proper motion

At present, binary stars are classified into four types according to their observable properties: visual binaries spectroscopic binaries eclipsing binaries astrometric binaries Any star can belong to several of these classes, e.g., several spectroscopic binaries are also eclipsing binaries. Another three-category classification is based on the distance of the stars, relative to their sizes : detached binaries ...

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Binary star, Binary star - Binary star classifications, Binary star - Research findings, Binary star - Binary star examples, Binary star - Binary stars in fiction

Read more here: » Binary star: Encyclopedia II - Binary star - Binary star classifications

Normally when the Earth and Venus are in conjunction they are not aligned with the Sun. Venus' orbit is inclined by 3.4° to the Earth's so it appears to pass under (or over) the Sun in the sky. Transits occur when the two planets happen to be in conjunction at (or very near) the points where their orbital planes cross. Although 3.4° may not seem like much, Venus can be as far as 9.6° from the Sun when viewed from the Earth at inferior conjunction. Since the angular diameter of the Sun is about half a degree, Venus may appear to pass above or below ...

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Transit of Venus, Transit of Venus - Conjunctions of Venus with the Sun, Transit of Venus - Scientific interest in transits, Transit of Venus - Past and future transits, Transit of Venus - Observing transits of Venus, Transit of Venus - Grazing transits of Venus, Transit of Venus - Simultaneous transits, Transit of Venus - Cultural meaning

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Sometimes Venus only grazes the Sun during a transit. In this case it is possible that in some areas of the Earth a full transit can be seen while in other regions there is only a partial transit (no second or fourth contact). The last transit of this type was on December 6th, 1631, while the next such transit will occur on December 13th, 2611. It is also possible that a transit of Venus can be seen in some parts of the world as a partial transit, while in others Venus misses the Sun. Such a transit last occurred on November 19th, 541BC, and th ...

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Transit of Venus, Transit of Venus - Conjunctions of Venus with the Sun, Transit of Venus - Scientific interest in transits, Transit of Venus - Past and future transits, Transit of Venus - Observing transits of Venus, Transit of Venus - Grazing transits of Venus, Transit of Venus - Simultaneous transits, Transit of Venus - Cultural meaning

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In many cultures of the world, the transit of Venus across the Sun has been regarded as a rare and therefore an important event that marks major changes in human history. This is true for the Maya and other ancient American civilizations, for the Indian Vedic traditions and for the Western astrology of Mesopotamian origin. It has been claimed that a transit led to the ancient Greeks celebrating the Ancient Olympics every four years as a form of commemoration. The efforts of Guillaume Le Gentil to observe the transit of Venus in different parts of the globe, became the subject of the fictiona ...

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Transit of Venus, Transit of Venus - Conjunctions of Venus with the Sun, Transit of Venus - Scientific interest in transits, Transit of Venus - Past and future transits, Transit of Venus - Observing transits of Venus, Transit of Venus - Grazing transits of Venus, Transit of Venus - Simultaneous transits, Transit of Venus - Cultural meaning

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The simultaneous occurrence of a transit of Mercury and a transit of Venus is possible, but only in the distant future. Such an event will next occur only in the years 69163 and 224508. The simultaneous occurrence of a solar eclipse and a transit of Venus is currently possible, but very rare. The next solar eclipse occurring during a transit of Venus will be on April 5 15232. Only 5 hours after the transit of Venus on June 4, 1769 there was a total solar eclipse, which was visible in Northern America, Europe and Northern Asia almost as partial solar eclipse. This was the lowest time difference between a trans ...

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Transit of Venus, Transit of Venus - Conjunctions of Venus with the Sun, Transit of Venus - Scientific interest in transits, Transit of Venus - Past and future transits, Transit of Venus - Observing transits of Venus, Transit of Venus - Grazing transits of Venus, Transit of Venus - Simultaneous transits, Transit of Venus - Cultural meaning

Read more here: » Transit of Venus: Encyclopedia II - Transit of Venus - Simultaneous transits

Spectroscopic observations of HH objects show that they are moving away from the source stars at speeds of 100 to 1000 km/s. In recent years, the high optical resolution of Hubble Space Telescope observations has revealed the proper motion of many HH objects in observations spaced several years apart. These observations have also allowed estimates of the distances of some HH objects via the expansion parallax method. As they move away from the parent star, HH objects evolve significantly, varying in brightness on timescales of a ...

