particularly high. Therefore no member is believed to be able to escape the group, which is thus considered to be gravitationally → bound. Another remarkable member of the Group is → IC 10.
abarxuše-ye mahali (#)
Fr.: superamas local
The supercluster to which the Local Group belongs. It is composed of some 100 clusters of galaxies, with the Virgo cluster of galaxies at its center.