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
Ursa Major is a constellation in the northern sky, whose associated mythology dates back into prehistory. Its Latin name means "greater she-bear", standing as a reference to and in direct contrast with nearby Ursa Minor, the lesser bear. In antiquity, it was one of the original 48 constellations listed by Ptolemy, is now the third largest constellation of the 88 modern constellations. Ursa Major is known from the asterism of its main seven bright stars comprising the "Big Dipper", "the Wagon", "Charles's Wain" or "the Plough", with its stellar configuration mimicking the shape of the "Little Dipper"; the general constellation outline significantly features in numerous world cultures, is used as a symbol of the north. E.g. as the flag of Alaska. The asterism's two brightest stars, named Dubhe and Merak, can be used as the navigational pointer towards the place of the current northern pole star, Polaris in Ursa Minor. Ursa Major is visible throughout the year from most of the northern hemisphere, appears circumpolar above the mid-northern latitudes.
From southern temperate latitudes, the main asterism is invisible, but the southern parts of the constellation can still be viewed. Appearing in the northern sky, Ursa Major occupies a large area covering 1279.66 square degrees or 3.10% of the total sky, making it the third largest constellations in the night sky. Eugène Delporte in 1930, who set the official International Astronomical Union constellation boundaries, formed a 28-sided irregular polygon, which according to the equatorial coordinate system, stretches between the right ascension coordinates of 08h 08.3m and 14h 29.0m and the declination coordinates of +28.30° and +73.14°. Ursa Major borders eight other constellations: Draco to the north and northeast, Boötes to the east, Canes Venatici to the east and southeast, Coma Berenices to the southeast and Leo Minor to the south, Lynx to the southwest and Camelopardalis to the northwest; the three-letter constellation abbreviation'UMa' was adopted by the IAU in 1922. The "Big Dipper" is an asterism within Ursa Major composed of seven bright stars that together comprise one of the best-known patterns in the sky.
Like many of its common names allude to, its shape is said to resemble either a ladle, an agricultural plough or wagon. Starting with the "ladle" portion of the dipper and extending clockwise through the handle, these stars are the following: α Ursae Majoris, known by the Arabic name Dubhe, which at a magnitude of 1.79 is the 35th-brightest star in the sky and the second-brightest of Ursa Major. Β Ursae Majoris, called Merak, with a magnitude of 2.37. Γ Ursae Majoris, known as either Phecda or Phad, with a magnitude of 2.44. Δ Ursae Majoris, or Megrez, meaning "root of the tail," referring to its location as the intersection of the body and tail of the bear. Ε Ursae Majoris, known as Alioth, a name which refers not to a bear but to a "black horse," the name corrupted from the original and mis-assigned to the named Alcor, the naked-eye binary companion of Mizar. Alioth is the brightest star of Ursa Major and the 33rd-brightest in the sky, with a magnitude of 1.76. It is the brightest of the "peculiar A stars," magnetic stars whose chemical elements are either depleted or enhanced, appear to change as the star rotates.
Ζ Ursae Majoris, the second star in from the end of the handle of the Big Dipper, the constellation's fourth-brightest star. Mizar, which means "girdle," forms a famous double star, with its optical companion Alcor, the two of which were termed the "horse and rider" by the Arabs; the ability to resolve the two stars with the naked eye is quoted as a test of eyesight, although people with quite poor eyesight can see the two stars. Η Ursae Majoris, known as either Alkaid or Benetnash, both meaning the "end of the tail." With a magnitude of 1.85, Alkaid is the third-brightest star of Ursa Major. Except for Dubhe and Alkaid, the stars of the Big Dipper all have proper motions heading toward a common point in Sagittarius. A few other such stars have been identified, together they are called the Ursa Major Moving Group; the stars Merak and Dubhe are known as the "pointer stars" because they are helpful for finding Polaris known as the North Star or Pole Star. By visually tracing a line from Merak through Dubhe and continuing for 5 units, one's eye will land on Polaris indicating true north.
