NationMaster - Encyclopedia: Gliese 876

Gliese 876 is a red dwarf star located approximately 15 light-years away in the constellation Aquarius. It has the variable star designation IL Aquarii. As of 2006 the star is known to host three extrasolar planets, including one with a mass less than half that of Neptune. In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... It has been suggested that this article or section be merged into Julian epoch. ... This article or section does not adequately cite its references or sources. ... Aquarius (IPA: , Latin: ) is the eleventh sign of the zodiac, situated between Capricornus and Pisces. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (abbrev. ... // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. ... In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. ... Most stars are of almost constant luminosity. ... BY Draconis variables are main sequence variable stars of late spectral types, usually K or M. They exhibit variations in their luminosity due to rotation of the star coupled with star spots, and other chromospheric activity. ... Illustration of the use of optical wavelength interferometry to determine precise positions of stars. ... Radial velocity is the velocity of an object in the direction of the line of sight. ... kilometre per second is an SI derived unit of both speed (scalar) and velocity (vector), signified by the symbol km/s or km s-1. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... This does not adequately cite its references or sources. ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... Distance is a numerical description of how far apart objects are at any given moment in time. ... A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in vacuum in one Julian year. ... Stellar parallax motion The parsec (symbol pc) is a unit of length used in astronomy. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... Circle illustration In classical geometry, a radius (plural: radii) of a circle or sphere is any line segment from its center to its boundary. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... Luminosity has different meanings in several different fields of science. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... Fig. ... The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zeroâ€”the lowest possible temperature where nothing could be colder and no heat energy remains in a substanceâ€”is defined as zero kelvin (0 K). ... The globular cluster M80. ... A sphere rotating around its axis. ... Look up day in Wiktionary, the free dictionary. ... STAR is an acronym for: Organizations Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... Alexander N. Vyssotsky (born May 23, 1888 in Moscow, Russia; died December 31, 1973 in Winter Park, Florida) was an astronomer. ... The Hipparcos and Tycho Catalogues (Tycho-1) are the primary products of the European Space Agencys astrometric mission, Hipparcos. ... An artists impression of a planet in orbit around a red dwarf According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type. ... STAR is an acronym for: Organizations Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... This article or section does not adequately cite its references or sources. ... Aquarius (IPA: , Latin: ) is the eleventh sign of the zodiac, situated between Capricornus and Pisces. ... Most stars are of almost constant luminosity. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ... An extrasolar planet, or exoplanet, is a planet beyond the Solar System. ... Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... Adjectives: Neptunian Atmosphere Surface pressure: (?)â‰«(?) 100 kPa : is asked the pressure at the cloud level. ...

Distance and visibility

Gliese 876 is located fairly close to our solar system. According to astrometric measurements made by the Hipparcos satellite, the star shows a parallax of 212.59 milliarcseconds,^[1] which corresponds to a distance of 4.70 parsecs (15.3 light years). Despite being located so close to us, the star is so faint that it is invisible to the naked eye and can only be seen using a telescope. Major features of the Solar System (not to scale; from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth and its Moon, and Mars. ... Illustration of the use of optical wavelength interferometry to determine precise positions of stars. ... Hipparcos (for High Precision Parallax Collecting Satellite) was an astrometry mission of the European Space Agency (ESA) dedicated to the measurement of stellar parallax and the proper motions of stars. ... An Earth observation satellite, ERS 2 For other uses, see Satellite (disambiguation). ... This does not adequately cite its references or sources. ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... Stellar parallax motion The parsec (symbol pc) is a unit of length used in astronomy. ... A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in vacuum in one Julian year. ... The naked eye is a figure of speech referring to human visual perception that is unaided by enhancing equipment, such as a telescope or binoculars. ... A telescope (from the Greek tele = far and skopein = to look or see; teleskopos = far-seeing) is an instrument designed for the observation of remote objects. ...

Stellar characteristics

As a red dwarf star, Gliese 876 is much less massive than our Sun: estimates suggest it has only 32% of the mass of our local star.^[2] The surface temperature of Gliese 876 is cooler than our Sun and the star has a smaller radius.^[3] These factors combine to make the star only 1.24% as luminous as the Sun, though most of this is at infrared wavelengths. Fig. ... Luminosity has different meanings in several different fields of science. ... Image of two girls in mid-infrared (thermal) light (false-color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ... The wavelength is the distance between repeating units of a wave pattern. ...

Estimating the age and metallicity of cool stars is difficult due to the formation of diatomic molecules in their atmospheres, which makes the spectrum extremely complex. By fitting the observed spectrum to model spectra, it is estimated that Gliese 876 has a slightly lower abundance of heavy elements compared to the Sun (around 75% the solar abundance of iron).^[4] Based on chromospheric activity the star is likely to be around 6,520 or 9,900 million years old, depending on the theoretical model used.^[5] In astronomy and cosmology, the term metal or metal-rich is used to refer to any element heavier than hydrogen and helium. ... Diatomic molecules are molecules formed of two atoms of the same element. ... View of Jupiters active atmosphere, including the Great Red Spot. ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... The chromosphere (literally, color sphere) is a thin layer of the Suns atmosphere just above the photosphere, roughly 10,000 kilometers deep. ...

Like many low-mass stars, Gliese 876 is a variable star. It is classified as a BY Draconis variable and its brightness fluctuates by around 0.04 magnitudes.^[6] This type of variability is thought to be caused by large starspots moving in and out of view as the star rotates.^[7] BY Draconis variables are main sequence variable stars of late spectral types, usually K or M. They exhibit variations in their luminosity due to rotation of the star coupled with star spots, and other chromospheric activity. ... // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ... 400 year sunspot history A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. ...

