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Gamma Arae
Gamma Arae
Gamma Arae
(γ Ara, γ Arae) is a star in the southern constellation of Ara. With an apparent visual magnitude of 3.3,[2] it is the fourth-brightest star in the constellation and is readily visible to the naked eye. From parallax measurements made during the Hipparcos mission, the distance to this star can be estimated as 1,110 light-years (340 parsecs) from Earth. This is an enormous star with 23[7] times the radius of the Sun. It is radiating 120,000[5] as much energy as the Sun
Sun
from its outer envelope at an effective temperature of 21,500 K.[8] This heat gives the star the blue-white glow of a B-type star
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Epoch (astronomy)
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time.[1] These time-varying astronomical quantities might include, for example, the mean longitude or mean anomaly of a body, the node of its orbit relative to a reference plane, the direction of the apogee or aphelion of its orbit, or the size of the major axis of its orbit. The main use of astronomical quantities specified in this way is to calculate other relevant parameters of motion, in order to predict future positions and velocities
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Harvard Revised Catalogue
The Bright Star Catalogue, also known as the Yale Catalogue of Bright Stars or Yale Bright Star Catalogue, is a star catalogue that lists all stars of stellar magnitude 6.5 or brighter, which is roughly every star visible to the naked eye from Earth. The catalog contains 9,110 objects, of which 9,095 are stars, 11 are novae or supernovae,[1] and 4 are non-stellar objects; the non-stellar objects are the globular clusters 47 Tucanae
47 Tucanae
(designated HR 95) and NGC 2808
NGC 2808
(HR 3671), and the open clusters NGC 2281
NGC 2281
(HR 2496) and Messier 67
Messier 67
(HR 3515).[2] The catalogue is fixed in number of entries, but its data is maintained, and it is appended with a comments section about the objects that has been steadily enhanced since the Yale astronomer Frank Schlesinger
Frank Schlesinger
published the first version in 1930
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Kelvin
The Kelvin
Kelvin
scale is an absolute thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin (symbol: K) is the base unit of temperature in the International System of Units
International System of Units
(SI). The kelvin is defined as the fraction ​1⁄273.16 of the thermodynamic temperature of the triple point of water (exactly 0.01 °C or 32.018 °F).[1] In other words, it is defined such that the triple point of water is exactly 273.16 K. The Kelvin
Kelvin
scale is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907), who wrote of the need for an "absolute thermometric scale". Unlike the degree Fahrenheit
Fahrenheit
and degree Celsius, the kelvin is not referred to or typeset as a degree
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Stellar Rotation
Stellar rotation
Stellar rotation
is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge due to centrifugal force. As stars are not solid bodies, they can also undergo differential rotation. Thus the equator of the star can rotate at a different angular velocity than the higher latitudes. These differences in the rate of rotation within a star may have a significant role in the generation of a stellar magnetic field.[1] The magnetic field of a star interacts with the stellar wind. As the wind moves away from the star its rate of angular velocity slows. The magnetic field of the star interacts with the wind, which applies a drag to the stellar rotation
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Projected Rotational Velocity
Stellar rotation
Stellar rotation
is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge due to centrifugal force. As stars are not solid bodies, they can also undergo differential rotation. Thus the equator of the star can rotate at a different angular velocity than the higher latitudes. These differences in the rate of rotation within a star may have a significant role in the generation of a stellar magnetic field.[1] The magnetic field of a star interacts with the stellar wind. As the wind moves away from the star its rate of angular velocity slows. The magnetic field of the star interacts with the wind, which applies a drag to the stellar rotation
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Stellar Evolution
Stellar evolution
Stellar evolution
is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the age of the universe. The table shows the lifetimes of stars as a function of their masses.[1] All stars are born from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star. Nuclear fusion
Nuclear fusion
powers a star for most of its life. Initially the energy is generated by the fusion of hydrogen atoms at the core of the main-sequence star
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Megayear
A year is the orbital period of the Earth
Earth
moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the planet, four seasons are generally recognized: spring, summer, autumn and winter. In tropical and subtropical regions several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked. The current year is 2018. A calendar year is an approximation of the number of days of the Earth's orbital period as counted in a given calendar. The Gregorian, or modern, calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars; see below
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Star Catalogue
A star catalogue (Commonwealth English) or star catalog (American English), is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some of the more frequently quoted ones. Star
Star
catalogues were compiled by many different ancient peoples, including the Babylonians, Greeks, Chinese, Persians, and Arabs
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Cape Photographic Durchmusterung
In astronomy, Durchmusterung or Bonner Durchmusterung (BD), is the comprehensive astrometric star catalogue of the whole sky, compiled by the Bonn
Bonn
Observatory
Observatory
(Germany) from 1859 to 1903.[1] The name comes from Durchmusterung ("run-through examination"), a German word used for a systematic survey of objects or data. The term has sometimes been used for other astronomical surveys, including not only stars but also the search for other celestial objects
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Henry Draper Catalogue
The Henry Draper
Henry Draper
Catalogue (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper
Henry Draper
Extension (HDE), published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the Henry Draper
Henry Draper
Extension Charts (HDEC), published from 1937 to 1949 in the form of charts, which gave classifications for 86,933 more stars
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Hipparcos Catalogue
Hipparcos
Hipparcos
was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky.[3] This permitted the accurate determination of proper motions and parallaxes of stars, allowing a determination of their distance and tangential velocity. When combined with radial velocity measurements from spectroscopy, this pinpointed all six quantities needed to determine the motion of stars. The resulting Hipparcos
Hipparcos
Catalogue, a high-precision catalogue of more than 118,200 stars, was published in 1997. The lower-precision Tycho Catalogue of more than a million stars was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000
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Smithsonian Astrophysical Observatory Star Catalog
The Smithsonian Astrophysical Observatory
Smithsonian Astrophysical Observatory
Star Catalog is an astrometric star catalogue. It was published by the Smithsonian Astrophysical Observatory in 1966 and contains 258,997 stars.[1][2][3][4] The catalogue was compiled from various previous astrometric catalogues, and contains only stars to about ninth magnitude for which accurate proper motions were known. Names in the SAO catalogue start with the letters SAO, followed by a number
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Centimetre–gram–second System Of Units
The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways of extending the CGS system to cover electromagnetism.[1][2] The CGS system has been largely supplanted by the MKS system based on the metre, kilogram, and second, which was in turn extended and replaced by the International System of Units
International System of Units
(SI)
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Einstein Observatory
Einstein Observatory
Einstein Observatory
(HEAO-2) was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories. Named HEAO B before launch, the observatory's name was changed to honor Albert Einstein
Albert Einstein
upon its successfully attaining orbit.[1]Contents1 Launch 2 Instrumentation 3 References 4 See also 5 External linksLaunch[edit] The Einstein Observatory, HEAO-2, was launched on November 13, 1978, from Cape Canaveral, Florida, on an Atlas-Centaur
Atlas-Centaur
SLV-3D booster rocket into a near-circular orbit with an initial altitude slightly above 500 km. Its orbital inclination orbit was 23.5 degrees
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SIMBAD
SIMBAD
SIMBAD
(the Set of Identifications, Measurements, and Bibliography for Astronomical Data) is an astronomical database of objects beyond the Solar System. It is maintained by the Centre de données astronomiques de Strasbourg (CDS), France. SIMBAD
SIMBAD
was created by merging the Catalog of Stellar Identifications (CSI) and the Bibliographic Star Index as they existed at the Meudon Computer Centre until 1979, and then expanded by additional source data from other catalogues and the academic literature. The first on-line interactive version, known as Version 2, was made available in 1981. Version 3, developed in the C language and running on UNIX stations at the Strasbourg Observatory, was released in 1990
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