Another asterism known as the "Three Leaps of the Gazelle" is recognized in Arab culture, a series of three pairs of stars found along the southern border of the constellation. W Ursae Majoris is the prototype of a class of contact binary variable stars, ranges between 7.75m and 8.48m. 47 Ursae Majoris is a Sun-like star with a three-planet system. 47 Ursae Majoris b, discovered in 1996, orbits every 1078 days and is 2.53 times the mass of Jupiter. 47 Ursae Majoris c, discovered in 2001, orbits every 2391 days and is 0.54 times the
Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, but two-and-a-half times that of all the other planets in the Solar System combined. Jupiter and Saturn are gas giants. Jupiter has been known to astronomers since antiquity, it is named after the Roman god Jupiter. When viewed from Earth, Jupiter can reach an apparent magnitude of −2.94, bright enough for its reflected light to cast shadows, making it on average the third-brightest natural object in the night sky after the Moon and Venus. Jupiter is composed of hydrogen with a quarter of its mass being helium, though helium comprises only about a tenth of the number of molecules, it may have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rapid rotation, the planet's shape is that of an oblate spheroid; the outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries.
A prominent result is the Great Red Spot, a giant storm, known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a powerful magnetosphere. Jupiter has 79 known moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a diameter greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and by the Galileo orbiter. In late February 2007, Jupiter was visited by the New Horizons probe, which used Jupiter's gravity to increase its speed and bend its trajectory en route to Pluto; the latest probe to visit the planet is Juno, which entered into orbit around Jupiter on July 4, 2016. Future targets for exploration in the Jupiter system include the probable ice-covered liquid ocean of its moon Europa. Astronomers have discovered nearly 500 planetary systems with multiple planets.
These systems include a few planets with masses several times greater than Earth's, orbiting closer to their star than Mercury is to the Sun, sometimes Jupiter-mass gas giants close to their star. Earth and its neighbor planets may have formed from fragments of planets after collisions with Jupiter destroyed those super-Earths near the Sun; as Jupiter came toward the inner Solar System, in what theorists call the grand tack hypothesis, gravitational tugs and pulls occurred causing a series of collisions between the super-Earths as their orbits began to overlap. Researchers from Lund University found that Jupiter's migration went on for around 700,000 years, in a period 2-3 million years after the celestial body started its life as an ice asteroid far from the sun; the journey inwards in the solar system followed a spiraling course in which Jupiter continued to circle around the sun, albeit in an tight path. The reason behind the actual migration relates to gravitational forces from the surrounding gases in the solar system.
Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including Earth. Jupiter is composed of gaseous and liquid matter, it is the largest of hence its largest planet. It has a diameter of 142,984 km at its equator; the average density of Jupiter, 1.326 g/cm3, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiter's upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules. A helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiter's atmosphere is 75% hydrogen and 24% helium by mass, with the remaining one percent of the mass consisting of other elements; the atmosphere contains trace amounts of methane, water vapor and silicon-based compounds. There are traces of carbon, hydrogen sulfide, oxygen and sulfur; the outermost layer of the atmosphere contains crystals of frozen ammonia.
The interior contains denser materials—by mass it is 71% hydrogen, 24% helium, 5% other elements. Through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have been found; the atmospheric proportions of hydrogen and helium are close to the theoretical composition of the primordial solar nebula. Neon in the upper atmosphere only consists of 20 parts per million by mass, about a tenth as abundant as in the Sun. Helium is depleted to about 80% of the Sun's helium composition; this depletion is a result of precipitation of these elements into the interior of the planet. Based on spectroscopy, Saturn is thought to be similar in composition to Jupiter, but the other giant planets Uranus and Neptune have less hydrogen and helium and more ices and are thus now termed ice giants. Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined—this is so massive that its barycenter with the Sun lies above the Sun's surface at 1.068 solar radii from the Sun's center.
Jupiter is much larger than Earth and less dense: its volume is that of about 1,321 Earths, but it is only 318 times as massive. Jupiter's radius is about 1/10 the radius of the Sun, its mass is 0.001 times the mass of the Sun, so the densities of the two bodies are similar. A "Jupiter mass" is used as a u
The apparent magnitude of an astronomical object is a number, a measure of its brightness as seen by an observer on Earth. The magnitude scale is logarithmic. A difference of 1 in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The brighter an object appears, the lower its magnitude value, with the brightest astronomical objects having negative apparent magnitudes: for example Sirius at −1.46. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry. Apparent magnitudes are used to quantify the brightness of sources at ultraviolet and infrared wavelengths. An apparent magnitude is measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V filter band would be denoted either as mV or simply as V, as in "mV = 15" or "V = 15" to describe a 15th-magnitude object; the scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes.
