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24 Ursae Majoris
24 Ursae Majoris is a variable star in the northern circumpolar constellation of Ursa Major, located 101.5 light-years from the Sun. It has the variable star designation DK Ursae Majoris and the Bayer designation d Ursae Majoris; ''24 Ursae Majoris'' is the Flamsteed designation. This object is visible to the naked eye as a faint, yellow-hued star with an apparent visual magnitude of 4.54. It is moving closer to the Earth with a heliocentric radial velocity of −27 km/s, and is expected to come as close as in around 879,000 years. Description 24 Ursae Majoris has a stellar classification of G4 III-IV, which, at the estimated age of about one billion years, matches the spectrum of an aging giant star blended with features of a subgiant luminosity class. Based upon its position on the H–R diagram, this star has just passed through the Hertzsprung gap and is ready to begin its first ascent along the red-giant branch. It is a suspected RS Canum Venati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
J2000
In astronomy, an epoch or reference epoch is a instant, 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 Astronomical object, celestial body, as they are subject to Perturbation (astronomy), 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 Perihelion and aphelion, 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 bodi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hertzsprung Gap
The Hertzsprung Gap is a feature of the Hertzsprung–Russell diagram for a star cluster. It is named after Ejnar Hertzsprung, who first noticed the absence of stars in the region of the Hertzsprung–Russell diagram between A5 and G0 spectral type and between +1 and −3 absolute magnitudes (i.e. between the top of the main sequence and the red giants for stars above roughly 1.5 solar mass). When a star during its evolution crosses the Hertzsprung gap, it means that it has finished core hydrogen burning. Stars do exist in the Hertzsprung gap region, but because they move through this section of the Hertzsprung–Russell diagram very quickly in comparison to the lifetime of the star (thousands of years, compared to tens of billions of years for the lifetime of the star), that portion of the diagram is less densely populated. Full Hertzsprung–Russell diagrams of the 11,000 Hipparcos mission targets show a handful of stars in that region.Binney, J. and Merrifield, M., "Galact ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rho Ursae Majoris
Rho Ursae Majoris (ρ UMa) is the Bayer designation for a solitary star in the northern circumpolar constellation of Ursa Major. It is faintly visible to the naked eye with an apparent visual magnitude of 4.74. The distance to this star, based upon an annual parallax shift of 10.37 mas, is around 315 light years. With a stellar classification of M3 III, this is a red giant star on the asymptotic giant branch. It is a suspected small amplitude variable. The measured angular diameter of the star after correcting for limb darkening is , which, at the estimated distance of this star, yields a physical size of about 58 times the radius of the Sun. It is radiating 464 times the solar luminosity from its outer atmosphere at an effective temperature of about 3,725 K. Based upon its motion through space, there is a 60.6% chance that this star is a member of the Sirius stream. Naming *With π1, π2, σ1, σ2, A and d, it composed the Arabic asteris ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sigma2 Ursae Majoris
Sigma2 Ursae Majoris (σ2 Ursae Majoris, σ2 UMa) is a binary star in the constellation of Ursa Major. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 66.5 light years (20.4 parsecs) from Earth, making this a fairly nearby system. The primary component has an apparent magnitude of about 4.8, meaning it can be seen with the naked eye ''(see Bortle scale)''. This is a visual binary, meaning that the two components can be resolved, and the orbit is derived from the positions of the two stars. The primary component Sigma2 Ursae Majoris A, is a white-colored F-type subgiant. Its radius is about 1.75 times that of the Sun, and it is 31% more massive. The companion is an orange K-type main-sequence star that is much fainter. The two stars are separated about 4 arcseconds away, and because of their slow orbital motion the orbit is poorly known: estimates of the orbital period range from 970 years to over 1,500 years. There is a th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sigma1 Ursae Majoris
Sigma1 Ursae Majoris (σ1 UMa) is the Bayer designation for a solitary star in the northern circumpolar constellation of Ursa Major. With an apparent visual magnitude of 5.14 it is faintly visible to the naked eye on dark nights. Based upon an annual parallax shift of 6.26 mas, it is located roughly 520 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction factor of 0.06 due to interstellar dust. This is an evolved K-type giant star with a stellar classification of K5 III. It is a suspected variable with an amplitude of 0.03 magnitude. The measured angular diameter of the star after correcting for limb darkening is , which, at the estimated distance of this star, yields a physical size of about 46 times the radius of the Sun. The star is radiating around 560 times the solar luminosity from its outer atmosphere at an effective temperature The effective temperature of a body such as a star or pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
4 Ursae Majoris
4 Ursae Majoris (sometimes abbreviated 4 Uma) is the Flamsteed designation of a star in the northern circumpolar constellation of Ursa Major. It also bears the Bayer designation of Pi2 Ursae Majoris (Pi2 UMa, π2 Ursae Majoris, π2 UMa) and is traditionally named Muscida. With an apparent visual magnitude of +4.6, this star is visible from suburban or darker skies based upon the Bortle Dark-Sky Scale. From parallax measurements made during the ''Hipparcos'' mission, this star is at a distance of from Earth. , one extrasolar planet has been confirmed to be orbiting the star. Properties This star has a stellar classification of K2 III, indicating that, at an estimated age of around four billion years, it is an evolved star that has reached the giant stage. It has a mass about 1.2 times larger than the Sun, but has expanded to 18 times the Sun's girth. The effective temperature of the star's outer atmosphere is . This heat gives it the cool, orange-h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pi1 Ursae Majoris
Pi1 Ursae Majoris (Pi1 UMa, π¹ Ursae Majoris, π¹ UMa) is a yellow G-type main sequence dwarf with a mean apparent magnitude of +5.63. It is approximately 46.8 light years from Earth, and is a relatively young star with an age of about 200 million years. It is classified as a BY Draconis type variable star and its brightness varies by 0.08 magnitudes. In 1986, it became the first solar-type star to have the emission from an X-ray flare observed. Based upon its space velocity components, this star is a member of the Ursa Major moving group of stars that share a common motion through space. An excess of infrared radiation has been detected from this system, which suggests the presence of a debris disk A debris disk (American English), or debris disc (Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris dis . ... [...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, including 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 straightf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosphere
The photosphere is a star's outer shell from which light is radiated. The term itself 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. 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 deepest region of a luminous object, usually a star, that is transparent to photons of certain wavelengths. Temperature The surface of a star is defined to have a temperature given by the effective temperature in the Stefan–Boltzmann law. 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. Composition of the Sun The Sun is composed primarily of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sun's Luminosity
The solar luminosity (), is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, 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 does not include the solar neutrino luminosity, which would add , or , i.e. a total of (the mean energy of the solar photons is 26 MeV and that of the solar neutrinos 0.59 MeV, i.e. 2.27%; the Sun emits photons and as many neutrinos each second, of which per m2 reach the Earth each second). The Sun is a weakly variable star, and its actual luminosity therefore 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 solar irradiance (the sola ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rotation Period
The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the background stars, measured in sidereal time. The other type of commonly used rotation period is the object's synodic rotation period (or ''solar day''), measured in solar time, which may differ by a fraction of a rotation or more than one rotation to accommodate the portion of the object's orbital period during one day. Measuring rotation For solid objects, such as rocky planets and asteroids, the rotation period is a single value. For gaseous or fluid bodies, such as stars and gas giants, the period of rotation varies from the object's equator to its pole due to a phenomenon called differential rotation. Typically, the stated rotation period for a gas giant (such as Jupiter, Saturn, Uranus, Neptune) is its internal rotation period, as d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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