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Herbig-Haro object, Herbig-Haro object - Discovery and history of observations, Herbig-Haro object - Physical characteristics, Herbig-Haro object - Numbers and distribution, Herbig-Haro object - Proper motions and variability, Herbig-Haro object - Source stars

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Over 400 individual HH objects or groups are now known. They are ubiquitous in star-forming H II regions, and are often found in large groups. They are typically observed near Bok globules (dark nebulae which contain very young stars) and often emanate from them. Frequently, several HH objects are seen near a single energy source, forming a string of objects along the line of the polar axis of the parent star. The number of known HH objects has increased rapidly over the last few years, but is still thought to be a very small proporti ...

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Herbig-Haro object, Herbig-Haro object - Discovery and history of observations, Herbig-Haro object - Physical characteristics, Herbig-Haro object - Numbers and distribution, Herbig-Haro object - Proper motions and variability, Herbig-Haro object - Source stars

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At present, binary stars are classified into four types according to their observable properties: visual binaries spectroscopic binaries eclipsing binaries astrometric binaries Any star can belong to several of these classes, e.g., several spectroscopic binaries are also eclipsing binaries. Another three-category classification is based on the distance of the stars, relative to their sizes : detached binaries ...

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Binary star, Binary star - Background, Binary star - Binary star classifications, Binary star - Research findings, Binary star - Binary star examples, Binary star - Binary stars in fiction

Read more here: » Binary star: Encyclopedia II - Binary star - Binary star classifications

Computer models of planetary formation suggest that terrestrial planets would be able to form close to both Alpha Centauri A and B, but that gas giant planets similar to our Jupiter and Saturn would not be able to form because of the binary stars' gravitational effects. Given the similarities in star type, age and stability of the orbits it has been suggested that this solar system may hold one of the best possibilities for extraterrestrial life. However, some astronomers have speculated that any terrestrial planets in the Alpha Centauri sys ...

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Alpha Centauri, Alpha Centauri - Names, Alpha Centauri - System components, Alpha Centauri - Possibility of planet formation, Alpha Centauri - Sky appearance from Alpha Centauri, Alpha Centauri - Apparent movement, Alpha Centauri - Alpha Centauri in fiction

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During the past 200 years a large amount of research has been carried out on binary stars leading to some general conclusions. It is believed that at least a quarter of all stars are at least binary systems, with as many as 10% of these systems containing more than two stars (ternary etc.). There is a direct correlation between the period of revolution of a binary star and the eccentricity of its orbit, with systems of short period having smaller eccentricity. Binary stars may be found with any conceivable separation, from pair ...

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Binary star, Binary star - Background, Binary star - Binary star classifications, Binary star - Research findings, Binary star - Binary star examples, Binary star - Binary stars in fiction

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The constellation bears a resemblance to a wide winged, long necked bird, in graceful flight [1]. In Greek mythology, the constellation represents several different legendary swans. Zeus disguised himself as a swan to rape Leda, who gave birth to the Gemini, Helen of Troy, and Clytemnestra. Orpheus was transformed into a swan after his murder, and was said to have been placed in the sky next to his lyre (Lyra). Finally, it is said that a youth named Cygnus was the boyfriend of the ill-fated Phaethon. After Phaethon was killed t ...