The brightest stars in the night sky were said to be of first magnitude, whereas the faintest were of sixth magnitude, the limit of human visual perception. Each grade of magnitude was considered twice the brightness of the following grade, although that ratio was subjective as no photodetectors existed; this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest and is believed to have originated with Hipparchus. In 1856, Norman Robert Pogson formalized the system by defining a first magnitude star as a star, 100 times as bright as a sixth-magnitude star, thereby establishing the logarithmic scale still in use today; this implies that a star of magnitude m is about 2.512 times as bright as a star of magnitude m + 1. This figure, the fifth root of 100, became known as Pogson's Ratio; the zero point of Pogson's scale was defined by assigning Polaris a magnitude of 2. Astronomers discovered that Polaris is variable, so they switched to Vega as the standard reference star, assigning the brightness of Vega as the definition of zero magnitude at any specified wavelength.
Apart from small corrections, the brightness of Vega still serves as the definition of zero magnitude for visible and near infrared wavelengths, where its spectral energy distribution approximates that of a black body for a temperature of 11000 K. However, with the advent of infrared astronomy it was revealed that Vega's radiation includes an Infrared excess due to a circumstellar disk consisting of dust at warm temperatures. At shorter wavelengths, there is negligible emission from dust at these temperatures. However, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the magnitude scale was extrapolated to all wavelengths on the basis of the black-body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance for the zero magnitude point, as a function of wavelength, can be computed. Small deviations are specified between systems using measurement apparatuses developed independently so that data obtained by different astronomers can be properly compared, but of greater practical importance is the definition of magnitude not at a single wavelength but applying to the response of standard spectral filters used in photometry over various wavelength bands.
With the modern magnitude systems, brightness over a wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30; the brightness of Vega is exceeded by four stars in the night sky at visible wavelengths as well as the bright planets Venus and Jupiter, these must be described by negative magnitudes. For example, the brightest star of the celestial sphere, has an apparent magnitude of −1.4 in the visible. Negative magnitudes for other bright astronomical objects can be found in the table below. Astronomers have developed other photometric zeropoint systems as alternatives to the Vega system; the most used is the AB magnitude system, in which photometric zeropoints are based on a hypothetical reference spectrum having constant flux per unit frequency interval, rather than using a stellar spectrum or blackbody curve as the reference. The AB magnitude zeropoint is defined such that an object's AB and Vega-based magnitudes will be equal in the V filter band.
As the amount of light received by a telescope is reduced by transmission through the Earth's atmosphere, any measurement of apparent magnitude is corrected for what it would have been as seen from above the atmosphere. The dimmer an object appears, the higher the numerical value given to its apparent magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of 100. Therefore, the apparent magnitude m, in the spectral band x, would be given by m x = − 5 log 100 , more expressed in terms of common logarithms as m x
Boötes is a constellation in the northern sky, located between 0° and +60° declination, 13 and 16 hours of right ascension on the celestial sphere. The name comes from the Greek Βοώτης, Boōtēs, meaning “herdsman” or “plowman”. One of the 48 constellations described by the 2nd-century astronomer Ptolemy, Boötes is now one of the 88 modern constellations, it contains the fourth-brightest star in the orange giant Arcturus. Epsilon Bootis, or Izar, is a colourful multiple star popular with amateur astronomers. Boötes is home to many other bright stars, including eight above the fourth magnitude and an additional 21 above the fifth magnitude, making a total of 29 stars visible to the naked eye. In ancient Babylon, the stars of Boötes were known as SHU. PA, they were depicted as the god Enlil, the leader of the Babylonian pantheon and special patron of farmers. Boötes may have been represented by the foreleg constellation in ancient Egypt. According to this interpretation, the constellation depicts the shape of an animal foreleg.
