Sirius A / B

The position of Sirius.
Observation data Epoch J2000.0 (ICRS)
Constellation (pronunciation)	Canis Major
Right ascension	06h 45m 08.9173s[1][2]
Declination	−16° 42′ 58.017″[1][2]
Apparent magnitude (V)	−1.47 (A)[1] / 8.30 (B)[3]
Characteristics
Spectral type	A1V (A)[1] / DA2 (B)[3]
U-B color index	−0.05 (A)[4] / −1.04 (B)[3]
B-V color index	0.01 (A)[1] / −0.03 (B)[3]
Astrometry
Radial velocity (Rv)	−7.6[1] km/s
Proper motion (μ)	RA: −546.05[1][2] mas/yr Dec.: −1223.14[1][2] mas/yr
Parallax (π)	379.21 ± 1.58[1] mas
Distance	8.6 ± 0.04 ly (2.64 ± 0.01 pc)
Absolute magnitude (MV)	1.42 (A)[5] / 11.18 (B)[3]
Visual binary orbit[6], p. 195
Companion	α CMa B
Period (P)	50.09 yr
Semimajor axis (a)	7.56"
Eccentricity (e)	0.592
Inclination (i)	136.5°
Longitude of the node (Ω)	44.6°
Periastron epoch (T)	1894.13
Argument of periastron (ω)	147.3°
Details
Mass	2.02[7] (A) / 0.978[7] (B) M☉
Radius	1.711[7] (A) / 0.0084 ± 3%[8] (B) R☉
Surface gravity (log g)	4.33[9] (A)/8.57[8] (B)
Luminosity	25.4[7] (A) / 0.026[10] (B) L☉
Temperature	9,940[9] (A) / 25,200[7] (B) K
Metallicity	[Fe/H] =0.50[11] (A)
Rotation	16 km/s[12] (A)
Age	2-3 × 108[7] years
Other designations
System: α Canis Majoris, α CMa, 9 Canis Majoris, 9 CMa, HD 48915, HR 2491, BD -16°1591, GCTP 1577.00 A/B, GJ 244 A/B, LHS 219, ADS 5423, LTT 2638, HIP 32349. B: EGGR 49, WD 0642-166.[1][13][14]

Sirius (α CMa / α Canis Majoris / Alpha Canis Majoris) (pronounced /ˈsɪɹiəs/^[15]) is the brightest star in the night sky with a visual apparent magnitude of −1.47, almost twice as bright as Canopus, the next brightest star. What appears as a single star to the naked eye is actually a binary star system, consisting of a white main sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. Sirius Satellite Radio NASDAQ: SIRI is one of two satellite radio (SDARS) services operating in the United States and Canada, along with XM Satellite Radio. ... Sirius may refer to several topics: // Astronomy Sirius (α Canis Majoris, also known as the Dog Star) is the brightest star (−1. ... Wikipedia does not have an article with this exact name. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... It has been suggested that this article or section be merged into Julian epoch. ... The J2000. ... This article is about the star grouping. ... From the dawn of time, poop observed the sky and grouped stars into patterns or constellations. ... Canis Major (pronounced , Latin: ) is one of the 88 modern constellations, and was also in Ptolemys list of 48 constellations. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (abbrev. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... This article or section does not adequately cite its references or sources. ... In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. ... In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. ... Illustration of the use of optical wavelength interferometry to determine precise positions of stars. ... Radial velocity is the velocity of an object in the direction of the line of sight. ... kilometre per second is an SI derived unit of both speed (scalar) and velocity (vector), signified by the symbol km/s or km s-1. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... For other uses, see Parallax (disambiguation). ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... Distance is a numerical description of how far apart objects are at any given moment in time. ... A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in vacuum in one year. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... In geometry, the semi-major axis (also semimajor axis) a applies to ellipses and hyperbolas. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... For the science fiction novella by William Shunn, see Inclination (novella). ... It has been suggested that this article or section be merged into Orbital node. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... The argument of periapsis (ω) is the orbital element describing the angle of an orbiting bodys periapsis (the point of closest approach to the central body), relative to its ascending node (the point where the body crosses the plane of reference from South to North). ... For other uses, see Mass (disambiguation). ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... This article is about an authentication, authorization, and accounting protocol. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... The surface gravity of a Killing horizon is the acceleration, as exerted at infinity, needed to keep an object at the horizon. ... This article does not cite any references or sources. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... For other uses, see Temperature (disambiguation). ... For other uses, see Kelvin (disambiguation). ... The globular cluster M80. ... This illustration shows the oblate appearance of the star Achernar caused by rapid rotation. ... This article is about the astronomical object. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A star catalogue, or star catalog, is an astronomical catalog that lists stars. ... The Henry Draper Catalogue is an astronomy catalogue with astrometric and spectroscopic data about more than 225,000 stars. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... The Hipparcos and Tycho Catalogues (Tycho-1) are the primary products of the European Space Agencys astrometric mission, Hipparcos. ... Alpha (uppercase Α, lowercase α) is the first letter of the Greek alphabet. ... Bright stars can be bright because they produce more light, because they are closer to us, or both. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... This article does not cite any references or sources. ... For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ... This article or section does not adequately cite its references or sources. ...