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Cygnus constellation, Cygnus constellation - Notable features, Cygnus constellation - Notable deep sky objects, Cygnus constellation - History and mythology, Cygnus constellation - Stars, Cygnus constellation - In Art and Literature

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Emission from HH objects is caused by shock waves when they collide with the interstellar medium, but their motions are complicated. Spectroscopic observations of their doppler shifts indicate velocities of several hundred kilometres per second, but the emission lines in the spectra of HH objects are too weak to have been formed in such high speed collisions. This probably means that some of the material they are colliding with is also moving outwards, although at a slower speed ^{See also:}

Herbig-Haro object, Herbig-Haro object - Discovery and history of observations, Herbig-Haro object - Physical characteristics, Herbig-Haro object - Numbers and distribution, Herbig-Haro object - Proper motions and variability, Herbig-Haro object - Source stars

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Alpha Centauri is a triple star system. It consists of two main stars, Alpha Centauri A and Alpha Centauri B (which form a binary star together) at a distance of 4.36 ly, and a dimmer red dwarf named Proxima Centauri at a distance of 4.22 ly. Both of the two main stars are rather similar to the Sun. The larger member of the binary star, Alpha Centauri A, is the most similar to the Sun, but a little larger and brighter. Like the Sun, its spectral type is G2 V, and, like the sun, shines in a yellowish-white light. The smal ...

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Alpha Centauri, Alpha Centauri - Names, Alpha Centauri - System components, Alpha Centauri - Possibility of planet formation, Alpha Centauri - Sky appearance from Alpha Centauri, Alpha Centauri - Apparent movement, Alpha Centauri - Alpha Centauri in fiction

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There are over 1,000 known open clusters in our galaxy, but the true total may be up to ten times higher than that [8]. In spiral galaxies, open clusters are invariably found in the spiral arms where gas densities are highest and so most star formation occurs, and clusters usually disperse before they have had time to travel beyond their spiral arm. Open clusters are strongly concentrated close to the galactic plane, with a scale height in our galaxy o ...

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Open cluster, Open cluster - Historical observations, Open cluster - Formation, Open cluster - Morphology and classification, Open cluster - Numbers and distribution, Open cluster - Stellar composition, Open cluster - Eventual fate, Open cluster - Studying stellar evolution, Open cluster - Open clusters and the astronomical distance scale

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The constellation bears a resemblence to a wide winged, long necked bird, in graceful flight [1]. In Greek mythology, the constellation represents several different legendary swans. Zeus disguised himself as a swan to rape Leda, who gave birth to the Gemini, Helen of Troy, and Clytemnestra. Orpheus was transformed into a swan after his murder, and was said to have been placed in the sky next to his lyre (Lyra). Finally, it is said that a youth named Cygnus was the boyfriend of the ill-fated Phaethon. After Phaethon was killed t ...

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Cygnus constellation, Cygnus constellation - Notable features, Cygnus constellation - Notable deep sky objects, Cygnus constellation - History and mythology, Cygnus constellation - Stars, Cygnus constellation - In Art and Literature

Read more here: » Cygnus constellation: Encyclopedia II - Cygnus constellation - History and mythology

Because of its status as our star's nearest galactic neighbor, Alpha Centauri has frequently been referred to in science fiction stories involving interstellar travel. In The Centauri Device (1975) by M. John Harrison the native Centaurians (humanoid aliens able to interbreed with humans) have been wiped out in a genocidal attack by expanding Earth colonisation of the galaxy. The novel's main character, whose mother was Centauran, is one of the few people in the cosmos able to operate t ...

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Alpha Centauri, Alpha Centauri - Names, Alpha Centauri - System components, Alpha Centauri - Possibility of planet formation, Alpha Centauri - Sky appearance from Alpha Centauri, Alpha Centauri - Apparent movement, Alpha Centauri - Alpha Centauri in fiction

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Aries' stars are rather faint except for α Ari (Hamal) and β Ari (Sharatan). Other important stars are γ Ari (Mesarthim) and δ Ari (Botein). Teegarden's star, in Aries, is one of our sun's closest neighbours. ...

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Aries, Aries - Notable features, Aries - Notable deep sky objects, Aries - Mythology, Aries - Astrology, Aries - Notable and named stars

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The world's first star catalogue was made by Gan De, a Chinese astronomer in 4th century BC. Although no longer in serious use, mention should be made of Ptolemy's star catalogue published in the 2nd century as part of his Almagest, which lists 1,022 stars visible from Alexandria. It was the standard star catalogue in the Western and Arab worlds for over a thousand years. Ptolemy's catalogue was based almost entirely on an earlier one by Hipparchus from the 2nd century B.C. (Newton 1977; Rawlins 1982). An even earlier star catalogue was that of Timocharis of Alexandria, which ...

