Auriga is one of the 88 modern constellations. Located north of the celestial equator, its name is the Latin word for “the charioteer”, associating it with various mythological beings, including Erichthonius and Myrtilus. Auriga is most prominent during winter evenings in the northern Hemisphere, along with the five other constellations that have stars in the Winter Hexagon asterism; because of its northern declination, Auriga is only visible in its entirety as far as 34° south. A large constellation, with an area of 657 square degrees, it is half the size of the largest constellation, Hydra, its brightest star, Capella, is an unusual multiple star system among the brightest stars in the night sky. Beta Aurigae is an interesting variable star in the constellation; because of its position near the winter Milky Way, Auriga has many bright open clusters in its borders, including M36, M37, M38, popular targets for amateur astronomers. In addition, it has one prominent nebula, the Flaming Star Nebula, associated with the variable star AE Aurigae.
In Chinese mythology, Auriga's stars were incorporated into several constellations, including the celestial emperors' chariots, made up of the modern constellation's brightest stars. Auriga is home to the radiant for the Aurigids, Zeta Aurigids, Delta Aurigids, the hypothesized Iota Aurigids; the first record of Auriga's stars was in Mesopotamia as a constellation called GAM, representing a scimitar or crook. However, this may have represented just the modern constellation as a whole. GAM in the MUL. APIN; the crook of Auriga shepherd. It was formed from most of the stars of the modern constellation. Bedouin astronomers created constellations that were groups of animals, where each star represented one animal; the stars of Auriga comprised a herd of goats, an association present in Greek mythology. The association with goats carried into the Greek astronomical tradition, though it became associated with a charioteer along with the shepherd. In Greek mythology, Auriga is identified as the mythological Greek hero Erichthonius of Athens, the chthonic son of Hephaestus, raised by the goddess Athena.
Erichthonius was credited to be the inventor of the quadriga, the four-horse chariot, which he used in the battle against the usurper Amphictyon, the event that made Erichthonius the king of Athens. His chariot was created in the image of the Sun's chariot, the reason Zeus placed him in the heavens; the Athenian hero dedicated himself to Athena and, soon after, Zeus raised him into the night sky in honor of his ingenuity and heroic deeds. Auriga, however, is sometimes described as Myrtilus, Hermes's son and the charioteer of Oenomaus; the association of Auriga and Myrtilus is supported by depictions of the constellation, which show a chariot. Myrtilus's chariot was destroyed in a race intended for suitors to win the heart of Oenomaus's daughter Hippodamia. Myrtilus earned his position in the sky when Hippodamia's successful suitor, killed him, despite his complicity in helping Pelops win her hand. After his death, Myrtilus's father Hermes placed him in the sky, yet another mythological association of Auriga is Theseus's son Hippolytus.
He was ejected from Athens after he refused the romantic advances of his stepmother Phaedra, who committed suicide as a result. He was revived by Asclepius. Regardless of Auriga's specific representation, it is that the constellation was created by the ancient Greeks to commemorate the importance of the chariot in their society. An incidental appearance of Auriga in Greek mythology is as the limbs of Medea's brother. In the myth of Jason and the Argonauts, as they journeyed home, Medea killed her brother and dismembered him, flinging the parts of his body into the sea, represented by the Milky Way; each individual star represents a different limb. Capella is associated with the mythological she-goat Amalthea, it forms an asterism with the stars Epsilon Aurigae, Zeta Aurigae, Eta Aurigae, the latter two of which are known as the Haedi. Though most associated with Amalthea, Capella has sometimes been associated with Amalthea's owner, a nymph; the myth of the nymph says that the goat's hideous appearance, resembling a Gorgon, was responsible for the Titans' defeat, because Zeus skinned the goat and wore it as his aegis.