Appearance in Novel

Gliese 876 features in the book The Camels Sandbox The Camels Sandbox The Camels Sandbox is a fictional novel written by Kanji Sakayama in 1979. ...

Planetary system

In 1998 an extrasolar planet was announced in orbit around Gliese 876 by two independent teams led by Geoffrey Marcy^[2] and Xavier Delfosse.^[8] The planet was designated Gliese 876 b and was detected by making measurements of the star's radial velocity as the planet's gravity pulled it around. The planet, around twice the mass of Jupiter, revolves around its star in an orbit taking approximately 61 days to complete, at a distance of only 0.208 AU, less than the distance from the Sun to Mercury.^[9] Image File history File links Download high resolution version (4000x3000, 4982 KB) Summary Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high resolution version (4000x3000, 4982 KB) Summary Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Gliese 876 b is an extrasolar planet orbiting the red dwarf star Gliese 876 every 60. ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean [1]. // Coated in ice, power and telephone lines sag and often break, resulting in power outages. ... m. ... Image:Geoff marcy. ... Gliese 876 b is an extrasolar planet orbiting the red dwarf star Gliese 876 every 60. ... Radial velocity is the velocity of an object in the direction of the line of sight. ... Gravity is a force of attraction that acts between bodies that have mass. ... Adjectives: Jovian Atmosphere Surface pressure: 20â€“200 kPa[4] (cloud layer) Composition: ~86% H2 ~13% Helium 0. ... Look up day in Wiktionary, the free dictionary. ... The astronomical unit (AU or au or a. ... This article is about planet. ...

In 2001 a second planet was detected in the system, inside the orbit of the previously-discovered planet.^[10] The 0.62 Jupiter-mass planet, designated Gliese 876 c is in a 2:1 orbital resonance with the outer planet, taking 30.340 days to orbit the star. This relationship between the orbital periods initially disguised the planet's radial velocity signature as an increased orbital eccentricity of the outer planet. The two planets undergo strong gravitational interactions as they orbit the star, causing the orbital elements to change rapidly.^[11] 2001 (MMI) was a common year starting on Monday of the Gregorian calendar. ... Gliese 876 c is an extrasolar planet orbiting the red dwarf star Gliese 876, taking 30. ... In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... The elements of an orbit are the parameters needed to specify that orbit uniquely, given a model of two ideal masses obeying the Newtonian laws of motion and the inverse-square law of gravitational attraction. ...

In 2005, further observations by a team led by Eugenio Rivera revealed a third planet in the system, inside the orbits of the two Jupiter-size planets.^[12] The planet, designated Gliese 876 d, has a minimum mass only 5.88 times that of the Earth and may be a terrestrial planet. Based on the radial velocity measurements and modelling the interactions between the two giant planets, the system's inclination is estimated to be around 50° to the plane of the sky. If this is the case and the system is assumed to be coplanar, the planetary masses are around 30% greater than the lower limits established by the radial velocity method. This would make the inner planet have a true mass around 7.5 times that of Earth. On the other hand, astrometric methods suggest an inclination around 84° for the outermost planet, which would mean the true masses are only slightly greater than the lower limit.^[13]. Another investigation led by Paul Shankland (which included Rivera and others), reveals a lack of any astronomical transits of the planets across the face of the star -- along with a radial velocity 'tilt' away from 90° (caused by the Rossiter-McLaughlin effect) -- and so indicates the notional ~90° inclination is further unlikely.^[14] 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... Gliese 876 d is an extrasolar planet orbiting the red dwarf star Gliese 876. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... The inner planets, their sizes to scale. ... Metroplex (in shadow) and Giant Planet Gigantion, or Giant Planet, is a fictional planet home to giant Transformers in the animated television program, Transformers: Cybertron; it is referred to as Gigalonia in Transformers: Galaxy Force, the Japanese version of the show. ... Inclination in general is the angle between a reference plane and another plane or axis of direction. ... In geometry, a set of points in space is coplanar if the points all lie in a geometric plane. ... 2003 Transit of Mercury The term transit or astronomical transit has two meanings in astronomy: A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, as seen by an observer at some particular vantage point. ... The Rossiter-McLaughlin effect is an spectroscopic phenomenon seen when either an eclipsing binarys secondary star or an extrasolar planet is seen to transit across the face of the primary or parent star. ...

Both of the system's Jupiter-mass planets are located in the 'traditional' habitable zone (HZ) of Gliese 876, which extends between 0.116 to 0.227 AU from the star.^[15] Unless a notional planet is tidally locked outside this region, this leaves little room for an additional habitable Earth-size planet in the system. On the other hand, large moons of the gas giants, if they exist, may be able to support life, as well as those planets or moons which may be tidally locked (further from the parent star's HZ) to provide a habitable terminator strip, as Joshi's team desscribes.^[16]. In astronomy a habitable zone (HZ) is a region of space where conditions are favorable for life. ... Understanding planetary habitability is partly an extrapolation of the Earths conditions, as it is the only planet currently known to support life. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... For other uses, see Life (disambiguation). ... A separate article treats the phenomenon of tidal resonance in oceanography. ...

Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Look up day in Wiktionary, the free dictionary. ... The astronomical unit (AU or au or a. ... Gliese 876 d is an extrasolar planet orbiting the red dwarf star Gliese 876. ... Gliese 876 c is an extrasolar planet orbiting the red dwarf star Gliese 876, taking 30. ... Gliese 876 b is an extrasolar planet orbiting the red dwarf star Gliese 876 every 60. ...

Contents

Distance and visibility

Stellar characteristics

Appearance in Novel

Planetary system

See also

References

External links

Contents

Distance and visibility GA_googleFillSlot("encyclopedia_square");

Stellar characteristics

Appearance in Novel

Planetary system

See also

References

External links

Distance and visibility