Sirius is bright due to both its intrinsic luminosity and its closeness to the Sun. At a distance of 2.6 parsecs (8.6 light-years), the Sirius system is one of our near neighbours. Sirius A is about twice as massive as the Sun and has an absolute visual magnitude of 1.42. It is 25 times more luminous than the Sun^[7] but has a significantly lower luminosity than other bright stars such as Canopus or Rigel. The system is between 200 and 300 million years old.^[7] It was originally composed of two bright bluish stars. The more massive of these, Sirius B, consumed its resources and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf around 120 million years ago.^[7] This article does not cite any references or sources. ... Sol redirects here. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... This list of the nearest stars to Earth is ordered by increasing distance out to a maximum of 5 parsecs (16. ... Rigel (pronounced ) (β Orionis) is the brightest star in the constellation Orion and the seventh brightest star in the sky, with visual magnitude 0. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... This article or section does not adequately cite its references or sources. ...

Sirius is also known colloquially as the "Dog Star", reflecting its prominence in its constellation, Canis Major (English: Big Dog).^[16] It is the subject of more mythological and folkloric tales than any other star apart from the sun. The heliacal rising of Sirius marked the flooding of the Nile in Ancient Egypt and the 'Dog Days' of summer for the Ancient Greeks, while to the Polynesians it marked winter and was an important star for navigation around the Pacific Ocean. This article is about the star grouping. ... Canis Major (pronounced , Latin: ) is one of the 88 modern constellations, and was also in Ptolemys list of 48 constellations. ... The English language is a West Germanic language that originates in England. ... The heliacal rising of a star (or other body such as the moon or a planet) occurs when it first becomes visible above the eastern horizon at dawn, after a period where it was hidden below the horizon or when it was just above the horizon but hidden by the... The pyramids are the most recognizable symbols of the civilization of ancient Egypt. ...

Observational history

Hieroglyph of Sirius/Sopdet Hieroglyphics redirects here. ...

Sirius is recorded in the earliest astronomical records, known in Ancient Egypt as Sopdet (Greek: Sothis). During the era of the Middle Kingdom, Egyptians based their calendar on the heliacal rising of Sirius, namely the day it becomes visible just before sunrise after moving far enough away from the glare of the sun. This occurred just before the annual flooding of the Nile and the summer solstice,^[17] after a 70 day absence from the skies.^[18] The hieroglyph for Sothis features a star and a triangle. Sothis was identified with the great goddess Isis who formed a part of a trinity with her husband Osiris and their son Horus, while the 70 day period symbolised the passing of Isis and Osiris though the duat (Egyptian underworld).^[18] For other uses, see Astronomy (disambiguation). ... The pyramids are the most recognizable symbols of the civilization of ancient Egypt. ... Sothis is the Greek name of a starn that the Egyptians considered unusually significant. ... The Middle Kingdom is the period in the history of ancient Egypt stretching from the establishment of the Eleventh Dynasty to the end of the Fourteenth Dynasty, roughly between 2030 BC and 1640 BC. The period comprises two phases, the 11th Dynasty, which ruled from Thebes and the 12th Dynasty... The ancient civil Egyptian Calendar, known as the Annus Vagus or Wandering Year, had a year that was 365 days long, consisting of 12 months of 30 days each, plus 5 extra days at the end of the year. ... The heliacal rising of a star (or other body such as the moon or a planet) occurs when it first becomes visible above the eastern horizon at dawn, after a period where it was hidden below the horizon or when it was just above the horizon but hidden by the... For other uses, see Nile (disambiguation). ... “Summer solstice” redirects here. ... This article discusses the ancient goddess Isis. ... For other uses, see Osiris (disambiguation). ... Ihy redirects here. ... In Egyptian mythology, Duat (also called Akert or Amenthes) is the underworld, where the sun traveled from west to east during the night and where dead souls were judged by Osiris, using a feather, representing Truth. ...

