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Beta Ursae Majoris
Merak , also called Beta Ursae Majoris (β Ursae Majoris, abbreviated Beta UMa, β UMa), is a star in the northern constellation of Ursa Major. The apparent visual magnitude of this star is +2.37, which means it is readily visible to the naked eye. It is more familiar to northern hemisphere observers as one of the "pointer stars" in the Big Dipper, or the Plough (UK), which is a prominent asterism of seven stars that forms part of the larger constellation. Extending an imaginary straight line from this star through the nearby Alpha Ursae Majoris (Dubhe) extends to Polaris, the north star. Spectral classification In 1943, β Ursae Majoris was listed as a spectral standard for the class of A1 V. When improved instruments made it possible to identify subgiant luminosity classes for early A-class stars, β Ursae Majoris was assigned that class A0 IV. This was later revised to A1 IV. It is considered to be a mild Am star, a type of chemically ... [...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] |
Alpha Ursae Majoris
Dubhe is a multiple star system in the northern constellation of Ursa Major. It is formally designated Alpha Ursae Majoris, Latinisation of names, Latinised from α Ursae Majoris, Despite being designated "α" (alpha), it is the second-brightest object in the constellation. Alpha Ursae Majoris is the northern of the 'pointers' (or 'guards'), the second being Beta Ursae Majoris, or 'Merak' – this pair of stars point towards Polaris, the North Star. α Ursae Majoris is located at a distance of approximately 123 light years from the Sun, based on stellar parallax, parallax measurements. Although it is part of the constellation of Ursa Major, it is not part of the Ursa Major Moving Group of stars that have a common motion through space. Components Dubhe is a spectroscopic binary made up of the stars ''α Ursae Majoris A'' and ''α Ursae Majoris B''. The pair orbit at a separation of about 23 astronomical units (AU), with a orbital period, period of 44.5 ye ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of red light (the longest waves in the visible spectrum), so IR is invisible to the human eye. IR is generally (according to ISO, CIE) understood to include wavelengths from around to . IR is commonly divided between longer-wavelength thermal IR, emitted from terrestrial sources, and shorter-wavelength IR or near-IR, part of the solar spectrum. Longer IR wavelengths (30–100 μm) are sometimes included as part of the terahertz radiation band. Almost all black-body radiation from objects near room temperature is in the IR band. As a form of EMR, IR carries energy and momentum, exerts radiation pressure, and has properties corresponding to both those of a wave and of a particle, the photon. It was long known that fires e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Luminosity
The solar luminosity () is a unit of radiant flux (Power (physics), power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxy, galaxies and other celestial objects in terms of the output of the Sun. One nominal solar luminosity is defined by the International Astronomical Union to be . This corresponds almost exactly to a bolometric magnitude, bolometric absolute magnitude of +4.74. The Sun is a weakly variable star, and its actual luminosity therefore Solar variation, fluctuates. The major fluctuation is the eleven-year solar cycle (sunspot cycle) that causes a quasi-periodic variation of about ±0.1%. Other variations over the last 200–300 years are thought to be much smaller than this. Determination Solar luminosity is related to Irradiance, solar irradiance (the solar constant). Slow changes in the axial tilt of the planet and the shape of its orbit cause cyclical changes to the solar irradiance. The result is orb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Radius
Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\times 10^8 \hbox is approximately 10 times the average radius of Jupiter, 109 times the radius of the Earth, and 1/215 of an astronomical unit, the approximate distance between Earth and the Sun. The solar radius to either pole and that to the equator differ slightly due to the Sun's rotation, which induces an oblateness in the order of 10 parts per million. Measurements The uncrewed SOHO spacecraft was used to measure the radius of the Sun by timing transits of Mercury across the surface during 2003 and 2006. The result was a measured radius of . Haberreiter, Schmutz & Kosovichev (2008) determined the radius corresponding to the solar photosphere to be . This new value is consistent with helioseismic estimates; the same study sho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Mass
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. More precisely, the mass of the Sun is The solar mass is about times the mass of Earth (), or times the mass of Jupiter (). History of measurement The value of the gravitational constant was first derived from measurements that were made by Henry Cavendish in 1798 with a torsion balance. The value he obtained differs by only 1% from the modern value, but was not as precise. The diurnal parallax of the Sun was accurately measured during the transits of Venus in 1761 and 1769, yielding a value of (9 arcseconds, compared to the present value of ). From the value of the diurnal parallax, one can determine the distance to the Sun from the geometry of Earth. The first known estimate of the solar mass was by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
