Perseus is a constellation in the northern sky, being named after the Greek mythological hero Perseus. It is one of the 48 ancient constellations listed by the 2nd-century astronomer Ptolemy, among the 88 modern constellations defined by the International Astronomical Union, it is located near several other constellations named after ancient Greek legends surrounding Perseus, including Andromeda to the west and Cassiopeia to the north. Perseus is bordered by Aries and Taurus to the south, Auriga to the east, Camelopardalis to the north, Triangulum to the west; some star atlases during the early 19th century depicted Perseus holding the disembodied head of Medusa, whose asterism was named together as Perseus et Caput Medusae, this never came into popular usage. The galactic plane of the Milky Way passes through Perseus, whose brightest star is the yellow-white supergiant Alpha Persei, which shines at magnitude 1.79. It and many of the surrounding stars are members of an open cluster known as the Alpha Persei Cluster.
The best-known star, however, is Algol, linked with ominous legends because of its variability, noticeable to the naked eye. Rather than being an intrinsically variable star, it is an eclipsing binary. Other notable star systems in Perseus include X Persei, a binary system containing a neutron star, GK Persei, a nova that peaked at magnitude 0.2 in 1901. The Double Cluster, comprising two open clusters quite near each other in the sky, was known to the ancient Chinese; the constellation gives its name to the Perseus cluster, a massive galaxy cluster located 250 million light-years from Earth. It hosts the radiant of the annual Perseids meteor shower—one of the most prominent meteor showers in the sky; the constellation of Perseus may be derived from the Babylonian Old Man constellation associated with East in the MUL. APIN—an astronomical compilation dating to around 1000 BCE. In Greek mythology, Perseus was the son of Danaë, sent by King Polydectes to bring the head of Medusa the Gorgon — whose visage caused all who gazed upon her to turn to stone.
Perseus slew Medusa in her sleep, Pegasus and Chrysaor appeared from her body. Perseus continued to the realm of Cepheus whose daughter Andromeda was to be sacrificed to Cetus the sea monster. Perseus rescued Andromeda from the monster by killing it with his diamond sword, he turned Polydectes and his followers to stone with Medusa's head and appointed Dictys the fisherman king. Perseus and Andromeda had six children. In the sky, Perseus lies near the constellations Andromeda, Cassiopeia and Pegasus. Four Chinese constellations are contained in the area of the sky identified with Perseus in the West. Tiānchuán, the Celestial Boat, was the third paranatellon of the third house of the White Tiger of the West, representing the boats that Chinese people were reminded to build in case of a catastrophic flood season. Incorporating stars from the northern part of the constellation, it contained Mu, Psi, Alpha and Eta Persei. Jīshuǐ, the Swollen Waters, was the fourth paranatellon of the aforementioned house, representing the potential of unusually high floods during the end of August and beginning of September at the beginning of the flood season.
Lambda and Mu Persei lay within it. Dàlíng, the Great Trench, was the fifth paranatellon of that house, representing the trenches where criminals executed en masse in August were interred, it was formed by Kappa, Rho, 24, 17 and 15 Persei. The pile of corpses prior to their interment was represented by Jīshī, the sixth paranatellon of the house; the Double Cluster, h and Chi Persei, had special significance in Chinese astronomy. In Polynesia, Perseus was not recognized as a separate constellation. Algol may have been named Matohi by the Māori people, but the evidence for this identification is disputed. Matohi came into conflict with Tangaroa-whakapau over which of them should appear in the sky, the outcome affecting the tides, it matches the Maori description of a blue-white star near Aldebaran but does not disappear as the myth would indicate. Perseus is bordered by Aries and Taurus to the south, Auriga to the east and Cassiopeia to the north, Andromeda and Triangulum to the west. Covering 615 square degrees, it ranks twenty-fourth of the 88 constellations in size.
It appears prominently in the northern sky during the Northern Hemisphere's spring. Its main asterism consists of 19 stars; the constellation's boundaries, as set by Eugène Delporte in 1930, are defined by a 26-sided polygon. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 01h 29.1m and 04h 51.2m, while the declination coordinates are between 30.92° and 59.11°. The International Astronomical Union adopted the three-letter abbreviation "Per" for the constellation in 1922. Algol known by its Bayer designation Beta Persei, is the best-known star in Perseus. Representing the head of the Gorgon Medusa in Greek mythology, it was called Horus in Egyptian mythology and Rosh ha Satan in Hebrew. Located 92.8 light-years from Earth, it varies in apparent magnitude from a minimum of 3.5 to a maximum of 2.3 over a period of 2.867 days. The star system is the prototype of a group of eclipsing binary stars named Algol variables, though it has a third member to make up what is a triple star system.