The Ancient Greeks believed that the appearance of Sirius heralded the hot and dry summer, and feared its effects on making plants wilt, men weaken and women become aroused.^[19] Due to its brightness, Sirius would have been noted to twinkle more in the unsettled weather conditions of early summer. To Greek observers, this signified certain emanations which caused its malign influence. People suffering its effects were said to be astroboletos/αστροβολητος or 'star-struck'. It was described as 'burning' or 'flaming' in literature.^[20] The season following the star's appearance came to be known as the Dog Days of summer.^[21] The inhabitants of the island of Ceos in the Aegean Sea would offer sacrifices to Sirius and Zeus to bring cooling breezes, and would await the reappearance of the star in summer. If it rose clear, it would portend good fortune; if it was misty or faint then it foretold (or emanated) pestilence. Coins retrieved from the island from the third century BC feature dogs or stars with emanating rays, highlighting Sirius' importance.^[22] The Romans celebrated the heliacal setting of Sirius around April 25, sacrificing a dog, along with incense, wine, and a sheep, to the goddess Robigo so that the star's emanations would not cause wheat rust on wheat crops that year.^[23] Dog Days or dog days of summer are typically the hottest and most humid times of the year. ... Kea, also known as Gia (Κέα / Τζια in Greek), Tzia and Keos (Ancient: Κέως), is an island of the Cyclades archipelago, in the Aegean sea, in Greece. ... Look up Aegean Sea in Wiktionary, the free dictionary. ... For other uses, see Zeus (disambiguation). ... is the 115th day of the year (116th in leap years) in the Gregorian calendar. ... In Roman mythology, Robigo was the female version of Robigus, the god who protected crops from disease. ... Families Pucciniaceae Melampsoraceae Coleosporiaceae Cronartiaceae Phragmidiaceae Pucciniastraceae Rusts are fungi of the order Uredinales. ...

Ptolemy of Alexandria mapped the stars in Book VII and VIII of his Almagest, in which he used Sirius as the location for the globe's central meridian. He curiously depicted it as one of six red-coloured stars (see the Red controversy section below). The other five are, in fact, class M and K stars, such as Arcturus and Betelgeuse.^[24][25] This article is about the geographer, mathematician and astronomer Ptolemy. ... Almagest is the Latin form of the Arabic name (al-kitabu-l-mijisti, i. ... This article is about the brightest star in the night sky of Earth. ... For other uses, see Arcturus (disambiguation). ... This article is about the star. ...

Bright stars were important to the ancient Polynesians for navigation between the many islands and atolls of the Pacific Ocean. Low on the horizon, they acted as stellar compasses to assist mariners in charting courses to particular destinations. They also served as latitude markers; the declination of Sirius matches the latitude of the island of Fiji at 17°S and thus passes directly over the island each night.^[26] Sirius served as the body of a 'Great Bird' constellation called Manu, with Canopus as the southern wingtip and Procyon the northern wingtip, which divided the Polynesian night sky into two hemispheres.^[27] Just as the appearance of Sirius in the morning sky marked summer in Greece, so it marked the chilly onset of winter for the Māori, whose name Takurua described both the star and the season. Its culmination at the winter solstice was marked by celebration in Hawaii, where it was known as Ka'ulua 'Queen of Heaven'. Many other Polynesian names have been recorded, including Tau-ua in the Marquesas Islands, Rehua in New Zealand, and Aa and Hoku-Kauopae in Hawaii.^[28] Polynesian culture refers to the aboriginal culture of the Polynesian-speaking peoples of Polynesia and the Polynesian outliers. ... This article is about the Māori people of New Zealand. ... This article is about the astronomical and cultural event of winters solstice, also known as midwinter. ... This article is about the U.S. State. ... National motto: Mau‘u‘u ha‘e iti Official languages French, Tahitian Political status Dependent territory, administrative division of French Polynesia Capital Tai o Hae Largest City Tai o Hae Area 1,274 km² ( 492 sq. ...