The asterism containing the three goats had been a separate constellation. Before that, Capella was sometimes seen as its own constellation—by Pliny the Elder and Manilius—called Capra, Caper, or Hircus, all of which relate to its status as the "goat star". Zeta Aurigae and Eta Aurigae were first called the "Kids" by Cleostratus, an ancient Greek astronomer. Traditionally, illustrations of Auriga represent it as its driver; the charioteer has two kids under his left arm. However, depictions of Auriga have been inconsistent over the years; the reins in his right hand have been drawn as a whip, though Capella is always over his left shoulder and the Kids under his left arm. The 1488 atlas Hyginus deviated from this typical depiction by showing a four-wheeled cart driven by Auriga
Astronomy in China has a long history, beginning from the Shang Dynasty. Chinese star names categorized in the twenty-eight mansions have been found on oracle bones unearthed at Anyang, dating back to the middle Shang Dynasty, the mansion system's nucleus seems to have taken shape by the time of the ruler Wu Ding. Detailed records of astronomical observations began during the Warring States period and flourished from the Han period onward. Chinese astronomy was equatorial, centered as it was on close observation of circumpolar stars, was based on different principles from those prevailing in traditional Western astronomy, where heliacal risings and settings of zodiac constellations formed the basic ecliptic framework. Needham has described the ancient Chinese as the most persistent and accurate observers of celestial phenomena anywhere in the world before the Islamic astronomers; some elements of Indian astronomy reached China with the expansion of Buddhism after the Eastern Han Dynasty, but the most detailed incorporation of Indian astronomical thought occurred during the Tang Dynasty, when numerous Indian astronomers took up residence in the Chinese capital, Chinese scholars, such as the Tantric Buddhist monk and mathematician Yi Xing, mastered its system.
Islamic astronomers collaborated with their Chinese colleagues during the Yuan Dynasty, after a period of relative decline during the Ming Dynasty, astronomy was revitalized under the stimulus of Western cosmology and technology after the Jesuits established their missions. The telescope was introduced in the seventeenth century. In 1669, the Peking observatory was redesigned and refitted under the direction of Ferdinand Verbiest. Today, China continues to be active with many observatories and its own space program. One of the main functions was for the purpose of timekeeping; the Chinese used a lunisolar calendar, because the cycles of the Sun and the Moon are different, intercalation had to be done. The Chinese calendar was considered to be a symbol of a dynasty; as dynasties would rise and fall and astrologers of each period would prepare a new calendar to be made, with observations for that purpose. Astrological divination was an important part of astronomy. Astronomers took careful note of guest stars, which appeared among the fixed stars.
The supernova that created the Crab Nebula observed in 1054, now known as the SN 1054, is an example of a guest star observed by Chinese astronomers, recorded by the Arab astronomers, although it was not recorded by their European contemporaries. Ancient astronomical records of phenomena like comets and supernovae are sometimes used in modern astronomical studies. Indian astronomy reached China with the expansion of Buddhism during the Later Han. Further translation of Indian works on astronomy was completed in China by the Three Kingdoms era. However, the most detailed incorporation of Indian astronomy occurred only during the Tang Dynasty when a number of Chinese scholars—such as Yi Xing— were versed both in Indian and Chinese astronomy. A system of Indian astronomy was recorded in China as Jiuzhi-li, the author of, an Indian by the name of Qutan Xida—a translation of Devanagari Gotama Siddha—the director of the Tang dynasty's national astronomical observatory. During the 8th century, the astronomical table of sines by the Indian astronomer and mathematician, were translated into the Chinese astronomical and mathematical book of the Treatise on Astrology of the Kaiyuan Era, compiled in 718 CE during the Tang Dynasty.
The Kaiyuan Zhanjing was compiled by Gautama Siddha, an astronomer and astrologer born in Chang'an, whose family was from India. He was notable for his translation of the Navagraha calendar into Chinese. Gautama Siddha introduced Indian numerals with zero in 718 in China as a replacement of counting rods. In 3rd-century C. E, the Matanaga avadha was translated into Chinese.although the original is believed to date earlier. It gives the lengths of monthly shadows of a 12-inch gnomon, the standard parameter of Indian astronomy; the work mentions the 28 Indian nakshatras. In the beginning of the second century, Sardulakarnavadana was translated into Chinese several times, This work contains the usual Sanskrit names of the 28 nakshatras. Starting with krttika. From the 1st century onward Lalitavistara was translated into Chinese several times, it is in this work that the famous Buddhist centesimal-scale counting occurs during the dialogue between Prince Gautamaand and the mathematician Arjuna. The first series of counts ends with tallaksana, beyond which eight more ganana series are mentioned.
