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82 G. Eridani
82 G. Eridani (HD 20794, Gliese 139, e Eridani) is a star away from Earth in the constellation Eridanus. It is a main-sequence star with a stellar classification of G6 V, and it hosts a system of three confirmed planets and a dust disk. Observation In the southern-sky catalog ''Uranometria Argentina'', 82 G. Eridani (often abbreviated to 82 Eridani) is the 82nd star listed in the constellation Eridanus. The Argentina catalog, compiled by the 19th-century astronomer Benjamin Gould, is a southern celestial hemisphere analog of the more famous Flamsteed catalog, and uses a similar numbering scheme. 82 G. Eridani, like other stars near the Sun, has held on to its Gould designation, even while other more distant stars have not. Properties 82 G. Eridani is slightly smaller and less massive than the Sun, at around 80% of the Sun's mass and 90% of the radius. It has a luminosity 30% fainter than the Sun's. Spectroscopically, it is classified as G6V, compared to G2V fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eridanus (constellation)
Eridanus is a constellation which stretches along the southern celestial hemisphere. It is represented as a river. One of the 48 constellations listed by the 2nd century AD astronomer Ptolemy, it remains one of the 88 modern constellations. It is the List of constellations by area, sixth largest of the modern constellations. The same name was later taken as a Latin name for the real Po River and also for the name of a Eridanos (Athens), minor river in Athens. Features Stars At its southern end is the apparent magnitude, magnitude 0.5 star Achernar, designated Alpha Eridani. It is a blue-white hued main sequence star 144 light-years from Earth, whose traditional name means "the river's end". Achernar is a very peculiar star because it is one of the flattest stars known. Observations indicate that its radius is about 50% larger at the equator than at the poles. This distortion occurs because the star is spinning extremely rapidly. There are several other noteworthy stars in E ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Infrared Space Observatory
The Infrared Space Observatory (ISO) was a space telescope for infrared light designed and operated by the European Space Agency (ESA), in cooperation with ISAS (now part of Japan Aerospace Exploration Agency, JAXA) and National Aeronautics and Space Administration, NASA. The ISO was designed to study infrared light at wavelengths of 2.5 to 240 micrometres and operated from 1995 to 1998. The Euro, €480.1-million satellite was launched on 17 November 1995 from the Centre Spatial Guyanais#ELA-2, ELA-2 launch pad at the Guiana Space Centre near Kourou in French Guiana. The launch vehicle, an Ariane 44P rocket, placed ISO successfully into a Elliptic orbit, highly elliptical geocentric orbit, completing one revolution around the Earth (planet), Earth every 24 hours. The primary mirror of its Ritchey-Chrétien telescope measured 60 cm in diameter and was cooled to 1.7 kelvins by means of superfluid helium. The ISO satellite contained four instruments that allowed for imaging an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Terrestrial Planet
A terrestrial planet, tellurian planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate, rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Venus, Earth and Mars. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites – Earth's Moon, Io, and sometimes Europa – may also be considered terrestrial planets. The large rocky asteroids Pallas and Vesta are sometimes included as well, albeit rarely. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth (''Terra'' and ''Tellus''), as these planets are, in terms of structure, ''Earth-like''. Terrestrial planets are generally studied by geologists, astronomers, and geophysicists. Terrestrial planets have a solid planetary surface, making them substantially different from larger gaseous planets, which are composed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomy & Astrophysics
''Astronomy & Astrophysics (A&A)'' is a monthly peer-reviewed scientific journal covering theoretical, observational, and instrumental astronomy and astrophysics. It is operated by an editorial team under the supervision of a board of directors representing 27 sponsoring countries plus a representative of the European Southern Observatory. The journal is published by EDP Sciences and the current editors-in-chief are Thierry Forveille and João Alves. History Origins ''Astronomy & Astrophysics'' was created as an answer to the publishing situation found in Europe in the 1960s. At that time, multiple journals were being published in several countries around the continent. These journals usually had a limited number of subscribers, and articles were written in languages other than English. They were less widely read than American and British journals and the research they reported had therefore less impact in the community. Starting in 1963, conversations between astronomers from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxford University
The University of Oxford is a collegiate research university in Oxford, England. There is evidence of teaching as early as 1096, making it the oldest university in the English-speaking world and the second-oldest continuously operating university globally. It expanded rapidly from 1167, when Henry II prohibited English students from attending the University of Paris. When disputes erupted between students and the Oxford townspeople, some Oxford academics fled northeast to Cambridge, where they established the University of Cambridge in 1209. The two English ancient universities share many common features and are jointly referred to as ''Oxbridge''. The University of Oxford comprises 43 constituent colleges, consisting of 36 semi-autonomous colleges, four permanent private halls and three societies (colleges that are departments of the university, without their own royal charter). and a range of academic departments that are organised into four divisions. Each college ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