The brightest compo
NGC 505 is a lenticular galaxy 234 million light-years away from Earth in the constellation of Pisces. It was discovered by German astronomer Albert Marth on October 1, 1864. Lenticular galaxy List of NGC objects Pisces NGC 505 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images SEDS
Hipparchus of Nicaea was a Greek astronomer and mathematician. He is considered the founder of trigonometry but is most famous for his incidental discovery of precession of the equinoxes. Hipparchus was born in Nicaea and died on the island of Rhodes, Greece, he is known to have been a working astronomer at least from 162 to 127 BC. Hipparchus is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity, he was the first whose accurate models for the motion of the Sun and Moon survive. For this he made use of the observations and the mathematical techniques accumulated over centuries by the Babylonians and by Meton of Athens, Aristyllus, Aristarchus of Samos and Eratosthenes, among others, he developed trigonometry and constructed trigonometric tables, he solved several problems of spherical trigonometry. With his solar and lunar theories and his trigonometry, he may have been the first to develop a reliable method to predict solar eclipses.
His other reputed achievements include the discovery and measurement of Earth's precession, the compilation of the first comprehensive star catalog of the western world, the invention of the astrolabe of the armillary sphere, which he used during the creation of much of the star catalogue. There is a strong tradition that Hipparchus was born in Nicaea, in the ancient district of Bithynia, in what today is the country Turkey; the exact dates of his life are not known, but Ptolemy attributes astronomical observations to him in the period from 147–127 BC, some of these are stated as made in Rhodes. His birth date was calculated by Delambre based on clues in his work. Hipparchus must have lived some time after 127 BC because he analyzed and published his observations from that year. Hipparchus obtained information from Alexandria as well as Babylon, but it is not known when or if he visited these places, he is believed to have died on the island of Rhodes, where he seems to have spent most of his life.
It is not known what Hipparchus's economic means were nor how he supported his scientific activities. His appearance is unknown: there are no contemporary portraits. In the 2nd and 3rd centuries coins were made in his honour in Bithynia that bear his name and show him with a globe. Little of Hipparchus's direct work survives into modern times. Although he wrote at least fourteen books, only his commentary on the popular astronomical poem by Aratus was preserved by copyists. Most of what is known about Hipparchus comes from Strabo's Geography and Pliny's Natural History in the 1st century. Hipparchus was amongst the first to calculate a heliocentric system, but he abandoned his work because the calculations showed the orbits were not circular as believed to be mandatory by the science of the time. Although a contemporary of Hipparchus', Seleucus of Seleucia, remained a proponent of the heliocentric model, Hipparchus' rejection of heliocentrism, supported by ideas from Aristotle, remained dominant for nearly 2000 years until Copernican heliocentrism turned the tide of the debate.
Hipparchus's only preserved work is Τῶν Ἀράτου καὶ Εὐδόξου φαινομένων ἐξήγησις. This is a critical commentary in the form of two books on a popular poem by Aratus based on the work by Eudoxus. Hipparchus made a list of his major works, which mentioned about fourteen books, but, only known from references by authors, his famous star catalog was incorporated into the one by Ptolemy, may be perfectly reconstructed by subtraction of two and two thirds degrees from the longitudes of Ptolemy's stars. The first trigonometric table was compiled by Hipparchus, now known as "the father of trigonometry". Hipparchus was in the international news in 2005, when it was again proposed that the data on the celestial globe of Hipparchus or in his star catalog may have been preserved in the only surviving large ancient celestial globe which depicts the constellations with moderate accuracy, the globe carried by the Farnese Atlas. There are a variety of mis-steps in the more ambitious 2005 paper, thus no specialists in the area accept its publicized speculation.
Lucio Russo has said that Plutarch, in his work On the Face in the Moon, was reporting some physical theories that we consider to be Newtonian and that these may have come from Hipparchus. According to one book review, both of these claims have been rejected by other scholars. A line in Plutarch's Table Talk states that Hipparchus counted 103049 compound propositions that can be formed from ten simple propositions. 103049 is the tenth Schröder–Hipparchus number, which counts the number of ways of adding one or more pairs of parentheses around consecutive subsequences of two or more items in any sequence of ten symbols. This has led to speculation that Hipparchus knew about enumerative combinatorics, a field of mathematics that developed independently in modern mathematics. Earlier Greek astronomers and mathematicians were influenced by Babylonian astronomy to some extent, for instance the period relations of the Metonic cycle and Saros cycle may have come from Babylonian sources (see "Babylonian astron
The Milky Way is the galaxy that contains our Solar System. The name describes the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye; the term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος. From Earth, the Milky Way appears as a band. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610; until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies; the Milky Way is a barred spiral galaxy with a diameter between 200,000 light-years. It is estimated to contain 100 -- more than 100 billion planets; the Solar System is located at a radius of 26,490 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust.
