An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Statistics: The square root of the arithmetic mean of the squares of the deviation of observed values from their arithmetic mean.

→ root; → mean; → square; → deviation.

In → graph theory, a → graph that has one of its → vertices, called the → root, distinguished from the others.

→ root; → graph.

In → graph theory, a → tree in which one → vertex is distinguished from the other vertices and is called the root.

→ root; → tree.

A German X-ray satellite developed through a cooperative program with the United States and the United Kingdom. The satellite, launched by a Delta rocket (Cape Canaveral) on June 1, 1990, operated until February 12, 1999. ROSAT consisted of two telescopes performing in the → soft X-ray (0.1-2.4 keV) and → extreme ultraviolet (EUV) (006-0.2 keV) ranges. It carried out the first → all-sky surveys with imaging X-ray and EUV telescopes leading to the discovery of 125,000 X-ray and 479 EUV sources. In addition the diffuse Galactic X-ray emission was mapped with unprecedented angular resolution (≤ 1 arcmin). Most of the mission time was devoted to pointed observations at selected targets. ROSAT imaged everything from nearby asteroids and comets to distant quasars during its 8-year mission. The main ROSAT data centers were and are at the Max Planck Institute for Extraterrestrial Physics in Garching (X-rays) and at the University of Leicester (EUV) with mirror sites at the Goddard Space Flight Center and other research institutes.

ROSAT, short for the → ROentgen→ SATellite, in honor of the German physicist.

A spacecraft launched in March 2004 by the → European Space Agency to be the first man-made object to orbit a → comet's → nucleus. Rosetta will also be the first spacecraft to fly alongside a comet as it heads toward → perihelion in the inner → solar system. After a ten-year voyage across the solar system, it will reach a → periodic comet known as Comet 67P/ → Churyumov-Gerasimenko. Rosetta will remain in close proximity to the icy nucleus as it plunges toward the warmer inner reaches of the Sun's realm. Rosetta orbiter's scientific payload includes 11 different instruments, in addition to a robotic lander and 10 solar panels spanning 32 m tip to tip. In November 2014, Rosetta will launch the 100 kg lander, named Philae, onto the comet. Philae will touch down and then fire a harpoon to anchor itself and prevent it from escaping the comet's weak gravity. The lander carries 10 instruments, including a drill to take samples of subsurface material. More than a year will pass before the remarkable mission comes to an end in December 2015. By then, both the spacecraft and the comet will have circled the Sun and will be on their way out of the inner solar system. Rosetta's prime objective is to help understand the origin and evolution of the solar system. The comet's composition reflects the composition of the pre-solar nebula out of which the Sun and the planets of the solar system formed, more than 4.6 billion years ago. Therefore, an in-depth analysis of comet 67P/Churyumov-Gerasimenko by Rosetta and its lander will provide essential information to understand how the solar system formed. Before arriving at 67P/Churyumov-Gerasimenk, Rosetta flew by the → asteroids 2867 → Steins and 21 → Lutetia in 2008 and 2010, respectively, and gathered data on them.

Named for the Rosetta Stone, a black stele that was inscribed with a royal decree (196 BC) in two languages using three scripts: Egyptian hieroglyphics, Egyptian Demotic, and Greek. The Rosetta Stone was found in a small village in the Nile Delta called Rashid (Rosetta) in 1799. The spacecraft's robotic lander is called Philae, after a similarly inscribed obelisk found on an island in the Nile River. Both the stone and the obelisk were key to deciphering ancient Egyptian hieroglyphs, carried out by Jean-François Champollion (1790-1832) in 1822. Astronomers hope the Rosetta mission will provide a key to many questions about the origins of the solar system.

A giant H II region of about 1° in diameter, lying about 5000 light-years away in the Milky Way, the constellation → Monoceros. It is ionized by the cluster NGC 2244, a group of hot young stars at the center of the nebula. Also called M16, the brighter portions of the nebula have been assigned different NGC numbers: 2237, 2238, 2239, and 2246.

Rosette "a rose-shaped ornament," from Fr. rosette, from O.Fr. rosette, diminutive of rose "rose;" L. rosa, probably from Gk. wrodon (Aeolic), then rhodon, a loan from Iranian, as below; → nebula.

Miq, → nebula; golsân "resembling rose, flower," from gol "flower, rose," variants vard (sohre-vard "red rose"), Semnâni dialect vela "rose;" Mid.Pers. *vard, gul, loaned in Arm. vard and Ar. ward; Av. varəδa- "rose;" loaned in Gk. wrodon (Aeolic), then rhodon; + -sân "manner, semblance" (variant sun, Mid.Pers. sân "manner, kind," Sogdian šôné "career").

A → red dwarf star of → spectral type M4. Other designations: Proxima Virginis, FY Virginis, GJ 447, HIP 57548, and LHS 315. With a distance of just 3.4 → parsecs, it is one of the brightest representatives of this subclass (V = 11.15, J = 6.51, H =5.95, K = 5.65 mag). It is the 13th closest (sub-)stellar system to the Sun, including → brown dwarfs. Ross 128 is moving toward us and will actually become our closest neighbor in just 71,000 years from now. Ross 128 has an → effective temperature, T_eff = 3192, a mass of 0.168 Msun (→ solar mass), a → luminosity of 0.00362 Lsun (→ solar luminosity), a radius of 0.017 Rsun (→ solar radius), and a → metallicity [Fe/H] of -0.02. An Earth-sized → exoplanet, → R 128 b, orbits Ross 128 (Bonfils et al., 2017, arXiv:1711.06177).

