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78 Ursae Majoris
78 Ursae Majoris is a binary star system in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye as a faint point of light with a combined apparent visual magnitude of 4.93. Parallax estimates by Hipparcos put it at a distance of , but it is drifting closer with a radial velocity of −5 km/s. The system is a candidate member of the Ursa Major Moving Group. The binary nature of this system was announced by S. W. Burnham in 1894. The pair orbit each other with a period of 105 years and an eccentricity of 0.39. Their semimajor axis has an angular size of and the orbital plane is inclined by 47°. The primary member, designated component A, has a magnitude of 5.02 and is an F-type main-sequence star with a stellar classification of F2V. It is 785 million years old and is spinning with a projected rotational velocity of 92 km/s. The star has 1.34 times the mass of the Sun and is radiating 5.75 times the Sun's luminosi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
J2000
In astronomy, an epoch or reference epoch is a moment in time used as a reference point for some time-varying astronomical quantity. It is useful for the celestial coordinates or orbital elements of a celestial body, as they are subject to perturbations and vary with time. 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. The applied tools of the disciplines of celestial mechanics or its subfield orbital mechanics (for predicting orbital paths and positions for bodies in motion under the gravitational effects of other bodies) can be used to generate an ephemeris, a table of values giving ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stellar Classification
In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grating into a spectrum exhibiting the Continuum (spectrum), 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 cool ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Durchmusterung Objects
In astronomy, Durchmusterung or Bonner Durchmusterung (BD) is an astrometric star catalogue of the whole sky, published by the Bonn Observatory in Germany from 1859 to 1863, with an extension published in Bonn in 1886. The name comes from ('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. Special tasks include celestial scanning in electromagnetic spectrum, electromagnetic wavelengths shorter or longer than visible light waves. Original catalog The Bonner Durchmusterung (abbreviated BD), was initiated by Friedrich Wilhelm Argelander, Friedrich Argelander and using observations largely carried out by his assistants, which resulted in a catalogue of the positions and apparent magnitudes of 342,198 stars down to approximate apparent magnitude 9.5 and covering the sky from 90°N to 2°S declination. The cat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ursa Major
Ursa Major, also known as the Great Bear, is a constellation in the Northern Sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear", referring to and contrasting it with nearby Ursa Minor, the lesser bear. In antiquity, it was one of the original 48 constellations listed by Ptolemy in the 2nd century AD, drawing on earlier works by Greek, Egyptian, Babylonian, and Assyrian astronomers. Today it is the third largest of the 88 modern constellations. Ursa Major is primarily known from the asterism of its main seven stars, which has been called the "Big Dipper", "the Wagon", "Charles's Wain", or "the Plough", among other names. In particular, the Big Dipper's stellar configuration mimics the shape of the " Little Dipper". Two of its stars, named Dubhe and Merak ( α Ursae Majoris and β Ursae Majoris), can be used as the navigational pointer towards the place of the current northern pole star, Polaris in Ursa Mino ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ursa Major Moving Group
The Ursa Major Moving Group, also known as Collinder 285 and the Ursa Major association, is the closest Stellar kinematics#Moving groups, stellar moving group – a set of stars with common velocities in space and thought to have a common origin in space and time. In the case of the Ursa Major group, all the stars formed about 300 million years ago. Its core is located roughly 80 light years away and part of the Local Bubble. It is rich in bright stars including most of the stars of the Big Dipper. Discovery and constituents All stars in the Ursa Major Moving Group are moving in roughly the same direction at similar velocities, and also have similar chemical compositions and estimated ages. This evidence suggests to astronomers that the stars in the group share a common origin. Based on the numbers of its constituent stars, the Ursa Major Moving Group is believed to have once been an open cluster, having formed from a protostellar nebula approximately 500 million years ag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Binary Stars
A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars using a telescope, in which case they are called ''visual binaries''. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy (''spectroscopic binaries'') or astrometry (''astrometric binaries''). If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other; these pairs are called ''eclipsing binaries'', or, together with other binaries that change brightness as they orbit, ''photometric binaries''. If components in binary star systems are close enough, they can gravitationally distort each other's outer stellar atmospheres. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
G-type Main-sequence Stars
A G-type main-sequence star (spectral type: G-V), also often, and imprecisely, called a yellow dwarf, or G star, is a main sequence, main-sequence star (luminosity class V) of stellar classification, spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about . Like other main-sequence stars, a G-type main-sequence star converts the Chemical element, element hydrogen to helium in its core by means of nuclear fusion. The Sun, the star in the center of the Solar System to which the Earth is gravitationally bound, is an example of a G-type main-sequence star (G2V type). Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton–proton chain (4 hydrogens form 1 helium), Mass–energy equivalence, converting about 4 million tons of matter to energy. Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri, Tau Ceti, and 51 Pegasi. Description Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
F-type Main-sequence Stars
An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VII and VIII. This temperature range gives the F-type stars a whitish hue when observed by the atmosphere. Because a main-sequence star is referred to as a dwarf star, this class of star may also be termed a yellow-white dwarf (not to be confused with white dwarfs, remnant stars that are a possible final stage of stellar evolution). Notable examples include Procyon A, Gamma Virginis A and B, and KIC 8462852. Spectral standard stars The revised Yerkes Atlas system (Johnson & Morgan 1953) listed a dense grid of F-type dwarf spectral standard stars; however, not all of these have survived to this day as stable standards. The ''anchor points'' of the MK spectral classification system among the F-type main-sequence dwarf stars, i.e. thos ... [...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] |
G-type Main-sequence Star
A G-type main-sequence star (spectral type: G-V), also often, and imprecisely, called a yellow dwarf, or G star, is a main sequence, main-sequence star (luminosity class V) of stellar classification, spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about . Like other main-sequence stars, a G-type main-sequence star converts the Chemical element, element hydrogen to helium in its core by means of nuclear fusion. The Sun, the star in the center of the Solar System to which the Earth is gravitationally bound, is an example of a G-type main-sequence star (G2V type). Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton–proton chain (4 hydrogens form 1 helium), Mass–energy equivalence, converting about 4 million tons of matter to energy. Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri, Tau Ceti, and 51 Pegasi. Description Th ... [...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] |