A-type Star
A type or type A may refer to: Science * A-type asteroid, a type of relatively uncommon inner-belt asteroids * A type blood, a type in the ABO blood group system * A-type inclusion, a type of cell inclusion * A-type potassium channel, a type of voltage-gated potassium channel * A type proanthocyanidin, a specific type of flavonoids * A-type star, a class of stars * Type A climate, a type in the Köppen climate classification * Type A flu, a type of influenza virus * Type A evaluation of uncertainty, an uncertainty in measurement that can be inferred, for example, from repeated measurement * Type A personality, a personality type in the Type A and Type B personality theory * Hemophilia type A, a type of haemophilia * A-type granite a type of granite rock * Adenosine receptor The adenosine receptors (or P1 receptors) are a class of Purinergic receptor, purinergic G protein-coupled receptors with adenosine as the endogenous ligand (biochemistry), ligand. There are four kno ... [...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] |
Thermonuclear Fusion
Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutron by-products. The difference in mass between the reactants and products is manifested as either the release or absorption of energy. This difference in mass arises as a result of the difference in nuclear binding energy between the atomic nuclei before and after the fusion reaction. Nuclear fusion is the process that powers all active stars, via many reaction pathways. Fusion processes require an extremely large triple product of temperature, density, and confinement time. These conditions occur only in stellar cores, advanced nuclear weapons, and are approached in fusion power experiments. A nuclear fusion process that produces atomic nuclei lighter than nickel-62 is generally exothermic, due to the positive gradient of the nuclear binding energy curve. The most fusible nuclei are among the lightest, especially deuterium, tritium, and helium-3. The oppo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subgiant
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of a star. Yerkes luminosity class IV The term subgiant was first used in 1930 for class G and early K stars with absolute magnitudes between +2.5 and +4. These were noted as being part of a continuum of stars between obvious main-sequence stars such as the Sun and obvious giant stars such as Aldebaran, although less numerous than either the main sequence or the giant stars. The Yerkes spectral classification system is a two-dimensional scheme that uses a letter and number combination to denote the temperature of a star (e.g. A5 or M1) and a Roman numeral to indicate the luminosity relative to other stars of the same temperature. Luminosity class IV stars are the subgiants, located between main-sequence stars (luminosity class&n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphical), foreshortening, nearby objects show a larger parallax than farther objects, so parallax can be used to determine distances. To measure large distances, such as the distance of a planet or a star from Earth, astronomers use the principle of parallax. Here, the term ''Stellar parallax, parallax'' is the semi-angle of inclination between two sight-lines to the star, as observed when Earth is on opposite sides of the Sun in its orbit. These distances form the lowest rung of what is called "the cosmic distance ladder", the first in a succession of methods by which astronomers determine the distances to celestial objects, serving as a basis for other distance measurements in astronomy forming the higher rungs of the ladder. Because parallax ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemically Peculiar Star
In astrophysics, chemically peculiar stars (CP stars) are stars with distinctly unusual Metallicity, metal abundances, at least in their surface layers. Classification Chemically peculiar stars are common among hot main-sequence (hydrogen-burning) stars. These hot peculiar stars have been divided into four main classes on the basis of their spectra, although two classification systems are sometimes used: * non-magnetic metallic-lined star, metallic-lined (Am, CP1) * Ap and Bp stars, magnetic (Ap, CP2) * non-magnetic mercury-manganese star, mercury-manganese (HgMn, CP3) * Helium-weak star, helium-weak (He-weak, CP4). The class names provide a good idea of the peculiarities that set them apart from other stars on or near the main sequence. The Am stars (CP1 stars) show weak lines of singly ionized Calcium, Ca and/or Scandium, Sc, but show enhanced abundances of heavy metals. They also tend to be slow rotators and have an effective temperature between 7000 and . The Ap stars (CP2 st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