In 1676, Edmond Halley spent a year on the island of Saint Helena in the South Atlantic surveying the southern stars. Some 40 years later in 1718 he discovered the proper motion of the hitherto presumed "fixed" stars after comparing his astrometric measurements with those given in Ptolemy's Almagest. Arcturus and Sirius were two noted to have moved significantly, the latter having progressed 30 arc minutes (about the diameter of the moon) southwards in 1800 years.^[29] // Portrait of Edmond Halley painted around 1687 by Thomas Murray (Royal Society, London) Portrait of Edmond Halley Bust of Edmond Halley in the Museum of the Royal Greenwich Observatory Edmond Halley FRS (sometimes Edmund; IPA: ) (November 8, 1656 – January 14, 1742) was an English astronomer, geophysicist, mathematician, meteorologist, and physicist. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... Illustration of the use of optical wavelength interferometry to determine precise positions of stars. ... This article does not cite any references or sources. ... This article is about Earths moon. ...

Discovery of a companion

A simulated image of Sirius A and B from Celestia

In 1844, German astronomer Friedrich Bessel deduced from changes in the proper motion of Sirius that it had an unseen companion.^[30] Nearly two decades later, on January 31, 1862, American telescope-maker and astronomer Alvan Graham Clark first observed the faint companion, which is now called Sirius B, or affectionately "the Pup".^[31] The visible star is now sometimes known as Sirius A. Since 1894, some apparent orbital irregularities in the Sirius system have been observed, suggesting a third very small companion star, but this has never been definitely confirmed. The best fit to the data indicates a six-year orbit around Sirius A and a mass of only 0.06 solar masses. This star would be five to ten magnitudes fainter than the white dwarf Sirius B, which would account for the difficulty of observing it.^[32] More recent observations have failed to confirm the existence of a third member of the Sirius system, but still have not completely ruled out the possibility that one exists too close to Sirius to be seen. An apparent "third star" observed in the 1920s seems to have been a background object.^[33] For other uses, see Celestia (disambiguation). ... Friedrich Wilhelm Bessel (July 22, 1784 – March 17, 1846) was a German mathematician, astronomer, and systematizer of the Bessel functions (which, despite their name, were discovered by Daniel Bernoulli). ... is the 31st day of the year in the Gregorian calendar. ... This article is about 1862 . ... Alvan Graham Clark (July 10, 1832 – June 9, 1897), born in Fall River, Massachusetts, was an American astronomer and telescope-maker. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

In 1915, Walter Sydney Adams, using a 60-inch (1.5 meter) reflector at Mount Wilson Observatory, observed the spectrum of Sirius B and determined that it was a faint whitish star.^[34] This would lead astronomers to conclude that it was a white dwarf, the second to be discovered.^[35] The diameter of Sirius A was first measured by Robert Hanbury Brown and Richard Q. Twiss in 1959 at Jodrell Bank using their stellar intensity interferometer.^[36] In 2005, using the Hubble Space Telescope, astronomers determined that Sirius B has nearly the diameter of the Earth, 12,000 kilometers (7,500 miles), with a mass that is 98% of the Sun.^{[37][38][39][40]} Walter Sydney Adams (December 20, 1876 – May 11, 1956) was an American astronomer. ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... The metre, or meter (symbol: m) is the SI base unit of length. ... The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California. ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... This article or section does not adequately cite its references or sources. ... Robert Hanbury Brown AC (31 August 1916 – 16 January 2002) was a British astronomer and physicist born in Aruvankadu, India. ... Richard Q. Twiss (? – 20 May 2005) is famous for his work on the Hanbury-Brown and Twiss effect with Robert Hanbury Brown. ... The 76m Lovell Telescope at Jodrell Bank Observatory. ... An intensity interferometer is the name given to devices that use the Hanbury-Brown and Twiss effect. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... This article is about Earth as a planet. ... Sol redirects here. ...

