Eta Ophiuchi (η Oph / η Ophiuchi) is a star in the constellation Ophiuchus. It also has the traditional name Sabik The Great. In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... This article or section does not cite its references or sources. ... Ophiuchus is one of the 88 constellations, and was also one of the 48 listed by Ptolemy. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (dec) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. ... // 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. ... This article does not cite its references or sources. ... 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 article or section does not cite its references or sources. ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... Distance is a numerical description of how far apart things lie. ... A light-year or lightyear, symbol ly, is 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? Mass is a 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. ... In classical geometry, a radius 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 zero—the lowest possible temperature where nothing could be colder and no heat energy remains in a substance—is defined as zero kelvin (0 K). ... In astronomy, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. ... A sphere rotating around its axis. ... The Pleiades, an open cluster of stars in the constellation of Taurus. ... 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. ... The Henry Draper Catalogue is an astronomy catalogue with astrometric and spectroscopic data about more than 225,000 stars. ... The Bright Star Catalogue, also known as the Yale Catalogue of Bright Stars or Yale Bright Star Catalogue, is a star catalogue that lists of all stars of stellar magnitude 6. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In astronomy, many stars are referred to simply by catalogue numbers. ... The Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian Institution headquartered in Cambridge, Massachusetts, where it is joined with the Harvard College Observatory (HCO) to form the Harvard-Smithsonian Center for Astrophysics (CfA). ... In astronomy, many stars are referred to simply by catalogue numbers. ... SIMBAD (the Set of Identifications, Measurements, and Bibliography for Astronomical Data) is a database of astronomical information about objects within the Milky Way. ... The Pleiades, an open cluster of stars in the constellation of Taurus. ... This article or section does not cite its references or sources. ... Ophiuchus is one of the 88 constellations, and was also one of the 48 listed by Ptolemy. ...

η Oph is actually a binary star system that is difficult to resolve in amateur telescopes but whose true nature has been determined through use of more advanced techniques. The "primary" star (whose observational data make up the table in this article), which could nominally be referred to as η Oph A, is actually only slightly larger and warmer than its companion, η Oph B. Individually each star is a fairly unremarkable A class main sequence star, but as a binary pair they are unusual. Each star orbits around a common center in a very fast and highly elliptical orbit, making planetary formation impossible in this system and some stellar data imprecise. A binary system is an astronomy term referring to two objects in space, usually stars, which are so close that their gravitational forces attract one another into a mutual orbit. ... 50 cm refracting telescope at Nice Observatory. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... Artists impression of a binary system consisting of a black hole, with an accretion disc around it, and a main sequence star. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... The eight planets and three dwarf planets of the Solar System. ...