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Bow Shock
In astrophysics, bow shocks are shock waves in regions where the conditions of density and pressure change dramatically due to blowing stellar wind. Bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby flowing ambient plasma such as the solar wind. For Earth and other magnetized planets, it is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause. For stars, this boundary is typically the edge of the astrosphere, where the stellar wind meets the interstellar medium. Description The defining criterion of a shock wave is that the bulk velocity of the plasma drops from " supersonic" to "subsonic", where the speed of sound cs is defined by c_s^2 = \gamma p/ \rho where \gamma is the ratio of specific heats, p is the pressure, and \rho is the density of the plasma. A common complication in astrophysics is the presence of a magnetic field. For instance, the charged particl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
52706main Hstorion Lg
5 (five) is a number, numeral and digit. It is the natural number, and cardinal number, following 4 and preceding 6, and is a prime number. Humans, and many other animals, have 5 digits on their limbs. Mathematics 5 is a Fermat prime, a Mersenne prime exponent, as well as a Fibonacci number. 5 is the first congruent number, as well as the length of the hypotenuse of the smallest integer-sided right triangle, making part of the smallest Pythagorean triple ( 3, 4, 5). 5 is the first safe prime and the first good prime. 11 forms the first pair of sexy primes with 5. 5 is the second Fermat prime, of a total of five known Fermat primes. 5 is also the first of three known Wilson primes (5, 13, 563). Geometry A shape with five sides is called a pentagon. The pentagon is the first regular polygon that does not tile the plane with copies of itself. It is the largest face any of the five regular three-dimensional regular Platonic solid can have. A conic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Venus
Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker and denser than Earth and any other rocky body in the Solar System. Its atmosphere is composed of mostly carbon dioxide (), with a global sulfuric acid cloud cover and no liquid water. At the mean surface level the atmosphere reaches a temperature of and a pressure 92 times greater than Earth's at sea level, turning the lowest layer of the atmosphere into a supercritical fluid. Venus is the third brightest object in Earth's sky, after the Moon and the Sun, and, like Mercury, appears always relatively close to the Sun, either as a "morning star" or an "evening star", resulting from orbiting closer ( inferior) to the Sun than Earth. The orbits of Venus and Earth make the two planets approach each other in synodic periods of 1.6 years ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar System" and "solar system" structures in theinaming guidelines document. The name is commonly rendered in lower case ('solar system'), as, for example, in the ''Oxford English Dictionary'' an''Merriam-Webster's 11th Collegiate Dictionary''. is the gravitationally bound Planetary system, system of the Sun and the objects that orbit it. It Formation and evolution of the Solar System, formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is a typical star that maintains a hydrostatic equilibrium, balanced equilibrium by the thermonuclear fusion, fusion of hydrogen into helium at its stellar core, core, releasing this energy from its outer photosphere. As ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
67P/Churyumov–Gerasimenko
67P/Churyumov–Gerasimenko (abbreviated as 67P or 67P/C–G) is a Jupiter-family comet. It is originally from the Kuiper belt and has an orbital period of 6.45 years as of 2012, a rotation period of approximately 12.4 hours, and a maximum velocity of . Churyumov–Gerasimenko is approximately at its longest and widest dimensions. It was first observed on photographic plates in 1969 by Soviet astronomers Klim Churyumov, Klim Ivanovych Churyumov and Svetlana Gerasimenko, Svetlana Ivanovna Gerasimenko, after whom it is Naming of comets, named. It most recently came to Perihelion and aphelion, perihelion (closest approach to the Sun) on 2 November 2021, and will next come to perihelion on 9 April 2028. Churyumov–Gerasimenko was the destination of the European Space Agency's Rosetta (spacecraft), ''Rosetta'' mission, launched on 2 March 2004. ''Rosetta'' space rendezvous, rendezvoused with Churyumov–Gerasimenko on 6 August 2014 and entered orbit on 10 September 2014. ''Rosetta' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rosetta (spacecraft)
''Rosetta'' was a space probe built by the European Space Agency that launched on 2 March 2004. Along with ''Philae'', its lander module, ''Rosetta'' performed a detailed study of comet 67P/Churyumov–Gerasimenko (67P). During its journey to the comet, the spacecraft performed flybys of Earth, Mars, and the asteroids 21 Lutetia and 2867 Šteins. It was launched as the third cornerstone mission of the ESA's Horizon 2000 programme, after ''SOHO' Cluster'' and '' XMM-Newton''. On 6 August 2014, the spacecraft reached the comet and performed a series of manoeuvers to eventually orbit the comet at distances of . On 12 November, its lander module ''Philae'' performed the first successful landing on a comet, though its battery power ran out two days later. Communications with ''Philae'' were briefly restored in June and July 2015, but due to diminishing solar power, ''Rosetta'' communications module with the lander was turned off on 27 July 2016. On 30 September 2016, the ''Rosett ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perihelion And Aphelion