Atomic-scale counting is mentioned. The Mahaprajnaparamita Sastra was translated into Chinese by Kumarajiva in the early fifth century.16 The astronomical parameters mentioned in this translation are comparable to those given in the Vedanga Jyotisha. Indian system of numeration appeared in the Chinese work Ta PaoChi Ching, translated by Upasunya The Chinese translations of the following works are mentioned in the Sui Shu, or Official History of the Sui Dynasty: Po-lo-men Thien Wen Ching in 21 books. Po-lo-men Chieh-Chhieh Hsien-jen Thien Wen Shuo in 30 books. Po-lo-men Thien Ching in one book. Mo-teng-Chia Ching Huang-thu in onebook. Po-lo-men Suan Ching in three books. Po-lo-men Su
SIMBAD is an astronomical database of objects beyond the Solar System. It is maintained by the Centre de données astronomiques de France. SIMBAD was created by merging the Catalog of Stellar Identifications and the Bibliographic Star Index as they existed at the Meudon Computer Centre until 1979, expanded by additional source data from other catalogues and the academic literature; the first on-line interactive version, known as Version 2, was made available in 1981. Version 3, developed in the C language and running on UNIX stations at the Strasbourg Observatory, was released in 1990. Fall of 2006 saw the release of Version 4 of the database, now stored in PostgreSQL, the supporting software, now written in Java; as of 10 February 2017, SIMBAD contains information for 9,099,070 objects under 24,529,080 different names, with 327,634 bibliographical references and 15,511,733 bibliographic citations. The minor planet 4692 SIMBAD was named in its honour. Planetary Data System – NASA's database of information on SSSB, maintained by JPL and Caltech.
NASA/IPAC Extragalactic Database – a database of information on objects outside the Milky Way maintained by JPL. NASA Exoplanet Archive – an online astronomical exoplanet catalog and data service Bibcode SIMBAD, Strasbourg SIMBAD, Harvard
A giant star is a star with larger radius and luminosity than a main-sequence star of the same surface temperature. They lie above the main sequence on the Hertzsprung–Russell diagram and correspond to luminosity classes II and III; the terms giant and dwarf were coined for stars of quite different luminosity despite similar temperature or spectral type by Ejnar Hertzsprung about 1905. Giant stars have radii up to a few hundred times the Sun and luminosities between 10 and a few thousand times that of the Sun. Stars still more luminous than giants are referred to as hypergiants. A hot, luminous main-sequence star may be referred to as a giant, but any main-sequence star is properly called a dwarf no matter how large and luminous it is. A star becomes a giant after all the hydrogen available for fusion at its core has been depleted and, as a result, leaves the main sequence; the behaviour of a post-main-sequence star depends on its mass. For a star with a mass above about 0.25 solar masses, once the core is depleted of hydrogen it contracts and heats up so that hydrogen starts to fuse in a shell around the core.
The portion of the star outside the shell expands and cools, but with only a small increase in luminosity, the star becomes a subgiant. The inert helium core continues to grow and increase temperature as it accretes helium from the shell, but in stars up to about 10-12 M☉ it does not become hot enough to start helium burning. Instead, after just a few million years the core reaches the Schönberg–Chandrasekhar limit collapses, may become degenerate; this causes the outer layers to expand further and generates a strong convective zone that brings heavy elements to the surface in a process called the first dredge-up. This strong convection increases the transport of energy to the surface, the luminosity increases and the star moves onto the red-giant branch where it will stably burn hydrogen in a shell for a substantial fraction of its entire life; the core continues to gain mass and increase in temperature, whereas there is some mass loss in the outer layers. § 5.9. If the star's mass, when on the main sequence, was below 0.4 M☉, it will never reach the central temperatures necessary to fuse helium.
P. 169. It will therefore remain a hydrogen-fusing red giant until it runs out of hydrogen, at which point it will become a helium white dwarf. § 4.1, 6.1. According to stellar evolution theory, no star of such low mass can have evolved to that stage within the age of the Universe. In stars above about 0.4 M☉ the core temperature reaches 108 K and helium will begin to fuse to carbon and oxygen in the core by the triple-alpha process.§ 5.9, chapter 6. When the core is degenerate helium fusion begins explosively, but most of the energy goes into lifting the degeneracy and the core becomes convective; the energy generated by helium fusion reduces the pressure in the surrounding hydrogen-burning shell, which reduces its energy-generation rate. The overall luminosity of the star decreases, its outer envelope contracts again, the star moves from the red-giant branch to the horizontal branch. Chapter 6; when the core helium is exhausted, a star with up to about 8 M☉ has a carbon–oxygen core that becomes degenerate and starts helium burning in a shell.