The name Boötes was first used by Homer in his Odyssey as a celestial reference point for navigation, described as "late-setting" or "slow to set", translated as the "Plowman". Whom Boötes is supposed to represent in Greek mythology is not clear. According to one version, he was a son of Demeter, twin brother of Plutus, a plowman who drove the oxen in the constellation Ursa Major; this is corroborated by the constellation's name, which itself means "ox-driver" or "herdsman." The ancient Greeks saw. This influenced the name's etymology, derived from the Greek for "noisy" or "ox-driver". Another myth associated with Boötes relates that he invented the plow and was memorialized for his ingenuity as a constellation. Another myth associated with Boötes by Hyginus is that of Icarius, schooled as a grape farmer and winemaker by Dionysus. Icarius made wine so strong that those who drank it appeared poisoned, which caused shepherds to avenge their poisoned friends by killing Icarius. Maera, Icarius' dog, brought his daughter Erigone to her father's body, whereupon both she and the dog committed suicide.
Zeus chose to honor all three by placing them in the sky as constellations: Icarius as Boötes, Erigone as Virgo, Maera as Canis Major or Canis Minor. Following another reading, the constellation is identified with Arcas and referred to as Arcas and Arcturus, son of Zeus and Callisto. Arcas was brought up by his maternal grandfather Lycaon, to whom one day Zeus had a meal. To verify that the guest was the king of the gods, Lycaon killed his grandson and prepared a meal made from his flesh. Zeus noticed and became angry, transforming Lycaon into a wolf and giving life back to his son. In the meantime Callisto had been transformed into a she-bear by Zeus's wife Hera, angry at Zeus's infidelity; this is corroborated by the Greek name for Boötes, which means "Bear Watcher". Callisto, in the form of a bear was killed by her son, out hunting. Zeus rescued her, taking her into the sky where she became Ursa Major, "the Great Bear". Arcturus, the name of the constellation's brightest star, comes from the Greek word meaning "guardian of the bear".
Sometimes Arcturus is depicted as leading the hunting dogs of nearby Canes Venatici and driving the bears of Ursa Major and Ursa Minor. Several former constellations were formed from stars now included in Boötes. Quadrans Muralis, the Quadrant, was a constellation created near Beta Boötis from faint stars, it was designated in 1795 by Jérôme Lalande, an astronomer who used a quadrant to perform detailed astronometric measurements. Lalande worked with others to predict the 1758 return of Halley's Comet. Quadrans Muralis was formed from the stars of eastern Boötes, western Hercules, Draco, it was called Le Mural by Jean Fortin in his 1795 Atlas Céleste. The constellation was quite faint, with its brightest stars reaching the 5th magnitude. Mons Maenalus, representing the Maenalus mountains, was created by Johannes Hevelius in 1687 at the foot of the constellation's figure; the mountain was named for the son of Maenalus. The mountain, one of Diana's hunting grounds, was holy to Pan; the stars of Boötes were incorporated into many different Chinese constellations.
Arcturus was part of the most prominent of these, variously designated as the celestial king's throne or the Blue Dragon's horn. Arcturus was given such importance in Chinese celestial mythology because of its status marking the beginning of the lunar calendar, as well as its status as the brightest star in the northern night sky. Two constellations flanked Daijiao: Yousheti to Zuosheti to the left. Zuosheti was formed from modern Zeta, Pi Boötis, while Yousheti was formed from modern Eta and Upsilon Boötis. Dixi, the Emperor's ceremonial banquet mat, was north of Arcturus, consisting of the stars 12, 11, 9 Boötis. Another northern constellation was Qigong, the Seven Dukes, which straddled the Boötes-Hercules border, it included either Delta Boötis or Beta Boötis as its terminus. The other Chinese constellations made up of the stars of Boötes existed in the modern constellation's north. Tianqiang, the spear, was formed from Iota and Theta Boötis. There were two
Serpens is a constellation of the northern hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations defined by the International Astronomical Union, it is unique among the modern constellations in being split into two non-contiguous parts, Serpens Caput to the west and Serpens Cauda to the east. Between these two halves lies the constellation of Ophiuchus, the "Serpent-Bearer". In figurative representations, the body of the serpent is represented as passing behind Ophiuchus between Mu Serpentis in Serpens Caput and Nu Serpentis in Serpens Cauda; the brightest star in Serpens is the red giant star Alpha Serpentis, or Unukalhai, in Serpens Caput, with an apparent magnitude of 2.63. Located in Serpens Caput are the naked-eye globular cluster Messier 5 and the naked-eye variables R Serpentis and Tau4 Serpentis. Notable extragalactic objects include one of the densest galaxy clusters known. Part of the Milky Way's galactic plane passes through Serpens Cauda, therefore rich in galactic deep-sky objects, such as the Eagle Nebula and its associated star cluster Messier 16.