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Star catalogue, Star catalogue - Historical catalogues, Star catalogue - Full-sky catalogues, Star catalogue - HD/HDE, Star catalogue - SAO, Star catalogue - BD/CD/CPD, Star catalogue - AC, Star catalogue - USNO-B1.0, Star catalogue - Specialized catalogues, Star catalogue - ADS, Star catalogue - BS BSC HR, Star catalogue - GJ Gliese Gl, Star catalogue - GCTP, Star catalogue - HIP, Star catalogue - Proper motion catalogues

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Discoveries regarding extrasolar planets were first published in 1989, [1] [2] when variations in the radial velocities of HD 114762 and Alrai (γ Cephei) were explained as being caused by sub-brown dwarf masses, possibly giant planets (11 MJ & 2-3 MJ respectively). Alrai had been the subject of a paper [3] the year before, but the question of a planetary companion as the cause was left open. Subsequent work in 1992 however concluded that the data were not solid enough to declare the presence of a planet, [4] althou ...

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Extrasolar planet, Extrasolar planet - History of detection, Extrasolar planet - Methods of detection, Extrasolar planet - Pulsar timing, Extrasolar planet - Astrometry, Extrasolar planet - Radial velocity, Extrasolar planet - Gravitational microlensing, Extrasolar planet - Transit method, Extrasolar planet - Circumstellar disks, Extrasolar planet - Direct observation, Extrasolar planet - Solar system formation processes, Extrasolar planet - Notable extrasolar planets, Extrasolar planet - Table of extremes

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Alpha Centauri is a triple star system. It consists of two main stars, Alpha Centauri A and Alpha Centauri B (which form a binary star together) at a distance of 4.36 ly, and a dimmer red dwarf named Proxima Centauri at a distance of 4.22 ly. The larger member of the binary star, Alpha Centauri A, is similar to the Sun, but a little larger and brighter. Like the Sun, its spectral type is G2 V. The smaller of the two, Alpha Centauri B, is dimmer, with a spectral type of K1 V. The two orbit one another elliptically ...

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Alpha Centauri, Alpha Centauri - Names, Alpha Centauri - System components, Alpha Centauri - Possibility of planet formation, Alpha Centauri - Sky appearance from Alpha Centauri, Alpha Centauri - Apparent movement, Alpha Centauri - Alpha Centauri in fiction

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It bears the proper name Rigil Kentaurus (often shortened to Rigil Kent), derived from the Arabic phrase Al Rijl al Kentaurus, meaning "foot of the centaur," but is nonetheless usually referred to by its Bayer designation Alpha Centauri. Another alternative name is Toliman from a Hebrew word meaning "the heretofore and the hereafter". It is also sometimes known as Bungula, possibly from the Latin word ungula meaning "hoof". It and Beta Centauri (which is close to Alpha Centauri in angular dist ...

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Alpha Centauri, Alpha Centauri - Names, Alpha Centauri - System components, Alpha Centauri - Possibility of planet formation, Alpha Centauri - Sky appearance from Alpha Centauri, Alpha Centauri - Apparent movement, Alpha Centauri - Alpha Centauri in fiction

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Sometimes Venus only grazes the Sun during a transit. In this case it is possible that in some areas of the Earth a full transit can be seen while in other regions there is only a partial transit (no second or fourth contact). The last transit of this type was on December 6th, 1631, while the next such transit will occur on December 13th, 2611. It is also possible that a transit of Venus can be seen in some parts of the world as a partial transit, while in others Venus misses the Sun. Such a transit last occurred on November 19th, 541BC, and th ...

See also:

Transit of Venus, Transit of Venus - Conjunctions of Venus with the Sun, Transit of Venus - Scientific interest in transits, Transit of Venus - Past and future transits, Transit of Venus - Grazing transits of Venus, Transit of Venus - Simultaneous transits, Transit of Venus - Cultural meaning

Read more here: » Transit of Venus: Encyclopedia II - Transit of Venus - Grazing transits of Venus