Star number 128 in the → Ross Catalogue.

An → extrasolar planet around the → red dwarf star → R 128. The → exoplanet orbits its star every 9.9 days. This Earth-sized world is expected to be temperate, with a surface temperature that may also be close to that of the Earth. Many red dwarf stars, including → Proxima Centauri, are subject to → flares that occasionally bathe their orbiting planets in deadly → ultraviolet and → X-ray radiation. However, it seems that Ross 128 is a much quieter star, and so its planets may be the closest known comfortable abode for possible life. Ross 128 b orbits 20 times closer than the Earth orbits the Sun. Despite this proximity, it receives only 1.38 times more irradiation than the Earth. As a result, Ross 128 b's equilibrium temperature is estimated to lie between -60 and 20°C, thanks to the cool and faint nature of its small red dwarf host star, which has just over half the surface temperature of the Sun.

The letter b, designates the first exoplanet discovered around → R 128.

Ross, Frank E., 1926, "New proper-motion stars, (second list)", Astronomical Journal 36, 856.

Frank Elmore Ross (1874-1960) was the succeeded to E. E. Barnard at Yerkes Observatory. He inheriting Barnard's collection of photographic plates. Ross decided to repeat the same series of images and compare the results with a → blink comparator. He discovered 379 new variable stars and over 1000 stars of high proper motion.

A dimensionless number relating the ratio of inertial to Coriolis forces for a given flow of a rotating fluid. It is used in the study of atmospheric motions in planets. In case a small number is involved, cyclones and anticyclones are observed for low and high pressures. When it is large (Venus) the Coriolis force becomes negligible and atmospheric motions are barely affected by planetary rotation.

Named after Carl-Gustav Arvid Rossby (1898-1957), a Swedish-American meteorologist who first explained the large-scale motions of the atmosphere in terms of fluid mechanics; → number.

The northward variation of the Coriolis parameter, arising from the sphericity of the Earth.

→ Rossby number; → parameter.

A wave on a uniform current in a two-dimensional non-divergent fluid system, rotating with varying angular speed about the local vertical.

→ Rossby number; → wave.

The → opacity of a gas of given composition, temperature, and density averaged over the various wavelengths of the radiation being absorbed and scattered. The radiation is assumed to be in → thermal equilibrium with the gas, and hence have a → blackbody spectrum. Since → monochromatic opacity in stellar plasma has a complex frequency dependence, the Rosseland mean opacity facilitates the analysis. Denoted κ_R, it is defined by: 1/κ_R = (π/4σT³) ∫(1/k_ν) (∂B/∂T)_νdν, summed from 0 to ∞, where σ is the → Stefan-Boltzmann constant, T temperature, B(T,ν) the → Planck function, and k_ν monochromatic opacity (See Rogers, F.J., Iglesias, C. A. Radiative atomic Rosseland mean opacity tables, 1992, ApJS 79, 507).

Named after Svein Rosseland (1894-1985), a Norwegian astrophysicist, who obtained the expression in 1924; → mean; → opacity.

A → spectroscopic phenomenon observed when either an → eclipsing binary's → secondary star or an → extrasolar planet is seen to → transit across the face of the → primary body. Because of the rotation of the star, an asymmetric distortion takes place in the → line profiles of the stellar spectrum, which changes during the transit. The measurement of this effect can be used to derive the → alignment of the → orbit of the transiting exoplanet with respect to the → rotation axis of the star.

Named after Richard Alfred Rossiter (1886-1977) and Dean Benjamin McLaughlin (1901-1965), American astronomers.

To turn around an axis. See also → revolve.

From L. rotare "to cause to spin, roll, move in a circle," from L. rota "wheel;" cognate with Pers. râh "way, path" (from Mid.Pers. râh, râs "way, street," also rah, ras "chariot;" from Proto-Iranian *rāθa-; cf. Av. raθa- "chariot;" Skt. rátha- "car, chariot," rathyā- "road;" Lith. ratas "wheel;" O.H.G. rad; Ger. Rad; Du. rad; O.Ir. roth; PIE *roto- "to run, to turn, to roll").

Carxidan "to rotate," from carx "every thing performing a circulatory motion; a wheel; a cart;" Mid.Pers. chr "wheel," Parthian cxr "wheel;" Ossetic calx "wheel;" Av. caxra- "wheel;" cognate with Skt. cakra- "wheel, circle; cycle," carati "he moves, wanders;" Gk. kyklos "circle, wheel," polos "axis of a sphere," polein "move around;" L. colere "to dwell in, to cultivate, move around," colonus "farmer, settler;" O.E. hweol "wheel;" Rus. koleso "wheel."

Capable of or having rotation.

From → rotate + → -ing.

A black hole that possesses angular momentum, as first postulated by Roy C. Kerr in 1963. Opposite of a stationary black hole. → ergosphere.

→ rotating; → black hole.

A star that has a non-zero → angular velocity. In a rotating star, the → centrifugal forces reduce the → effective gravity according to the latitude and also introduce deviations from sphericity. In a rotating star, the equations of stellar structure need to be modified. The usual spherical coordinates must be replaced by new coordinates characterizing the → equipotentials. See also → von Zeipel theorem.

→ rotating; → star.

The motion of a body about its axis.

Verbal noun of → rotate.

The imaginary line around which an object rotates. Same as → rotational axis and → axis of rotation.

→ rotation; → axis.