The nebula measures 70 light-years by 50 light-years and contains the Pillars of Creation, three dust clouds that became famous for the image taken by the Hubble Space Telescope. Other striking objects include the Red Square Nebula, one of the few objects in astronomy to take on a square shape. In Greek mythology, Serpens represents a snake held by the healer Asclepius. Represented in the sky by the constellation Ophiuchus, Asclepius once killed a snake, but the animal was subsequently resurrected after a second snake placed a revival herb on it before its death; as snakes shed their skin every year, they were known as the symbol of rebirth in ancient Greek society, legend says Asclepius would revive dead humans using the same technique he witnessed. Although this is the logic for Serpens' presence with Ophiuchus, the true reason is still not known. Sometimes, Serpens was depicted as coiling around Ophiuchus, but the majority of atlases showed Serpens passing either behind Ophiuchus' body or between his legs.
In some ancient atlases, the constellations Serpens and Ophiuchus were depicted as two separate constellations, although more they were shown as a single constellation. One notable figure to depict Serpens separately was Johann Bayer; when Eugène Delporte established modern constellation boundaries in the 1920s, he elected to depict the two separately. However, this posed the problem of how to disentangle the two constellations, with Deporte deciding to split Serpens into two areas—the head and the tail—separated by the continuous Ophiuchus; these two areas became known as Serpens Caput and Serpens Cauda, caput being the Latin word for head and cauda the Latin word for tail. In Chinese astronomy, most of the stars of Serpens represented part of a wall surrounding a marketplace, known as Tianshi, in Ophiuchus and part of Hercules. Serpens contains a few Chinese constellations. Two stars in the tail represented part of the tower with the market office. Another star in the tail represented jewel shops.
One star in the head marked the crown prince's wet nurse, or sometimes rain. There were two "serpent" constellations in Babylonian astronomy, known as Bašmu, it appears that Mušḫuššu was depicted as a hybrid of a dragon, a lion and a bird, loosely corresponded to Hydra. Bašmu was a horned serpent and corresponds to the Ὄφις constellation of Eudoxus of Cnidus on which the Ὄφις of Ptolemy is based. Serpens is the only one of the 88 modern constellations to be split into two disconnected regions in the sky: Serpens Caput and Serpens Cauda; the constellation is unusual in that it depends on another constellation for context. Serpens Caput is bordered by Libra to the south, Virgo and Boötes to the east, Corona Borealis to the north, Ophiuchus and Hercules to the west. Covering 636.9 square degrees total, it ranks 23rd of the 88 constellations in size. It appears prominently in both the northern and southern skies during the Northern Hemisphere's summer, its main asterism consists of 11 stars, 108 stars in total are brighter than magnitude 6.5, the traditional limit for naked-eye visibility.
Serpens Caput's boundaries, as set by Eugène Delporte in 1930, are defined by a 15-sided polygon, while Serpens Cauda's are defined by a 25-sided polygon. In the equatorial coordinate system, the right ascension coordinates of Serpens Caput's borders lie between 15h 10.4m and 16h 22.5m, while the declination coordinates are between 25.66° and −03.72°. Serpens Cauda's boundaries lie between right ascensions of 17h 16.9m and 18h 58.3m and declinations of 06.42° and −16.14°. The International Astronomical Union adopted the three-letter abbreviation "Ser" for the constellation in 1922. Marking the heart of the serpent is the constellation's brightest star, Alpha Serpentis. Traditionally called Unukalhai, is a red giant of spectral type K2III located 23 parsecs distant with a visual magnitude of 2.630 ± 0.009, meaning it can be seen with the naked eye in
A super-Earth is an extrasolar planet with a mass higher than Earth's, but below those of the Solar System's ice giants and Neptune, which are 15 and 17 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, so does not imply anything about the surface conditions or habitability; the alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, as suggested by MIT professor Sara Seager, although "mini-Neptunes" is a more common term. In general, super-Earths are defined by their masses, the term does not imply temperatures, orbital properties, habitability, or environments. While sources agree on an upper bound of 10 Earth masses, the lower bound varies from 1 or 1.9 to 5, with various other definitions appearing in the popular media. The term "super-Earth" is used by astronomers to refer to planets bigger than Earth-like planets, but smaller than mini-Neptunes; this definition was made by the Kepler Mission. Some authors further suggest that the term Super-Earth might be limited to rocky planets without a significant atmosphere, or planets that have not just atmospheres but solid surfaces or oceans with a sharp boundary between liquid and atmosphere, which the four giant planets in the Solar System do not have.