The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic center is an intense radio source known as Sagittarius A*, assumed to be a supermassive black hole of 4.100 million solar masses. Stars and gases at a wide range of distances from the Galactic Center orbit at 220 kilometers per second; the constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter"; the rotational period is about 240 million years at the radius of the Sun. The Milky Way as a whole is moving at a velocity of 600 km per second with respect to extragalactic frames of reference; the oldest stars in the Milky Way are nearly as old as the Universe itself and thus formed shortly after the Dark Ages of the Big Bang. The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, itself a component of the Laniakea Supercluster.
The Milky Way is visible from Earth as a hazy band of white light, some 30° wide, arching across the night sky. In night sky observing, although all the individual naked-eye stars in the entire sky are part of the Milky Way, the term “Milky Way” is limited to this band of light; the light originates from the accumulation of unresolved stars and other material located in the direction of the galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, are areas where interstellar dust blocks light from distant stars; the area of sky that the Milky Way obscures is called the Zone of Avoidance. The Milky Way has a low surface brightness, its visibility can be reduced by background light, such as light pollution or moonlight. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the Milky Way to be visible. It should be visible if the limiting magnitude is +5.1 or better and shows a great deal of detail at +6.1. This makes the Milky Way difficult to see from brightly lit urban or suburban areas, but prominent when viewed from rural areas when the Moon is below the horizon.
Maps of artificial night sky brightness show that more than one-third of Earth's population cannot see the Milky Way from their homes due to light pollution. As viewed from Earth, the visible region of the Milky Way's galactic plane occupies an area of the sky that includes 30 constellations; the Galactic Center lies in the direction of Sagittarius. From Sagittarius, the hazy band of white light appears to pass around to the galactic anticenter in Auriga; the band continues the rest of the way around the sky, back to Sagittarius, dividing the sky into two equal hemispheres. The galactic plane is inclined by about 60° to the ecliptic. Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic, relative to the galactic plane; the north galactic pole is situated at right ascension 12h 49m, declination +27.4° near β Comae Berenices, the south galactic pole is near α Sculptoris.
Because of this high inclination, depending on the time of night and year, the arch of the Milky Way may appear low or high in the sky. For observers from latitudes 65° north to 65° south, the Milky Way passes directly overhead twice a day; the Milky Way is the second-largest galaxy in the Local Group, with its stellar disk 100,000 ly in diameter and, on average 1,000 ly thick. The Milky Way is 1.5 trillion times the mass of the Sun. To compare the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter, the Milky Way would be the size of the contiguous United States. There is a ring-like filament of stars rippling above and below the flat galactic plane, wrapping around the Milky Way at a diameter of 150,000–180,000 light-years, which may be part of the Milky Way itself. Estimates of the mass of the Milky Way vary, depending upon the method and data used; the low end of the estimate range is 5.8×1011 solar masses, somewhat less than that of the Andromeda Galaxy.
Measurements using the Very Long Baseline Array in 2009 found
NGC 508 occasionally referred to as PGC 5099 or UGC 939, is an elliptical galaxy in the constellation Pisces. It located 247 million light-years from the Solar System and was discovered on 12 September 1784 by British astronomer William Herschel. Herschel described the objects as "Two. Both eF, S, but unequal.". His observed position is accurate. John Louis Emil Dreyer, creator of the New General Catalogue, described the galaxy as "very faint, northern of two", with the other object being NGC 507; the Galaxy has an apparent size of 1.1 × 1.1 arcmins and a recessional velocity of 5525 kilometers per second. It is thought to be a group member with NGC 507, but as there is no evidence of interaction between the objects, the two are not a physical pair. Although NGC 508 is treated as part of Arp 229, the description of the Arp-galaxy only applies to the larger NGC 507; as of such, the term Arp 229 should only be used as an alternative designation NGC 507. Elliptical galaxy List of NGC objects Pisces NGC 508 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images SEDS
NGC 504 occasionally referred to as PGC 5084 or UGC 935, is a lenticular galaxy located 189 million light-years from the Solar System in the constellation Pisces. It was discovered on 22 November 1827 by astronomer John Herschel; the object was listed twice in the General Catalogue, precursor of the New General Catalogue, as both GC 291 and GC 292. Herschel discovered the object without recording a visual description. However, he noted the nebula "precedes NGC 507 by about 10 seconds and is half a field to the south of it. NGC 504 was also independently discovered by Heinrich d'Arrest, using an 11" reflecting telescope in Copenhagen and assuming the object was new; this led to Herschel cataloguing the two observations separately as GC 291 and GC 292. The objects were combined by John Louis Emil Dreyer with the creation of the New General Catalogue, in which the galaxy was described as "very faint, small". Lenticular galaxy List of NGC objects Pisces NGC 504 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images SEDS
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