Red controversy

In 150 AD, the astronomer Ptolemy described Sirius as reddish, along with five other stars, Betelgeuse, Antares, Aldebaran, Arcturus and Pollux, all of which are clearly of orange or red hue.^[41] The discrepancy was first noted by amateur astronomer Thomas Barker, squire of Lyndon Hall in Rutland, who prepared a paper and spoke at a meeting of the Royal Society in London in 1760. The existence of other stars changing in brightness gave credence to the idea that some may change in colour too; Sir John Herschel noted this in 1839, possibly influenced by witnessing Eta Carinae two years earlier.^[42] Thomas Jefferson Jackson See resurrected discussion on red Sirius in 1892 with the publication of several papers in 1892, and a final summary in 1926.^[43] He cited not only Ptolemy but also the poet Aratus, the orator Cicero, and general Germanicus as colouring the star red, though acknowledging that none of the latter three authors were astronomers, the last two merely translating Aratus' poem Phaenomena.^[44] Seneca, too, had described Sirius as being of a deeper red colour than Mars.^[45] However, not all ancient observers saw Sirius as red. The 1st century AD poet Marcus Manilius described it as "sea-blue", as did the 4th century Avienus.^[46] It is the standard star for the color white in ancient China, and multiple records from the 2nd century BC up to the 7th century AD all describe Sirius as white in hue.^[47][48] This article is about the star. ... This article or section does not cite its references or sources. ... Aldebaran from the Arabic (الدبران al-dabarān) meaning the follower, (α Tau / α Tauri / Alpha Tauri) is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky. ... For other uses, see Arcturus (disambiguation). ... Pollux (β Gem / β Geminorum / Beta Geminorum) is one of the brightest star in the constellation Gemini and one of the brightest stars in the nighttime sky. ... Oakham Castle Rutland is traditionally Englands smallest county and is bounded on the west and north by Leicestershire, northeast by Lincolnshire, and southeast by Northamptonshire. ... Eta Carinae (η Carinae or η Car) is a highly luminous hypergiant double star. ... Thomas Jefferson Jackson (T. J. J.) See, (1866 to July 4, 1962). ... Aratus (Greek Aratos) (ca. ... For other uses, see Cicero (disambiguation). ... Germanicus Julius Caesar Claudianus (24 May 15 BC–October 10, 19) was a member of the Julio-Claudian dynasty of the early Roman Empire. ... Bust, traditionally thought to be Seneca, now identified by some as Hesiod. ... Marcus Manilius (fl. ... Avienus was a Latin writer of the 4th century. ...

In 1985, German astronomers Wolfhard Schlosser and Werner Bergmann published an account of an 8th century Lombardic manuscript, which contains De cursu stellarum ratio by St. Gregory of Tours. The Latin text taught readers how to determine the times of nighttime prayers from positions of the stars, and Sirius is described within as rubeola 'reddish'. The authors proposed this was further evidence Sirius B had been a red giant at the time.^[49] However, other astronomers replied that it was likely St. Gregory had been referring to Arcturus instead.^[50][51] For the village of the same name in Ontario, Canada, see Lombardy, Ontario. ... Saint Gregory of Tours (c. ... For other uses, see Latins and Latin (disambiguation). ...

The possibility that stellar evolution of either Sirius A or Sirius B could be responsible for this discrepancy has been rejected by astronomers on the grounds that the timescale of thousands of years is too short and that there is no sign of the nebulosity in the system that would be expected had such a change taken place.^[52] The interaction by third star, to date undiscovered, has also been proposed as a possibility for a red appearance.^[53] Alternative explanations are either that the description as red is a poetic metaphor for ill fortune, or that the dramatic scintillations of the star when it was observed rising left the viewer with the impression that it was red. To the naked eye, it often appears to be flashing with red, white and blue hues when near the horizon.^[52]

Visibility

The image of Sirius A and Sirius B taken by Hubble Space Telescope. The white dwarf can be seen to the lower left.^[54] The crosshairs and concentric rings are instrumental effects.

With an apparent magnitude of −1.47, Sirius is the brightest star in the night sky, almost twice the brightness of the second brightest star, Canopus.^[55] However, it is not as bright as the Moon, Venus, or Jupiter. Mercury and Mars are also brighter than Sirius at times.^[56][57] Sirius can be seen from almost every inhabited region of the Earth's surface, with only those living north of 73 degrees unable to see it. However, it does not rise very high when viewed from some northern cities, reaching only 13° above the horizon from Saint Petersburg.^[58] Sirius, along with Procyon and Betelgeuse, forms one of the three vertices of the Winter Triangle to observers in the Northern Hemisphere.^[59] Sirius can even be observed in daylight with the naked eye under the right conditions. Ideally, the sky should be very clear, with the observer at a high altitude, the star passing overhead, and the sun low down on the horizon.^[60] Image File history File linksMetadata Sirius_A_and_B_Hubble_photo. ... Image File history File linksMetadata Sirius_A_and_B_Hubble_photo. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... This article or section does not adequately cite its references or sources. ... Image formation in a confocal microscope: central longitudinal (XZ) slice. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... This article does not cite any references or sources. ... This article is about Earths moon. ... For other uses, see Venus (disambiguation). ... For other uses, see Jupiter (disambiguation). ... This article is about the planet. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... This article is about Earth as a planet. ... Some of the northernmost settlements in the world are: Alert, Ellesmere Island, Nunavut, Canada 82°28 N — Pop. ... Saint Petersburg (Russian: Санкт-Петербу́рг, English transliteration: Sankt-Peterburg), colloquially known as Питер (transliterated Piter), formerly known as Leningrad (Ленингра́д, 1924–1991) and Petrograd (Петрогра́д, 1914–1924), is a city located in Northwestern Russia on the delta of the river Neva at the east end of the Gulf of Finland... Procyon (α CMi / α Canis Minoris / Alpha Canis Minoris) is the brightest star in the constellation Canis Minor and the eighth brightest star in the nighttime sky. ... This article is about the star. ... In geometry, a vertex (plural vertices) is a special kind of point, usually a corner of a polygon, polyhedron, or higher dimensional polytope. ... The Winter Triangle is an astronomical asterism involving an imaginary triangle drawn, during the winter, upon the northern hemispheres celestial sphere; with its defining vertices at Betelgeuse, Procyon, and Sirius. ... Northern hemisphere highlighted in yellow. ...

