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WR 147
WR 147 is a multiple star system in the constellation of Cygnus. The system is extremely reddened by interstellar extinction – that is, dust in front of the star scatters much of the blue light coming from WR 147, leaving the star appearing reddish. Distance The distance of WR 147 has been calculated to be based on infrared photometry, which would place it in front of the OB association known as Cygnus OB2. The extinction in the visual range was calculated to be 11.5 magnitudes and the absolute visual magnitude assumed to be −6.7. This would make WR 147 one of the closest known Wolf-Rayet stars, despite its faint apparent magnitude. A later calculation using optical and ultraviolet photometry derived a slightly lower value for the extinction. Combined with an assumption of a brighter absolute magnitude, this gave a distance modulus of 10.6 corresponding to a distance of about 1,200 pc. This is still one of the nearest Wolf–Rayet systems to the sun. A Gaia Data Rel ... [...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] |
B-type Star
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] |
Plasma (physics)
Plasma () is a state of matter characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, mostly in stars (including the Sun), but also dominating the rarefied intracluster medium and Outer space#Intergalactic space, intergalactic medium. Plasma can be artificially generated, for example, by heating a neutral gas or subjecting it to a strong electromagnetic field. The presence of charged particles makes plasma electrically conductive, with the dynamics of individual particles and macroscopic plasma motion governed by collective electromagnetic fields and very sensitive to externally applied fields. The response of plasma to electromagnetic fields is used in many modern devices and technologies, such as plasma display, plasma televisions or plasma etching. Depending on temperature and density, a certain number of neutral particles may also be present, in wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radio Wave
Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths greater than , about the diameter of a grain of rice. Radio waves with frequencies above about 1 GHz and wavelengths shorter than 30 centimeters are called microwaves. Like all electromagnetic waves, radio waves in vacuum travel at the speed of light, and in the Earth's atmosphere at a slightly lower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical radio source, astronomical objects, and are part of the blackbody radiation emitted by all warm objects. Radio waves are generated artificially by an electronic device called a transmitter, which is connected to an antenna (radio), antenna, w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ranging from 10 Nanometre, nanometers to 10 Picometre, picometers, corresponding to frequency, frequencies in the range of 30 Hertz, petahertz to 30 Hertz, exahertz ( to ) and photon energies in the range of 100 electronvolt, eV to 100 keV, respectively. X-rays were discovered in 1895 in science, 1895 by the German scientist Wilhelm Röntgen, Wilhelm Conrad Röntgen, who named it ''X-radiation'' to signify an unknown type of radiation.Novelline, Robert (1997). ''Squire's Fundamentals of Radiology''. Harvard University Press. 5th edition. . X-rays can penetrate many solid substances such as construction materials and living tissue, so X-ray radiography is widely used in medical diagnostics (e.g., checking for Bo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stellar Wind
A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. Different stellar classification, types of stars have different types of stellar winds. Post-main sequence, main-sequence stars nearing the ends of their lives often eject large quantities of mass in massive ( \scriptstyle \dot > 10^ solar masses per year), slow (v = 10 km/s) winds. These include red giants and Red supergiant, supergiants, and asymptotic giant branch stars. These winds are understood to be driven by radiation pressure on Cosmic dust, dust condensing in the upper atmosphere of the stars. Young T Tauri stars often have very powerful stellar winds. Massive stars of stellar classification, types O star, O and B V star, B have stellar winds with lower mass loss rates (\scriptstyle \dot 1–2000 km ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orbital Motion
In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a planet, moon, asteroid, or Lagrange point. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the center of mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion. For most situations, orbital motion is adequately approximated by Newtonian mechanics, which explains gravity as a force obeying an inverse-square law. However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature of spacetime, with orbits following geodesics, provides a more accurate calculation and understa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orbit
In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a planet, moon, asteroid, or Lagrange point. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the center of mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion. For most situations, orbital motion is adequately approximated by Newtonian mechanics, which explains gravity as a force obeying an inverse-square law. However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature of spacetime, with orbits following geodesics, provides a more accurate calculation and u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orbital Element
Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same orbit, but certain schemes are commonly used in astronomy and orbital mechanics. A real orbit and its elements change over time due to gravitational perturbations by other objects and the effects of general relativity. A Kepler orbit is an idealized, mathematical approximation of the orbit at a particular time. When viewed from an inertial frame, two orbiting bodies trace out distinct trajectories. Each of these trajectories has its focus at the common center of mass. When viewed from a non-inertial frame centered on one of the bodies, only the trajectory of the opposite body is apparent; Keplerian elements describe these non-inertial trajectories. An orbit has two sets of Keplerian elements depending on which body is used as the point ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Most Luminous Stars
This is a list of stars arranged by their absolute magnitude – their intrinsic stellar luminosity. This cannot be observed directly, so instead must be calculated from the apparent magnitude (the brightness as seen from Earth), the distance to each star, and a correction for interstellar extinction. The entries in the list below are further corrected to provide the bolometric magnitude, i.e. integrated over all wavelengths; this relies upon measurements in multiple photometric filters and extrapolation of the stellar spectrum based on the stellar spectral type and/or effective temperature. Entries give the bolometric luminosity in multiples of the luminosity of the Sun () and the bolometric absolute magnitude. As with all magnitude systems in astronomy, the latter scale is logarithmic and inverted i.e. more negative numbers are more luminous. Most stars on this list are not bright enough to be visible to the naked eye from Earth, because of their high distances, hig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neptune
Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth. Compared to Uranus, its neighbouring ice giant, Neptune is slightly smaller, but more massive and denser. Being composed primarily of gases and liquids, it has no well-defined solid surface. Neptune orbits the Sun once every 164.8 julian year (astronomy), years at an orbital distance of . It is named after Neptune (mythology), the Roman god of the sea and has the astronomical symbol representing Trident of Poseidon, Neptune's trident. Neptune is not visible to the unaided eye and is the only planet in the Solar System that was not initially observed by direct empirical observation. Rather, unexpected changes in the orbit of Uranus led Alexis Bouvard to hypothesise that its orbit was subject to gravitational Pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Angular Separation
Angular distance or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When the rays are lines of sight from an observer to two points in space, it is known as the apparent distance or apparent separation. Angular distance appears in mathematics (in particular geometry and trigonometry) and all natural sciences (e.g., kinematics, astronomy, and geophysics). In the classical mechanics of rotating objects, it appears alongside angular velocity, angular acceleration, angular momentum, moment of inertia and torque. Use The term ''angular distance'' (or ''separation'') is technically synonymous with ''angle'' itself, but is meant to suggest the linear distance between objects (for instance, a pair of stars observed from Earth). Measurement Since the angular distance (or separation) is conceptually identical to an ang ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