As with the earlier collapse of the helium core, this starts convection in the outer layers, triggers a second dredge-up, causes a dramatic increase in size and luminosity. This is the asymptotic giant branch analogous to the red-giant branch but more luminous, with a hydrogen-burning shell contributing most of the energy. Stars only remain on the AGB for around a million years, becoming unstable until they exhaust their fuel, go through a planetary nebula phase, become a carbon–oxygen white dwarf. § 7.1–7.4. Main-sequence stars with masses above about 12 M☉ are very luminous and they move horizontally across the HR diagram when they leave the main sequence becoming blue giants before they expand further into blue supergiants, they start core-helium burning before the core becomes degenerate and develop smoothly into red supergiants without a strong increase in luminosity. At this stage they have comparable luminosities to bright AGB stars although they have much higher masses, but will further increase in luminosity as they burn heavier elements and become a supernova.
Stars in the 8-12 M☉ range have somewhat intermediate properties and have been called super-AGB stars. They follow the tracks of lighter stars through RGB, HB, AGB phases, but are massive enough to initiate core carbon burning and some neon burning, they form oxygen–magnesium–neon cores, which may collapse in an electron-capture supernova, or they may leave behind an oxygen–neon white dwarf. O class main sequence stars are highly luminous; the giant phase for such stars is a brief phase of increased size and luminosity before developing a supergiant spectral luminosity class. Type O giants may be more than a hundred thousand times as luminous as the sun, brighter than many supergiants. Classification is complex and difficult with small differences between luminosity classes and a continuous range of intermediate forms; the most massive stars develop giant or supergiant spectral features while still burning hydrogen in their cores, due to mixing of heavy elements to the surface and high luminosity which produces a powerful stellar wind and causes the star's atmosphere to expand.
A star whose initial mass is less than 0.25 M☉ will not become a giant star at all. For most of th
In astronomy, luminosity is the total amount of energy emitted per unit of time by a star, galaxy, or other astronomical object. As a term for energy emitted per unit time, luminosity is synonymous with power. In SI units luminosity is measured in joules per second or watts. Values for luminosity are given in the terms of the luminosity of the Sun, L⊙. Luminosity can be given in terms of the astronomical magnitude system: the absolute bolometric magnitude of an object is a logarithmic measure of its total energy emission rate, while absolute magnitude is a logarithmic measure of the luminosity within some specific wavelength range or filter band. In contrast, the term brightness in astronomy is used to refer to an object's apparent brightness: that is, how bright an object appears to an observer. Apparent brightness depends on both the luminosity of the object and the distance between the object and observer, on any absorption of light along the path from object to observer. Apparent magnitude is a logarithmic measure of apparent brightness.
The distance determined by luminosity measures can be somewhat ambiguous, is thus sometimes called the luminosity distance. In astronomy, luminosity is the amount of electromagnetic energy; when not qualified, the term "luminosity" means bolometric luminosity, measured either in the SI units, watts, or in terms of solar luminosities. A bolometer is the instrument used to measure radiant energy over a wide band by absorption and measurement of heating. A star radiates neutrinos, which carry off some energy, contributing to the star's total luminosity; the IAU has defined a nominal solar luminosity of 3.828×1026 W to promote publication of consistent and comparable values in units of the solar luminosity. While bolometers do exist, they cannot be used to measure the apparent brightness of a star because they are insufficiently sensitive across the electromagnetic spectrum and because most wavelengths do not reach the surface of the Earth. In practice bolometric magnitudes are measured by taking measurements at certain wavelengths and constructing a model of the total spectrum, most to match those measurements.
In some cases, the process of estimation is extreme, with luminosities being calculated when less than 1% of the energy output is observed, for example with a hot Wolf-Rayet star observed only in the infra-red. Bolometric luminosities can be calculated using a bolometric correction to a luminosity in a particular passband; the term luminosity is used in relation to particular passbands such as a visual luminosity of K-band luminosity. These are not luminosities in the strict sense of an absolute measure of radiated power, but absolute magnitudes defined for a given filter in a photometric system. Several different photometric systems exist; some such as the UBV or Johnson system are defined against photometric standard stars, while others such as the AB system are defined in terms of a spectral flux density. A star's luminosity can be determined from two stellar characteristics: size and effective temperature; the former is represented in terms of solar radii, R⊙, while the latter is represented in kelvins, but in most cases neither can be measured directly.
To determine a star's radius, two other metrics are needed: the star's angular diameter and its distance from Earth. Both can be measured with great accuracy in certain cases, with cool supergiants having large angular diameters, some cool evolved stars having masers in their atmospheres that can be used to measure the parallax using VLBI. However, for most stars the angular diameter or parallax, or both, are far below our ability to measure with any certainty. Since the effective temperature is a number that represents the temperature of a black body that would reproduce the luminosity, it cannot be measured directly, but it can be estimated from the spectrum. An alternative way to measure stellar luminosity is to measure the star's apparent brightness and distance. A third component needed to derive the luminosity is the degree of interstellar extinction, present, a condition that arises because of gas and dust present in the interstellar medium, the Earth's atmosphere, circumstellar matter.