The orbital motion of the Sirius binary system brings the two stars to a minimum angular separation of 3″ and a maximum of 11″. At the closest approach, it is an observational challenge to distinguish the white dwarf from its more luminous companion, requiring a telescope with at least 300 mm (12 in) aperture and excellent seeing conditions. A periastron occurred in 1994^[61] and the pair have since been moving apart, making them easier to split with a telescope.^[62] A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7. ... This article does not cite any references or sources. ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...

At a distance of 2.6 parsecs or 8.6 light-years, the Sirius system contains two of the eight nearest stars to the Solar System^[63] and is the fifth closest stellar system to ours.^[63] This proximity is the main reason for its brightness, as with other near stars such as Alpha Centauri and in stark contrast to distant, highly luminous supergiants such as Canopus, Rigel or Betelgeuse.^[64] However, it is still around 25 times more luminous than the Sun.^[7] The closest large neighbouring star to Sirius is Procyon, 1.61 parsecs or 5.24 light years away.^[65] The Voyager 2 spacecraft, launched in 1977 to study the four Jovian planets in the Solar System, is expected to pass within 4.3 light years of Sirius in approximately 296,000 years.^[66] A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... This list of the nearest stars to Earth is ordered by increasing distance out to a maximum of 5 parsecs (16. ... This article is about the Solar System. ... Alpha Centauri (α Cen / α Centauri, also known as Rigil Kentaurus), is the brightest star system in the southern constellation of Centaurus. ... This article does not cite any references or sources. ... Rigel (pronounced ) (β Orionis) is the brightest star in the constellation Orion and the seventh brightest star in the sky, with visual magnitude 0. ... This article is about the star. ... Procyon (α CMi / α Canis Minoris / Alpha Canis Minoris) is the brightest star in the constellation Canis Minor and the eighth brightest star in the nighttime sky. ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... From top: Neptune, Uranus, Saturn, and Jupiter. ... This article is about the Solar System. ...

System

Sirius is a binary star system consisting of two white stars orbiting each other with a separation of about 20 astronomical units^[67] (roughly the distance between the Sun and Uranus) and a period of just over 50 years. The brighter component, termed Sirius A, is a main sequence star of spectral type A1V, with an estimated surface temperature of 9,940 K.^[9] Its companion, Sirius B, is a star that has already evolved off the main sequence and become a white dwarf. Currently 10,000 times less luminous in the visual spectrum, Sirius B was once the more massive of the two.^[68] The age of the system has been estimated at around 230 million years. Early in its lifespan it was thought to have been two bluish white stars orbiting each other in an elliptical orbit every 9.1 years.^[68] The system emits a higher than expected level of infrared radiation, as measured by IRAS space-based observatory. This may be an indication of dust in the system, and is considered somewhat unusual for a binary star.^[69][65] The astronomical unit (AU or au or a. ... Sol redirects here. ... For other uses, see Uranus (disambiguation). ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ... For other uses, see Kelvin (disambiguation). ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... This article or section does not adequately cite its references or sources. ... For other uses, see Infrared (disambiguation). ... The Infrared Astronomical Satellite (IRAS) was a space-based observatory that performed a survey of the entire sky at infrared wavelengths. ...

Sirius A

An artist's impression of Sirius A and Sirius B. Sirius A is the larger of the two stars.

