Rho Cassiopeiae (ρ Cas / ρ Cassiopeiae) is a yellow hypergiant in the constellation Cassiopeia. It is about 8150 light-years away, yet can still be seen by the naked eye (in the Northern Hemisphere only), as it is 550,000 times as luminous as the Sun. Its surface diameter is 450 times that of our sun's. On average, it has an absolute magnitude of −7.5, making it one of the most luminous stars known. In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... This article or section does not adequately cite its references or sources. ... Cassiopeia (IPA: ) is a northern constellation which Greek mythology considered to represent a vain queen who boasted about her unrivaled beauty. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (abbrev. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... 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. ... Semiregular variable stars are giants or supergiants of intermediate and late spectral type showing considerable periodicity in their light changes, accompanied or sometimes interrupted by various irregularities. ... 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 (from Old English gÄ“r) 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 (from Old English gÄ“r) 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 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). ... The globular cluster M80. ... A sphere rotating around its axis. ... STAR is an acronym for: Organizations Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... A year (from Old English gÄ“r) 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. ... The Henry Draper Catalogue is an astronomy catalogue with astrometric and spectroscopic data about more than 225,000 stars. ... Smithsonian Astrophysical Observatory Star Catalog contain the 258,996 stars. ... Fifth Fundamental Catalogue is a glossary of positions of stars. ... The Hipparcos and Tycho Catalogues (Tycho-1) are the primary products of the European Space Agencys astrometric mission, Hipparcos. ... SIMBAD (the Set of Identifications, Measurements, and Bibliography for Astronomical Data) is a database of astronomical information about objects within the Milky Way. ... Generally speaking, a yellow hypergiant is a very massive star with an extended chromosphere, which can be classified under the system as a spectral Class G, with a mass of up to approximately 120 solar masses (believed to be the upper limit of stellar mass). ... Cassiopeia (IPA: ) is a northern constellation which Greek mythology considered to represent a vain queen who boasted about her unrivaled beauty. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... The Northern Hemisphere is the half of a planets surface (or celestial sphere) that is north of the equator (the word hemisphere literally means half ball). On the Earth, the Northern Hemisphere contains most of the land and about 88-90% of the human population. ... Luminosity has different meanings in several different fields of science. ... The Sun is the star at the center of the Solar System. ... 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. ... Below is a list of stars in arranged in order of increasing absolute bolometric magnitude (decreasing luminosity). ...

Rho Cassiopeiae is somewhat unstable in its luminosity. Its normal magnitude is at about 4.5, but in 1946 it went down to 6th magnitude, before going back to normal. The same thing happened in 2000–2001, when it produced one of the largest outbursts known, ejecting 3% of a Solar-mass, the equivalent of 10,000 Earths. During the summer of 2000 it was observed (by the William Herschel Telescope) to have cooled from 7000 to 4000 degrees in the course of a few months. It seems to undergo these eruptions approximately once every 50 years (data suggests previous eruptions in 1893 and 1945). Instability in systems is generally characterized by some of the outputs or internal states growing without bounds. ... Luminosity has different meanings in several different fields of science. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... 1946 (MCMXLVI) was a common year starting on Tuesday. ... 2000 (MM) was a leap year starting on Saturday of the Gregorian calendar. ... 2001 (MMI) was a common year starting on Monday of the Gregorian calendar. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... This article is about the telescope on the Canary Islands. ...

Astronomers think Rho Cassiopeiae may go supernova in the near future because it will soon have consumed most of its nuclear fuel. Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ...

External links

• Press release from the William Herschel Telescope team about their findings.
• Rho Cassiopeiae fact sheet
• David Darling site