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Iota Boötis
Iota Boötis is a wide binary star system in the constellation Boötes, approximately 96 light-years from Earth. Its name is a Bayer designation that is Romanization of Greek, Latinized from ι Boötis, and abbreviated Iota Boo or ι Boo. The brighter component has the traditional name Asellus Secundus, pronounced , which is Latin for "second donkey colt", and the Flamsteed designation 21 Boötis. It is faintly visible to the naked eye with a typical apparent visual magnitude of +4.75. Based on stellar parallax, parallax measurements, it is located at a distance of from the Earth. The star is drifting closer to the Sun with a radial velocity of −19 km/s. The companion is HD 234121, a K-type main-sequence star at an angular distance of 38.6 arcseconds; easily separated with binoculars. Components The primary component is a white hued A-type main-sequence star with a stellar classification of A7V. It is classified as a Delta Scuti variable, Delta Scuti-type varia ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boötes
Boötes ( ) is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere. The name comes from , which comes from 'herder, herdsman' or 'plowman' (literally, 'ox-driver'; from ''boûs'' 'cow'). One of the 48 constellations described by the 2nd-century astronomer Ptolemy, Boötes is now one of the 88 modern constellations. It contains the List of brightest stars, fourth-brightest star in the night sky, the orange giant Arcturus. Epsilon Boötis, or Izar, is a colourful multiple star popular with amateur astronomers. Boötes is home to many other bright stars, including eight above the fourth magnitude and an additional 21 above the fifth magnitude, making a total of 29 stars easily visible to the naked eye. History and mythology In ancient Babylon, the stars of Boötes were known as SHU.PA. They were apparently depicted as the god Enlil, who was the leader of the Babylonian religion, Babyloni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arcseconds
A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a turn. The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth, so the actual Earth's circumference is very near . A minute of arc is of a radian. A second of arc, arcsecond (abbreviated as arcsec), or arc second, denoted by the symbol , is a unit of angular measurement equal to of a minute of arc, of a degree, of a turn, and (about ) of a radian. These units originated in Babylonian astronomy as sexagesimal (base 60) subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy, optometry, ophthalmology, optics, navigation, land surveying, and marksmanship. To express even smaller angles, standard SI prefixes can be employed; the milliarcsec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
κ Boo
Kappa (; uppercase Κ, lowercase κ or cursive ; , ''káppa'') is the tenth letter of the Greek alphabet, representing the voiceless velar plosive sound in Ancient and Modern Greek. In the system of Greek numerals, has a value of 20. It was derived from the Phoenician letter kaph . Letters that arose from kappa include the Roman K and Cyrillic К. The uppercase form is identical to the Latin K. Greek proper names and placenames containing kappa are often written in English with "c" due to the Romans' transliterations into the Latin alphabet: Constantinople, Corinth, Crete. All formal modern romanizations of Greek now use the letter "k", however. The cursive form is generally a simple font variant of lower-case kappa, but it is encoded separately in Unicode for occasions where it is used as a separate symbol in math and science. In mathematics, the kappa curve is named after this letter; the tangents of this curve were first calculated by Isaac Barrow in the 17th century. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
θ Boo
Theta (, ) uppercase Θ or ; lowercase θ or ; ''thē̂ta'' ; Modern: ''thī́ta'' ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth 𐤈. In the system of Greek numerals, it has a value of 9. Greek In Ancient Greek, θ represented the aspirated voiceless dental plosive , but in Modern Greek it represents the voiceless dental fricative . Forms In its archaic form, θ was written as a cross within a circle (as in the Etruscan or ), and later, as a line or point in circle ( or ). The cursive form was retained by Unicode as , separate from . (There is also .) For the purpose of writing Greek text, the two can be font variants of a single character, but are also used as distinct symbols in technical and mathematical contexts. Extensive lists of examples follow below at Mathematics and Science. is also common in biblical and theological usage e.g. instead of πρόθεσις (means placing in public or laying out a corpse). La ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Washington Double Star Catalog
The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of January 2024) 157,012 pairs of double stars. The catalog also includes multiple stars. In general, a multiple star with ''n'' components will be represented by entries in the catalog for ''n''−1 pairs of stars. History The database used to construct the WDS originated at Lick Observatory, where it was used to construct the Index Catalog of Visual Double Stars, published in 1963. In 1965, under the initiative of Charles Worley, it was transferred to the Naval Observatory. The catalog has since been augmented by many measurements, mainly from the Hipparcos and Tycho catalogues and results from speckle interferometry, as well as other sources. A unique 1–3 letter discovery code is used to identify the observer who reported the information. For example ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Projected Separation
This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outside the atmosphere of Earth. The field of astronomy features an extensive vocabulary and a significant amount of jargon. A B C D E F G H I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectral Class
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The ''spectral class'' of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are currently classified under the Morgan–Keenan (MK) system using the letters ''O'', ''B'', ''A'', ''F'', ''G'', ''K'', and ''M'', a sequence from the hottest (''O'' type) to the coolest (''M'' type). Each letter class is then subdivided ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Common Proper Motion
This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of astronomical object, celestial objects and phenomena that originate outside the atmosphere of Earth. The field of astronomy features an extensive vocabulary and a significant amount of jargon. A B C D E F G H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Effective Temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature when the body's emissivity curve (as a function of wavelength) is not known. When the star's or planet's net emissivity in the relevant wavelength band is less than unity (less than that of a black body), the actual temperature of the body will be higher than the effective temperature. The net emissivity may be low due to surface or atmospheric properties, such as the greenhouse effect. Star The effective temperature of a star is the temperature of a black body with the same luminosity per ''surface area'' () as the star and is defined according to the Stefan–Boltzmann law . Notice that the total ( bolometric) luminosity of a star is then , where is the stellar radius. The definition of the stellar radius is obviously not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosphere
The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will escape without being scattered. A photosphere is the region of a luminous object, usually a star, that is transparent to photons of certain wavelengths. Stars, except neutron stars, have no solid or liquid surface. Therefore, the photosphere is typically used to describe the Sun's or another star's visual surface. Etymology The term ''photosphere'' is derived from Ancient Greek roots, φῶς, φωτός/''phos'', ''photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it being a spherical surface that is perceived to emit light. Temperature The surface of a star is defined to have a temperature given by the effective temperature in the Stefan–Boltzmann law. Various stars have photospheres of vari ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Projected Rotational Velocity
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. In its turn, the magnetic field of a star interacts with the stellar wind. As the wind moves away from the star its angular speed decreases. The magnetic field of the star interacts with the wind, which applies a drag to the stellar rotation. As a result, angular momentum is transferred from the star to the wind, and over time this gradually slows the star's rate of rotation. Measurement Unless a sta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Variable Star
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either: * ''Intrinsic variables'', whose luminosity actually changes periodically; for example, because the star swells and shrinks. * ''Extrinsic variables'', whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star has an orbiting companion that sometimes eclipses it. Many, possibly most, stars exhibit at least some oscillation in luminosity: the energy output of the Sun, for example, varies by about 0.1% over an 11-year solar cycle. Discovery An ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol. A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