Sirius A has a mass of around 2.1 times that of the Sun.^[70][65] The radius of this star has been measured by an astronomical interferometer, giving an estimated angular diameter of 5.936±0.016 mas. The projected rotational velocity is a relatively low 16 km/s, which does not produce any significant flattening of its disk.^[12] This is at marked variance with the similar-sized Vega, which rotates at a much faster 274 km/s and bulges prominently around its equator.^[71] Image File history File linksMetadata Download high resolution version (4000x3000, 2379 KB) Summary An Artists Impression of Sirius A and Sirius B Source: http://hubblesite. ... Image File history File linksMetadata Download high resolution version (4000x3000, 2379 KB) Summary An Artists Impression of Sirius A and Sirius B Source: http://hubblesite. ... Sol redirects here. ... Diagram showing a possible layout for an astronomical interferometer, with the mirrors laid out in a parabolic arrangement (similar to the shape of a conventional telescope mirror). ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... This illustration shows the oblate appearance of the star Achernar caused by rapid rotation. ... For other uses, see Vega (disambiguation). ...

Stellar models suggest that the star formed during the collapsing of a molecular cloud, and that after 10 million years, its internal energy generation was derived entirely from nuclear reactions. The core became convective and utilized the CNO cycle for energy generation.^[12] It is predicted that Sirius A will have completely exhausted the store of hydrogen at its core within a billion (10⁹) years of its formation. At this point it will pass through a red giant stage, then settle down to become a white dwarf. A molecular cloud is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen (H2). ... The convection zone is a region of a stars interior where energy is transferred toward the surface by convection currents, rather than energetic photons. ... This article does not cite its references or sources. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ...

The spectrum of Sirius A shows deep metallic lines, indicating an enhancement in elements heavier than helium, such as iron.^[12][65] When compared to the Sun, the proportion of iron in the atmosphere of Sirius A relative to hydrogen is given by ,^[11] which is equivalent to 10^0.5, meaning it has 316% of the proportion of iron in the Sun's atmosphere. The high surface content of metallic elements is unlikely to be true of the entire star. Instead these may be suspended by a thin convection zone at the surface.^[12] The convection zone is a region of a stars interior where energy is transferred toward the surface by convection currents, rather than energetic photons. ...

Sirius B

With a mass nearly equal to the Sun's, Sirius B is one of the more massive white dwarfs known; it is almost double the 0.5–0.6 solar mass average. Yet that same mass is packed into a volume roughly equal to the Earth. The current surface temperature is 25,200 K.^[7] However, since there is no internal source of energy generation, Sirius B will steadily cool as the remaining heat is radiated into space over a period of more than two billion years.^[72] In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... This article is about Earth as a planet. ...

A white dwarf forms only after the star has evolved from the main sequence and then passed through a red giant stage. This occurred when Sirius B was less than half its current age, approximately 120 million years ago. The original star had an estimated 5 solar masses^[73] and was a B-type star (roughly B4-5)^[74][75] when it still was on the main sequence. While it passed through the red giant stage, Sirius B may have enriched the metallicity of its companion. The globular cluster M80. ...

This star is primarily composed of a carbon-oxygen mixture that was generated by helium fusion in the progenitor star.^[7] This is overlaid by an envelope of lighter elements, with the materials segregated by mass because of the high surface gravity.^[76] Hence the outer atmosphere of Sirius B is now almost pure hydrogen—the element with the lowest mass—and no other elements are seen in this star's spectrum.^[77]

Sirius supercluster

In 1909, Ejnar Hertzsprung was the first to suggest that Sirius was a member of the Ursa Major Moving Group, based on his observations of the system's movements across the sky. The Ursa Major Group is a set of 220 stars that share a common motion through space and were once formed as members of an open cluster, which has since become gravitationally unbound.^[78] However, analyses in 2003 and 2005 found Sirius's membership in the group to be questionable; the Ursa Major Group has an estimated age of 500±100 million years, while Sirius, with metallicity similar to the Sun's, has an age that is only half this, making it too young to belong to the group.^[7][79][80] Sirius may instead be a member of the proposed Sirius Supercluster, along with other scattered stars such as Beta Aurigae, Alpha Coronae Borealis, Beta Crateris, Beta Eridani and Beta Serpentis.^[81] This is one of three large clusters located within 500 light years of the Sun. The other two are the Hyades and the Pleiades, and each of these clusters consists of hundreds of stars.^[82] Ejnar Hertzsprung (October 8, 1873, Copenhagen – October 21, 1967, Roskilde) was a Danish chemist and astronomer. ... The Ursa Major Moving Group, also known as Collinder 285, is the closest moving group to Earth, that is, a set of stars with common velocities in space, thought to have a common origin. ... Galactic cluster redirects here. ... The globular cluster M80. ... Sol redirects here. ... Beta Aurigae (β Aur / β Aurigae) is the second brightest star in the constellation Auriga. ... Alpha Coronae Borealis (α CrB / α Coronae Borealis) is a binary star in the constellation Corona Borealis. ... Cursa (foot bank [ of the Orion ]) is the name of the beta Eridani. ... Beta Serpentis (β Ser / β Serpentis) is a star system in the constellation Serpens. ... The Hyades (ÆΥάδες also known as Melotte 25 or Collinder 50 or Caldwell 41) is an open star cluster located in the constellation Taurus. ... A shorter exposure shows less nebulosity. ...