One of astronomy's central challenges in determining a star's luminosity is to derive accurate measurements for each of these components, without which an accurate luminosity figure remains elusive. Extinction can only be measured directly if the actual and observed luminosities are both known, but it can be estimated from the observed colour of a star, using models of the expected level of reddening from the interstellar medium. In the current system of stellar classification, stars are grouped according to temperature, with the massive young and energetic Class O stars boasting temperatures in excess of 30,000 K while the less massive older Class M stars exhibit temperatures less than 3,500 K; because luminosity is proportional to temperature to the fourth power, the large variation in stellar temperatures produces an vaster variation in stellar luminosity. Because the luminosity depends on a high power of the stellar mass, high mass luminous stars have much shorter lifetimes; the most luminous stars are always young stars, no more than a few million years for the most extreme.
In the Hertzsprung–Russell diagram, the x-axis represents temperature or spectral type while the y-axis represents luminosity or magnitude. The vast majority of stars are found along the main sequence with blue Class O stars found at the top left of the chart while red Class M stars fall to the bottom right. Certain stars like Deneb and Betelgeuse are
A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called multiple star systems; these systems when more distant appear to the unaided eye as a single point of light, are revealed as multiple by other means. Research over the last two centuries suggests that half or more of visible stars are part of multiple star systems; the term double star is used synonymously with binary star. Optical doubles are so called because the two stars appear close together in the sky as seen from the Earth, their "doubleness" depends only on this optical effect. A double star can be revealed as optical by means of differences in their parallax measurements, proper motions, or radial velocities. Most known double stars have not been studied adequately to determine whether they are optical doubles or doubles physically bound through gravitation into a multiple star system. Binary star systems are important in astrophysics because calculations of their orbits allow the masses of their component stars to be directly determined, which in turn allows other stellar parameters, such as radius and density, to be indirectly estimated.
This determines an empirical mass-luminosity relationship from which the masses of single stars can be estimated. Binary stars are detected optically, 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 be detected by indirect techniques, such as spectroscopy or astrometry. If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other. If components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, these close binary systems can exchange mass, which may bring their evolution to stages that single stars cannot attain. Examples of binaries are Sirius, Cygnus X-1. Binary stars are common as the nuclei of many planetary nebulae, are the progenitors of both novae and type Ia supernovae; the term binary was first used in this context by Sir William Herschel in 1802, when he wrote: If, on the contrary, two stars should be situated near each other, at the same time so far insulated as not to be materially affected by the attractions of neighbouring stars, they will compose a separate system, remain united by the bond of their own mutual gravitation towards each other.
This should be called a real double star. By the modern definition, the term binary star is restricted to pairs of stars which revolve around a common center of mass. Binary stars which can be resolved with a telescope or interferometric methods are known as visual binaries. For most of the known visual binary stars one whole revolution has not been observed yet, they are observed to have travelled along a curved path or a partial arc; the more general term double star is used for pairs of stars which are seen to be close together in the sky. This distinction is made in languages other than English. Double stars may be binary systems or may be two stars that appear to be close together in the sky but have vastly different true distances from the Sun; the latter are termed optical optical pairs. Since the invention of the telescope, many pairs of double stars have been found. Early examples include Acrux. Mizar, in the Big Dipper, was observed to be double by Giovanni Battista Riccioli in 1650; the bright southern star Acrux, in the Southern Cross, was discovered to be double by Father Fontenay in 1685.
John Michell was the first to suggest that double stars might be physically attached to each other when he argued in 1767 that the probability that a double star was due to a chance alignment was small. William Herschel began observing double stars in 1779 and soon thereafter published catalogs of about 700 double stars. By 1803, he had observed changes in the relative positions in a number of double stars over the course of 25 years, concluded that they must be binary systems. Since this time, many more double stars have been measured; the Washington Double Star Catalog, a database of visual double stars compiled by the United States Naval Observatory, contains over 100,000 pairs of double stars, including optical doubles as well as binary stars. Orbits are known for only a few thousand of these double stars, most have not been ascertained to be either true binaries or optical double stars; this can be determined by observing the relative motion of the pairs. If the motion is part of an orbit, or if the stars have similar radial velocities and the difference in their proper motions is small compared to their common proper motion, the pair is physical.