Planets above 10 Earth masses are termed massive solid planets/mega-Earths or gas giant planets depending on whether they are rock and ice or gas. The first super-Earths were discovered by Aleksander Wolszczan and Dale Frail around the pulsar PSR B1257+12 in 1992; the two outer planets of the system have masses four times Earth—too small to be gas giants. The first super-Earth around a main-sequence star was discovered by a team under Eugenio Rivera in 2005, it received the designation Gliese 876 d. It has an estimated mass of 7.5 Earth masses and a short orbital period of just about 2 days. Due to the proximity of Gliese 876 d to its host star, it may have a surface temperature of 430–650 kelvins and be too hot to support liquid water. In April 2007, a team headed by Stéphane Udry based in Switzerland announced the discovery of two new super-Earths within the Gliese 581 planetary system, both on the edge of the habitable zone around the star where liquid water may be possible on the surface.
With Gliese 581c having a mass of at least 5 Earth masses and a distance from Gliese 581 of 0.073 astronomical units, it is on the "warm" edge of the habitable zone around Gliese 581 with an estimated mean temperature of −3 degrees Celsius with an albedo comparable to Venus and 40 degrees Celsius with an albedo comparable to Earth. Subsequent research suggested Gliese 581c had suffered a runaway greenhouse effect like Venus. Two further super-Earths were discovered in 2006: OGLE-2005-BLG-390Lb with a mass of 5.5 Earth masses, found by gravitational microlensing, HD 69830 b with a mass of 10 Earth masses. The smallest super-Earth found as of 2008 was MOA-2007-BLG-192Lb; the planet was announced by astrophysicist David P. Bennett for the international MOA collaboration on June 2, 2008; this planet has 3.3 Earth masses and orbits a brown dwarf. It was detected by gravitational microlensing. In June 2008, European researchers announced the discovery of three super-Earths around the star HD 40307, a star, only less massive than our Sun.
The planets have at least the following minimum masses: 4.2, 6.7, 9.4 times Earth's. The planets were detected by the radial velocity method by the HARPS in Chile. In addition, the same European research team announced a planet 7.5 times the mass of Earth orbiting the star HD 181433. This star has a Jupiter-like planet that orbits every three years. Planet COROT-7b, with a mass estimated at 4.8 Earth masses and an orbital period of only 0.853 days, was announced on 3 February 2009. The density estimate obtained for COROT-7b points to a composition including rocky silicate minerals, similar to the four inner planets of the Solar System, a new and significant discovery. COROT-7b, discovered right after HD 7924 b, is the first super-Earth discovered that orbits a main sequence star, G class or larger; the discovery of Gliese 581e with a minimum mass of 1.9 Earth masses was announced on 21 April 2009. It was at the time the smallest extrasolar planet discovered around a normal star and the closest in mass to Earth.
Being at an orbital distance of just 0.03 AU and orbiting its star in just 3.15 days, it is not in the habitable zone, may have 100 times more tidal heating than Jupiter's volcanic satellite Io. A planet found in December 2009, GJ 1214 b, is 2.7 times as large as Earth and orbits a star much smaller and less luminous than our Sun. "This planet does have liquid water," said David Charbonneau, a Harvard professor of astronomy and lead author of an article on the discovery. However, interior models of this planet suggest that under most conditions it does not have liquid water. By November 2009, a total of 30 super-Earths had been discovered, 24 of which were first observed by HARPS. Discovered on 5 January 2010, a planet HD 156668 b with a minimum mass of 4.15 Earth masses, is the least massive planet detected by the radial velocity method. The only confirmed radial velocity planet smaller than this planet is Gliese 581e at 1.9 Earth masses. On 24 August, astronomers using