Alphekka (α Coronae Borealis)
Also known as Gemma, the brightest star in Corona Borealis (visual magnitude 2.23). Alphekka is an A type dwarf lying at about 7 → light-years. Actually it has a faint Sun-like (G5 V) companion, that produces an eclipse of the primary every 17.4 days.
Alphekka, from Ar. Nayyir al-Fakkah "the bright of the broken" (ring of star), from Nayyir "bright" + fakkah "broken," from fakk "to disjoin, unloose".
Meteorology: Small, faintly colored rings of light surrounding the → antisolar point, seen when looking down at a water cloud. Same as glory.
Pâdafsar, from pâd-, → anti- + afsar
black hole corona
tâj-e siyah câl
Fr.: couronne du trou noir
A spherical volume of hot plasma over a broader → accretion disk around a → black hole. The observation of energetic X-ray emission from black holes, which is inconsistent with → thermal emission from an accretion disk, is attributed to the presence of a putative hot corona. It has been widely postulated that the → hard X-rays are the product of → inverse Compton scattering of seed photons from accretion disks by hot ccoronae (See, e.g., F.L. Vieyro et al., 2010, arXiv:1005.5398 and R. C. Reis & J. M. Miller, 2013, arXiv:1304.4947).
tâj, hurtâj (#)
1) The outermost atmosphere of the Sun immediately above the
→ chromosphere, which can be seen during a total Solar eclipse.
It consists of hot (1-2 × 106 K), extremely tenuous gas (about 10-16
g cm-3) extending for millions of kilometer from the Sun's surface.
L. corona "crown, garland," cf. Gk. korone "anything curved, kind of crown."
Tâj "crown," loanword in Arm. tag "crown," tagavor "king," Proto-Iranian *tâgâ-, maybe from PIE base *(s)teg- "to cover" (L. toga "a garment worn by male citizens in ancient Rome;" hurtâj, from hur, → sun, + tâj.
tâj-e hudari, šomâli
Fr.: Couronne australe
The Southern Crown. A small, faint southern → constellation, also called Corona Austrini. Abbreviation: CrA, genitive: Coronae Australis.
→ corona; L. australis "southern."
tâj-e daštari, ~ jonubi
Fr.: Couronne boréale
The Northern Crown. A small but prominent northern → constellation that lies east of → Arcturus, between → Boötes and → Hercules, and comprises a distinctive arc formed by the stars seven stars. Abbreviation: CrB; genitive: Coronae Borealis.
→ corona; L. borealis "northern."
hurtâjnegâr (#), tâjnegâr (#)
An instrument which, when used in a telescope, produces an artificial eclipse, permitting the study of the → solar corona without a total eclipse of the Sun. It was invented in 1930 by the French astronomer Bernard Lyot (1897-1952).
tâji (#), hurtâji (#)
Of or relating to a → corona.
Fr.: condensation coronale
A part of the → solar corona where the gas density and the temperature are higher than in its vicinity. The coronal condensations are visible on the solar limb, above → sunspot groups. Images in X-rays and those supplied by → coronagraphs in white light reveal that such condensations consist of structures in the form of nodes, underlining the corona magnetic field (M.S.: SDE).
Fr.: motifs coronaux
Fr.: gaz coronal
A component of the → interstellar medium in the Galaxy which appears as pockets of gas at temperatures of over one million degrees, but extremely low densities of 104 atoms per cubic centimeter. The hot coronal gas is believed to be material blown out of violent supernova explosions. It is called "coronal gas", after a similarity with the hot gas in → solar corona.
Fr.: trou coronal
An area in the → solar corona which appears dark in X-rays and ultraviolet light. The gas density in these areas are very low, about 100 times less than that of coronal → active regions. The magnetic field lines in a coronal hole extend out into → interplanetary space rather than returning to the Sun's surface, as they do in other parts of the Sun (→ open magnetic field line). Ionized hot gas can escape easily along such a path, and this brings about high speed → solar wind streams.
Fr.: raie coronale
An → emission line in the spectrum of the → solar corona caused by highly ionized metal ions; especially those of iron, such as the red and green lines at 6375 Å and 5303 Å [Fe X] (Fe9+ ion) and [Fe XIV] (Fe13+ ion), respectively. From their discovery in 1870 until 1939, it was believed that these → forbidden lines would be due to an unknown element, called → coronium. Ultraviolet and X-ray coronal lines are also detectable in stars.
Fr.: boucle coronale
An arc-like structure in the Sun's → corona that is found around → sunspots and in → active regions. These structures are associated with the closed magnetic field lines that connect magnetic regions on the solar surface. The loops are sometimes as high as 10,000 km with their two ends situated in photosphere regions of opposite magnetic polarity. This implies that the coronal loops are tubes of magnetic flux filled with hot plasma. They last for days or weeks but most change quite rapidly.
coronal mass ejection (CME)
ešâneš-e jerm az hurtâj
Fr.: éjection de masse coronale
A huge eruption of material from regions of the solar corona in which the magnetic field is closed, but which suffer an extremely energetic disruption. Over the course of several hours up to 10,000 billion kg of this material is ejected into → interplanetary space with a a speed of as high as 3000 km/s. CMEs are most spectacularly observed by a white light coronagraph located outside Earth's atmosphere. Such observations from Skylab in the early 1970's were the first to reveal this phenomenon. CME's disrupt the flow of the → solar wind and can produce intense electromagnetic disturbances that can severely damage satellites and disrupt power grids on Earth. When these ejections reach the Earth, they give rise to → geomagnetic storms. The frequency varies with the → solar cycle; during solar minimum they come at a rate of about one per week, and during maximum there is an average of about two or three per day. See also → interplanetary coronal mass ejections (ICME).
Fr.: pluie coronale
Material that condenses in the Sun's corona and appears to rain down into the chromosphere, as observed at the solar limb above strong sunspots.
Fr.: grand jet coronal
A bright, narrow stream of particles traveling through the Sun's corona, visible in images taken with a coronagraph or during a total solar eclipse. Coronal streamers represent the most outwardly extended structures in the solar corona and result from the interaction between the solar slow wind and the large-scale magnetic field. → helmet streamer.
Fr.: couronne E
A part of the → solar corona defined by the → emission lines of hot gases. These emission lines include the so-called → forbidden lines of the strongly ionized atoms of iron, calcium, and other elements. The E corona is thinner than the → K corona and the → F corona (M.S.: SDE).
Fr.: couronne F
The exterior part of the → solar corona, illuminated by solar light scattered or reflected by dust particles. The same phenomenon also produces the → zodiacal light, much farther away from the Sun. The dust particles are at most several microns in size and make up a disk stretching over almost 1 solar radius (700,000 km) from the Sun's surface. Unlike electrons, which are responsible for the → K corona, the dust particles move relatively slowly. Thus, the light scattered by them has the same spectrum as the → photosphere and shows the → Fraunhofer lines. The F corona is the most luminous part of the corona at 1.5 solar radii from the Sun's surface (M.S.: SDE).
F referring to the Fraunhofer lines; → corona.
The outermost part of Earth's atmosphere, a tenuous halo of hydrogen and some helium extending out to perhaps 15 Earth radii, which emits Lyman-alpha radiation when it is bombarded by sunlight.