Fr.: Quintet de Stéphan
A group of five closely grouped galaxies (NGC 7317, 7318A, 7318B, 7319 and 7320) in the constellation → Pegasus. Four of the galaxies show essentially the same → redshift, suggesting that they are at the same distance from us. The fifth galaxy (NGC 7320) has a smaller redshift than the others, indicating it is much closer. This one is probably a foreground galaxy which happens to lie along the line of sight. The four distant galaxies seem to be colliding, showing serious distortions due to gravitational → tidal forces. The NASA → Spitzer Space Telescope has revealed the presence of a huge intergalactic → shock wave. Collisions play an important role in the life cycles of galaxies. → merging galaxies.
Of, relating to, or being a delineation of the form of a solid body on a plane.
Fr.: projection stéréographique
A graphical method of depicting three-dimensional geometrical objects in two dimensions. In a → planispheric astrolabe, it is the projection of a point of the celestial sphere onto the equatorial plane, as seen from one of the poles. The center of projection is the South pole for the northern hemisphere, and the North pole for the southern hemisphere. In this operation the projection of any circle of the sphere remains a circle on the projection plane and moreover the projection does not alter angles.
The process or art of depicting solid objects on a plane surface.
Of, relating to, or determined by → stratigraphy.
cine-šenâsi (#), cine-negâri
The study of → sedimentary rock units, including their geographic extent, age, classification, characteristics and formation.
The second major layer of Earth's atmosphere, just above the → troposphere and below the → mesosphere, extending from about 20 km to 90 km above the Earth. It is characterized by little vertical increase in temperature.
From Fr. stratosphère, literally "sphere of layers," coined by Fr. meteorologist Léon-Philippe Teisserenc de Bort (1855-1913) from L. stratus "a spreading out" (from p.p. stem of sternere "to spread out") + -sphère (→ sphere), as in atmosphère.
Of, relating to, or characteristic of the stratosphere.
Stratospheric Observatory for Infrared Astronomy (SOFIA)
Nepâhešgâh-e Cine-sepehri barây axtaršenâsi-ye forusorx
Fr.: Observatoire stratosphérique pour l'astronomie infrarouge
A partnership of NASA and the German Aerospace Center, consisting of an extensively modified Boeing 747SP aircraft carrying a reflecting telescope with an effective diameter of 2.5 m. NASA Ames Research Center manages SOFIA's science and mission operations in cooperation with the Universities Space Research Association and the German SOFIA Institute. SOFIA is the largest airborne observatory in the world, with a planned 20-year lifetime.
sepehr-e Stömgren, kore-ye ~
Fr.: sphère de Strömgren
A theoretical sphere of → ionized hydrogen created by energetic → ultraviolet→ photons of a hot, → massive star embedded in a uniform interstellar → molecular cloud and lying at the center of the sphere. → H II region.
Named after Bengt Strömgren (1908-1987), a Danish astrophysicist, who put forward the first and simplest version of the model in 1939; → sphere.
A general term for materials of all types and sizes that are ejected by volcanic eruptions. It includes particles as tiny as volcanic ash and as large as bombs and blocks.
From Gk. tephra "ashes."
axtarfizik-e negarik (#)
Fr.: astrophysique théorique
An astrophysical study or research group mainly concerned with theory rather than observation.
The region of the upper atmosphere in which temperature increases continuously with height, starting at roughly 100 km. The thermosphere includes the exosphere and most of the ionosphere.
Any of several techniques, such as → Doppler tomography, for constructing a spatial distribution of physical quantity given measurements that are essentially line-integrals ("projections") through the distribution. Most famously, in medical tomography, the absorption of X-rays by a specimen is directly related to the line integral to make detailed images of a predetermined plane section of a solid object while blurring out the images of other planes.
From Gk. tomo- combining form of tomos "a cut, section, slice" tome "cutting" + → -graphy.
Borešnegâri, from boreš "section, slice, cutting," from boridan "to cut" (Mid.Pers. britan, brinitan "to cut off;" Av. brī- "to shave, shear," brin-; cf. Skt. bhrī- "to hurt, injure," bhrinanti "they hurt") + -negâri, → -graphy.
transient lunar phenomenon (TLP)
padide-ye mângi-ye gozarâ, ~ mâhi-ye
Fr.: phénomène lunaire transitoire
A short-lived change in the brightness of patches on the face of the Moon. The TLPs last from a few seconds to a few hours and can grow from less than a few to a hundred kilometers in size. They have been reported by many observers since the invention of the telescope. However, the physical mechanism responsible for creating a TLP is not well understood. Several theories have been proposed, among which lunar outgassing, that is, gas being released from the surface of the Moon.
A compound → vowel sound resulting from the succession of three simple vowels pronounced in a single syllable (as in power, hour, fire).
triple alpha process
farâravand-e âlfâ-ye setâyi
Fr.: réaction triple alpha
A chain of nuclear fusion reactions by which three helium nuclei (→ alpha particles) are transformed into → carbon. First two nuclei of helium collide, fuse, and form a nucleus of → beryllium: 4He + 4He ↔ 8Be, which is unstable and will decay back into two helium nuclei within a few 10-17 seconds. However, due to sufficiently high density and temperature in the stellar core, during a third collision between beryllium and helium, carbon is formed: 8Be + 4He → 12C + γ. The triple-alpha process is possible owing to the existence of the → Hoyle state. It is the main source of energy production in → red giants and → red supergiants in which the core temperature has reached at least 100 million K. Also called → Salpeter process.
The lower part of the Earth's atmosphere in which temperature decreases with height, except for local areas of → temperature inversion.
Fr.: émission à deux photons
The simultaneous emission of two photons whose sum of energies is equal to that of a single electron transition. The energy of each individual photon of the pair is not fixed, so that the spectrum of two-photon emission is continuous from the wavelength of that transition to infinity. In practice, there is a peak in wavelength distribution of the emitted photons. Two-photon emission is studied atomic physics with application in astrophysics, as it contributes to the continuum radiation from → planetary nebulae. It was recently observed in condensed matter and specifically in → semiconductors.
Fr.: céphéide à très courte période