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides pertaining to orbits around different bodies have distinct names to differentiate themselves from other apsides. Apsides pertaining to geocentric orbits, orbits around the Earth, are at the farthest point called the ''apogee'', and at the nearest point the ''perigee'', like with orbits of satellites and the Moon around Earth. Apsides pertaining to orbits around the Sun are named ''aphelion'' for the farthest and ''perihelion'' for the nearest point in a heliocentric orbit. Earth's two apsides are the farthest point, ''aphelion'', and the nearest point, ''perihelion'', of its orbit around the host Sun. The terms ''aphelion'' and ''perihelion'' apply in the same way to the orbits of Jupiter and the other planets, the comets, and the asteroids of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
26P/Grigg–Skjellerup
Comet Grigg–Skjellerup (formally designated 26P/Grigg–Skjellerup) is a periodic comet. It was visited by the ''Giotto'' probe in July 1992. The spacecraft came as close as 200 km, but could not take pictures because some instruments were damaged from its encounter with Halley's Comet. The comet last came to perihelion (closest approach to the Sun) on 25 December 2023, but was 1.8 AU from Earth and only 31 degrees from the Sun. History of observation The comet was discovered in 1902 by John Grigg of New Zealand, and rediscovered in its next appearance in 1922 by John Francis Skjellerup, an Australian then living and working for about two decades in South Africa where he was a founder member of the Astronomical Society of Southern Africa. In 1987, it was belatedly discovered by Ľubor Kresák that the comet had been observed in 1808 as well, by Jean-Louis Pons. Pons observed the comet on 6 and 9 February, which was insufficient to calculate an approximate orbit. In 197 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halley's Comet
Halley's Comet is the only known List of periodic comets, short-period comet that is consistently visible to the naked eye from Earth, appearing every 72–80 years, though with the majority of recorded apparitions (25 of 30) occurring after 75–77 years. It last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061. Officially designated 1P/Halley, it is also commonly called Comet Halley, or sometimes simply Halley. Halley's periodic returns to the inner Solar System have been observed and recorded by astronomers around the world since at least 240 BC, but it was not until 1705 that the English astronomer Edmond Halley understood that these appearances were re-appearances of the same comet. As a result of this discovery, the comet is named after Halley. During its 1986 visit to the inner Solar System, Halley's Comet became the first comet to be observed in detail by a spacecraft, ''Giotto (spacecraft), Giotto'', providing the first obser ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
21P/Giacobini–Zinner
Comet Giacobini–Zinner (officially designated as 21P/Giacobini–Zinner) is a periodic comet in the Solar System. It was discovered by Michel Giacobini, who observed it in the constellation of Aquarius on 20 December 1900. It was recovered two orbits later by Ernst Zinner, while he was observing variable stars near Beta Scuti on 23 October 1913. Physical properties The comet nucleus is estimated to be in diameter. During its apparitions, Giacobini–Zinner can reach about the 7-8th magnitude, but in 1946 it underwent a series of outbursts that made it as bright as 5th magnitude. It is the parent body of the Giacobinids meteor shower (also known as the Draconids). The comet currently has a minimum orbit intersection distance to Earth of . During the apparition of 2018, the optical spectra have revealed the comet is depleted in carbon-chain molecules and carbon dioxide, likely indicating its origin in relatively warm portion of the Solar system. Exploration Giacobi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coma (cometary)
The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes near the Sun in its highly elliptical orbit. As the comet warms, parts of it sublimate; this gives a comet a diffuse appearance when viewed through telescopes and distinguishes it from stars. The word ''coma'' comes from the Greek (), which means "hair" and is the origin of the word ''comet'' itself. The coma is generally made of ice and comet dust. Water composes up to 90% of the volatiles that outflow from the nucleus when the comet is within from the Sun. The H2O parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization. The solar wind plays a minor role in the destruction of water compared to photochemistry. Larger dust particles are left along the comet's orbital path while smaller particles are pushed away from the Sun into the comet's tail by light pressure. On 11 August 2014, astronomers released studies, using the A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cometary Nucleus
The nucleus is the solid, central part of a comet, formerly termed a ''dirty snowball'' or an ''icy dirtball''. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublime and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. A typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust. Results from the ''Rosetta'' and ''Philae'' spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals. Further, the ALICE spectrograph on ''Rosetta'' determined that electrons (within above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comet
A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding the nucleus, and sometimes a Comet tail, tail of gas and dust gas blown out from the coma. These phenomena are due to the effects of solar radiation and the outstreaming solar wind plasma acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently close and bright, a comet may be seen from Earth without the aid of a telescope and can Subtended angle, subtend an arc of up to 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