Etymology and cultural significance

The most commonly used proper name of this star comes from the Latin Sīrius, from Greek Σείριος (Seirios, "glowing" or "scorcher"),^[83] although the word is possibly not of Greek origin. The name's earliest recorded use dates from the 7th century BC in Hesiod's poetic work Works and Days.^[84] Sirius has over 50 other designations and names attached to it.^[55] In Arabic it is known as الشعرى (transliteration: al-ši‘rā or al-shira; English: "the leader"),^[85] from which the alternate name Aschere derives. In Sanskrit, it is known as Mrgavyadha "deer hunter" or Lubdhaka "hunter". As Mrgavyadha, the star represents Rudra (Shiva)^[86][87]. In Scandinavia, the star has been known as Lokabrenna ("burning done by Loki", or "Loki's torch"), while the Japanese vernacular name of the star is 青星 (Aoboshi, "blue star"). In the astrology of the Middle Ages, Sirius was a Behenian fixed star,^[88] associated with beryl and juniper. Its kabbalistic symbol was listed by Heinrich Cornelius Agrippa.^[89] For other uses, see Latins and Latin (disambiguation). ... Roman bronze bust, the so-called Pseudo-Seneca, now identified by some as possibly Hesiod Hesiod (Hesiodos, ) was an early Greek poet and rhapsode, who presumably lived around 700 BC. Hesiod and Homer, with whom Hesiod is often paired, have been considered the earliest Greek poets whose work has survived... The book Works and Days Works and Days (in ancient Greek , which sometimes goes by the Latin name Opera et Dies, as in the OCT) is a Greek poem of some 800 verses written by Hesiod (around 700 BC). ... Arabic redirects here. ... The English language is a West Germanic language that originates in England. ... Sanskrit ( , for short ) is a classical language of India, a liturgical language of Hinduism, Buddhism, Sikhism, and Jainism, and one of the 23 official languages of India. ... Rudra (Sanskrit: रुद्रः) (Howler) is a Rigvedic God of the storm, the hunt, death, Nature and the Wind. ... For other uses, see Shiva (disambiguation). ... Hand-coloured version of the anonymous Flammarion woodcut (1888). ... The Middle Ages formed the middle period in a traditional schematic division of European history into three ages: the classical civilization of Antiquity, the Middle Ages, and modern times, beginning with the Renaissance. ... The Behenian fixed stars are a selection of fifteen stars considered especially useful for magical applications in the medieval astrology of Europe and the Arab world. ... Three varieties of beryl: Morganite, Aquamarine, and Heliodor The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al2(SiO3)6. ... Species Junipers are coniferous plants in the genus Juniperus of the cypress family Cupressaceae. ... The tree of life Kabbalah (קבלה Reception, Standard Hebrew Qabbala, Tiberian Hebrew Qabbālāh; also written variously as Cabala, Cabalah, Cabbala, Cabbalah, Kabala, Kabalah, Kabbala, Qabala, Qabalah) is a religious philosophical system claiming an insight into divine nature. ... Image File history File links after Agrippa File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Cornelius Agrippa, as portrayed in Libri tres de occulta philosophia. ...

Many cultures have historically attached special significance to Sirius, particularly in relation to dogs. Indeed, it is often colloquially called the "Dog Star" as the brightest star of Canis Major, the "Great Dog" constellation. It was also classically depicted as Orion's dog. The Ancient Greeks also thought that Sirius' emanations could affect dogs adversely, making them behave abnormally in the heat of summer ("Dog Days"). Their excessive panting was thought to place them at risk of desiccation and disease. In extreme cases, a foaming dog may have rabies, which could infect and kill humans who'd been bitten.^[22] The Romans knew these days as dies caniculares and the star as Canicula ("little dog"). In Chinese astronomy the star is known as the star of the 'celestial wolf' (Chinese and Japanese: 天狼; Korean: 천랑;