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IC 1396
IC 1396 is a large emission nebulae, a region of ionized gas, located in the constellation Cepheus about 2,400 light years away from Earth. IC 1396 is illuminated and ionized by a very bright, massive multiple star HD 206267 at its center, except for dense globules that can protect themselves from the star's harsh ultraviolet rays. This hierarchical triple star system has two members that form a spectroscopic binary that orbit each other with a period of 3.7 days, while a third member lies further away—it is unclear whether this third member is gravitationally bound to the pair. The system is emitting a stellar wind that reaches an exceptional velocity of 3,225 km/s, among the highest measured for stars of this type. Jutting from the rim of the nebula is IC 1396A, commonly called the Elephant's Trunk Nebula, a dark, dense globule with a bright, sinuous rim being illuminated by HD 206267. See also * List of largest nebulae * Lists of nebulae References Sources * * ... [...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] |
Cepheus (constellation)
Cepheus is a constellation in the deep northern sky, named after Cepheus, King of Aethiopia, Cepheus, a king of Aethiopia in Greek mythology. It is one of the 48 constellations listed by the second century astronomer Ptolemy, and it remains one of the 88 constellations in the modern times. The constellation's brightest star is Alderamin (Alpha Cephei), with an apparent magnitude of 2.5. Delta Cephei is the prototype of an important class of star known as a Cepheid variable. RW Cephei, an orange hypergiant, together with the red supergiants Mu Cephei, MY Cephei, VV Cephei, V381 Cephei, and V354 Cephei are among the List of largest stars, largest stars known. In addition, Cepheus also has the hyperluminous quasar S5 0014+81, which hosts an ultramassive black hole in its core, reported at 40 billion solar masses, about 10,000 times more massive than the Sagittarius A*, central black hole of the Milky Way, making this among the most List of most massive black holes, massive black ho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Emission Nebulae
An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Among the several different types of emission nebulae are H II regions, in which star formation is taking place and young, massive stars are the source of the ionizing photons; and planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them.Nebulae [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light Year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astronomical Union (IAU), a light-year is the distance that Speed of light, light travels in vacuum in one Julian year (astronomy), Julian year (365.25 days). Despite its inclusion of the word "year", the term should not be misinterpreted as a unit of time. The ''light-year'' is most often used when expressing distances to stars and other distances on a Galaxy, galactic scale, especially in public understanding of science, non-specialist contexts and popular science publications. The unit most commonly used in professional astronomy is the parsec (symbol: pc, about 3.26 light-years). Definitions As defined by the International Astronomical Union (IAU), the light-year is the product of the Julian year (astronomy), Julian ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HD 206267
HD 206267A is a hierarchical triple star system in the northern circumpolar constellation of Cepheus. Two of the members form a spectroscopic binary that orbit each other with a period of 3.7 days, while a third member lies further away—it is unclear whether this third member is gravitationally bound to the pair. The system is emitting a stellar wind that reaches an exceptional velocity of 3,225 km/s, among the highest measured for stars of this type. This stellar system lies in the nebula IC 1396. All three components are massive stars, and the intense ultraviolet radiation they give off ionizes the gas of IC 1396, and causes compression denser globules of the nebula, leading to star formation. The stellar wind produced by the stars is strong enough to strip nearby stars of their protoplanetary disks. The system is a member of the Cepheus OB2 stellar association A stellar association is a very loose star cluster, looser than both open clusters and globular ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triple Star
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking, they are also star systems. Star systems are not to be confused with planetary systems, which include planets and similar bodies (such as comets). Terminology A star system of two stars is known as a ''binary star'', ''binary star system'' or ''physical double star''. Systems with four or more components are rare, and are much less commonly found than those with 2 or 3. Multiple-star systems are called ''triple'', ''ternary'', or ''trinary'' if they contain three stars; ''quadruple'' or ''quaternary'' if they contain four stars; ''quintuple'' or ''quintenary'' with five stars; ''sextuple'' or ''sextenary'' with six stars; ''septuple'' or ''septenary'' with seven stars; and ''octuple' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectroscopic Binary
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. I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravitationally Bound
The gravitational binding energy of a system is the minimum energy which must be added to it in order for the system to cease being in a gravitationally bound state. A gravitationally bound system has a lower (''i.e.'', more negative) gravitational potential energy than the sum of the energies of its parts when these are completely separated—this is what keeps the system aggregated in accordance with the minimum total potential energy principle. The gravitational binding energy can be conceptually different within the theories of Newtonian gravity and Albert Einstein's theory of gravity called General Relativity. In Newtonian gravity, the binding energy can be considered to be the linear sum of the interactions between all pairs of microscopic components of the system, while in General Relativity, this is only approximately true if the gravitational fields are all weak. When stronger fields are present within a system, the binding energy is a nonlinear property of the sys ... [...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] |
List Of Largest Nebulae
Below is a list of the largest known nebulae so far discovered, ordered by actual diameter. This list is prone to change because of inconsistencies between studies, the great distances of nebulae from our stellar neighborhood, and the constant refinement of technology and engineering. Caveats Nebulae have no standardized boundaries, so the measurements are subject to revision. Furthermore, scientists are still defining the features and parameters of nebulae. Because of these rapid developments and adjustments, this list may be unreliable. Lyman alpha nebulae around quasars can have sizes between 15 kpc and 460 kpc. Especially large Enormous Lyα nebula (ELAN) can have large sizes of ≳100 kpc. Farina et al. 2019 table 5 has an extensive compilation of Lyman alpha nebulae around quasars. For now this list contains only the largest ELANs, with sizes larger than 300 kpc. List See also * List of largest cosmic structures *List of largest known stars * List of largest plane ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lists Of Nebulae
The following articles contain lists of nebulae: *List of dark nebulae * List of diffuse nebulae * List of largest nebulae * List of planetary nebulae * List of protoplanetary nebulae * List of supernova remnants See also * Lists of astronomical objects This is a list of lists, grouped by type of astronomical object. Solar System * List of Solar System objects * List of gravitationally rounded objects of the Solar System * List of Solar System objects most distant from the Sun * List of ... {{DEFAULTSORT:Nebulae ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