82 G
8 (eight) is the natural number following 7 and preceding 9. Etymology English ''eight'', from Old English '', æhta'', Proto-Germanic ''*ahto'' is a direct continuation of Proto-Indo-European '' *oḱtṓ(w)-'', and as such cognate with Greek and Latin , both of which stems are reflected by the English prefix oct(o)-, as in the ordinal adjective ''octaval'' or ''octavary'', the distributive adjective is ''octonary''. The adjective ''octuple'' (Latin ) may also be used as a noun, meaning "a set of eight items"; the diminutive ''octuplet'' is mostly used to refer to eight siblings delivered in one birth. The Semitic numeral is based on a root ''*θmn-'', whence Akkadian ''smn-'', Arabic ''ṯmn-'', Hebrew ''šmn-'' etc. The Chinese numeral, written (Mandarin: ''bā''; Cantonese: ''baat''), is from Old Chinese ''*priāt-'', ultimately from Sino-Tibetan ''b-r-gyat'' or ''b-g-ryat'' which also yielded Tibetan '' brgyat''. It has been argued that, as the cardinal num ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Habitable Zone
In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kasting, D. P. Whitmire, R. T. Reynolds, Icarus 101, 108 (1993). The bounds of the HZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun. Due to the importance of liquid water to Earth's biosphere, the nature of the HZ and the objects within it may be instrumental in determining the scope and distribution of planets capable of supporting Earth-like extraterrestrial life and extraterrestrial intelligence, intelligence. As such, it is considered by many to be a major factor of planetary habitability, and the most likely place to find extraterrestrial liquid water and biosignatures elsewhere in the universe. The habitable zone is also called the Goldilocks zone, a metaphor, all ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bond Albedo
The Bond albedo (also called spheric albedo, planetary albedo, and bolometric albedo), named after the American astronomer George Phillips Bond (1825–1865), who originally proposed it, is the fraction of power in the total electromagnetic radiation incident on an astronomical body that is scattered back out into space. Because the Bond albedo accounts for all of the light scattered from a body at all wavelengths and all phase angles, it is a necessary quantity for determining how much energy a body absorbs. This, in turn, is crucial for determining the equilibrium temperature of a body. Because bodies in the outer Solar System are always observed at very low phase angles from the Earth, the only reliable data for measuring their Bond albedo comes from spacecraft. Phase integral The Bond albedo (''A'') is related to the geometric albedo (''p'') by the expression :A = pq where ''q'' is termed the ''phase integral'' and is given in terms of the directional scattered flux '' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equilibrium Temperature
The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were in radiative equilibrium, typically under the assumption that it radiates as a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is irrelevant, as the equilibrium temperature is calculated purely from a balance with incident stellar energy. Other authors use different names for this concept, such as equivalent blackbody temperature of a planet. The effective radiation emission temperature is a related concept, but focuses on the actual power radiated rather than on the power being received, and so may have a different value if the planet has an internal energy source or when the planet is not in radiative equilibrium. Planetary equilibrium temperature differs from the global mean temperature and surface air temperature, which are measured observationally by satellites or surface-based i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radial Velocity
The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity onto the relative direction or line-of-sight (LOS) connecting the two points. The radial speed or range rate is the temporal rate of the distance or range between the two points. It is a signed scalar quantity, formulated as the scalar projection of the relative velocity vector onto the LOS direction. Equivalently, radial speed equals the norm of the radial velocity, modulo the sign. In astronomy, the point is usually taken to be the observer on Earth, so the radial velocity then denotes the speed with which the object moves away from the Earth (or approaches it, for a negative radial velocity). Formulation Given a differentiable vector \mathbf r \in \mathbb^3 defining the instantaneous relative position of a target with respe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Super-Earth
A super-Earth is a type of exoplanet with a mass higher than Earth, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17.1 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or Planetary habitability, habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term. Definition In general, super-Earths are defined by their masses. The term does not imply temperatures, compositions, orbital properties, habitability, or environments. While sources generally agree on an upper bound of 10 Earth masses (~69% of the mass of Uranus, which is the Solar System's giant planet with the least mass), the lower bound varies from 1 or 1.9 to 5, with various other definitions appearing in the popular media. The term "super-Earth" is also used ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