One of the tasks that remains for visual observers of double stars is to obtain sufficient observations to prove or disprove gravitational connection. Binary stars are classified into four types accordi
A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so all of them disintegrate and never hit the Earth's surface. Intense or unusual meteor showers are known as meteor outbursts and meteor storms, which produce at least 1,000 meteors an hour, most notably from the Leonids; the Meteor Data Centre lists over 900 suspected meteor showers of which about 100 are well established. Several organizations point to viewing opportunities on the Internet; the first great meteor storm in the modern era was the Leonids of November 1833. One estimate is a peak rate of over one hundred thousand meteors an hour, but another, done as the storm abated, estimated in excess of two hundred thousand meteors during the 9 hours of storm, over the entire region of North America east of the Rocky Mountains.
American Denison Olmsted explained the event most accurately. After spending the last weeks of 1833 collecting information, he presented his findings in January 1834 to the American Journal of Science and Arts, published in January–April 1834, January 1836, he noted the shower was of short duration and was not seen in Europe, that the meteors radiated from a point in the constellation of Leo and he speculated the meteors had originated from a cloud of particles in space. Work continued, yet coming to understand the annual nature of showers though the occurrences of storms perplexed researchers; the actual nature of meteors was still debated during the XIX century. Meteors were conceived as an atmospheric phenomenon by many scientists until the Italian astronomer Giovanni Schiaparelli ascertained the relation between meteors and comets in his work "Notes upon the astronomical theory of the falling stars". In the 1890s, Irish astronomer George Johnstone Stoney and British astronomer Arthur Matthew Weld Downing, were the first to attempt to calculate the position of the dust at Earth's orbit.
They studied the dust ejected in 1866 by comet 55P/Tempel-Tuttle in advance of the anticipated Leonid shower return of 1898 and 1899. Meteor storms were anticipated, but the final calculations showed that most of the dust would be far inside of Earth's orbit; the same results were independently arrived at by Adolf Berberich of the Königliches Astronomisches Rechen Institut in Berlin, Germany. Although the absence of meteor storms that season confirmed the calculations, the advance of much better computing tools was needed to arrive at reliable predictions. In 1981 Donald K. Yeomans of the Jet Propulsion Laboratory reviewed the history of meteor showers for the Leonids and the history of the dynamic orbit of Comet Tempel-Tuttle. A graph from it was re-published in Sky and Telescope, it showed relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. This showed that the meteoroids are behind and outside the path of the comet, but paths of the Earth through the cloud of particles resulting in powerful storms were near paths of nearly no activity.
In 1985, E. D. Kondrat'eva and E. A. Reznikov of Kazan State University first identified the years when dust was released, responsible for several past Leonid meteor storms. In 1995, Peter Jenniskens predicted the 1995 Alpha Monocerotids outburst from dust trails. In anticipation of the 1999 Leonid storm, Robert H. McNaught, David Asher, Finland's Esko Lyytinen were the first to apply this method in the West. In 2006 Jenniskens published predictions for future dust trail encounters covering the next 50 years. Jérémie Vaubaillon continues to update predictions based on observations each year for the Institut de Mécanique Céleste et de Calcul des Éphémérides; because meteor shower particles are all traveling in parallel paths, at the same velocity, they will all appear to an observer below to radiate away from a single point in the sky. This radiant point is caused by the effect of perspective, similar to parallel railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks.
Meteor showers are always named after the constellation from which the meteors appear to originate. This "fixed point" moves across the sky during the night due to the Earth turning on its axis, the same reason the stars appear to march across the sky; the radiant moves from night to night against the background stars due to the Earth moving in its orbit around the sun. See IMO Meteor Shower Calendar 2017 for maps of drifting "fixed points." When the moving radiant is at the highest point it will reach in the observer's sky that night, the sun will be just clearing the eastern horizon. For this reason, the best viewing time for a meteor shower is slightly before dawn — a compromise between the maximum number of meteors available for viewing, the lightening sky which makes them harder to see. Meteor showers are named after the nearest constellation or bright star with a Greek or Roman letter assigned, close to the radiant position at the peak of the shower, whereby the grammatical declension of the Latin possessive form is replaced by "id" or "ids".
Hence, meteors radiating from near the star delta Aquarii are called delta Aquariids. The International Astronomical Union's Task Group on Meteor Shower Nomenclature and the IAU's Meteor Data Center keep track of meteor shower nomenclature and which showers are e