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Sirius

Sirius is the brightest star in the night sky. Its name is derived from the Greek word Σείριος, or Seirios, meaning lit. 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated Alpha CMa or α CMa. With a visual apparent magnitude of −1.46, Sirius is almost twice as bright as Canopus, the next brightest star. Sirius is a binary star consisting of a main-sequence star of spectral type A0 or A1, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.[25]

Sirius
Location of Sirius (circled)
Observation data
Epoch J2000.0      Equinox ICRS
Constellation Canis Major
Pronunciation /ˈsɪriəs/[1]
Sirius A
Right ascension 06h 45m 08.917s[2]
Declination −16° 42′ 58.02″[2]
Apparent magnitude (V) −1.46[3]
Sirius B
Right ascension 06h 45m 09.0s[4]
Declination −16° 43′ 06″[4]
Apparent magnitude (V) 8.44[5]
Characteristics
Sirius A
Evolutionary stage Main sequence
Spectral type A0mA1 Va[6]
U−B colour index −0.05[3]
B−V colour index +0.00[3]
Sirius B
Evolutionary stage White dwarf
Spectral type DA2[5]
U−B colour index −1.04[7]
B−V colour index −0.03[7]
Astrometry
Radial velocity (Rv)−5.50[8] km/s
Sirius A
Proper motion (μ) RA: −546.01 mas/yr[9]
Dec.: −1,223.07 mas/yr[9]
Parallax (π)379.21 ± 1.58 mas[9]
Distance8.60 ± 0.04 ly
(2.64 ± 0.01 pc)
Absolute magnitude (MV)+1.43[10]
Sirius B
Proper motion (μ) RA: −461.571 mas/yr[11]
Dec.: −914.520 mas/yr[11]
Parallax (π)374.4896 ± 0.2313 mas[11]
Distance8.709 ± 0.005 ly
(2.670 ± 0.002 pc)
Absolute magnitude (MV)+11.18[7]
Orbit[12]
Primaryα Canis Majoris A
Companionα Canis Majoris B
Period (P)50.1284 ± 0.0043 yr
Semi-major axis (a)7.4957 ± 0.0025″
Eccentricity (e)0.59142 ± 0.00037
Inclination (i)136.336 ± 0.040°
Longitude of the node (Ω)45.400 ± 0.071°
Periastron epoch (T)1,994.5715 ± 0.0058
Argument of periastron (ω)
(secondary)
149.161 ± 0.075°
Details
Sirius A
Mass2.063±0.023[12] M
Radius1.711[13] R
Luminosity25.4[13] L
Surface gravity (log g)4.33[14] cgs
Temperature9,940[14] K
Metallicity [Fe/H]0.50[15] dex
Rotational velocity (v sin i)16[16] km/s
Age242±5[12] Myr
Sirius B
Mass1.018 ± 0.011[12] M
Radius0.0084 ± 3%[17] R
Luminosity0.056[18] L
Surface gravity (log g)8.57[17] cgs
Temperature25,000 ± 200[13] K
Age228+10
−8
[12] Myr
Other designations
Dog Star, Aschere, Canicula, Al Shira, Sothis,[19] Alhabor,[20] Mrgavyadha, Lubdhaka,[21] Tenrōsei,[22] α Canis Majoris (α CMa), 9 Canis Majoris (9 CMa), HD 48915, HR 2491, BD−16°1591, GJ 244, LHS 219, ADS 5423, LTT 2638, HIP 32349[23]
Sirius B: EGGR 49, WD 0642-166, GCTP 1577.00[24]
Database references
A
B

Sirius appears bright because of its intrinsic luminosity and its proximity to the Solar System. At a distance of 2.64 parsecs (8.6 ly), the Sirius system is one of Earth's nearest neighbours. Sirius is gradually moving closer to the Solar System, so it is expected to increase in brightness slightly over the next 60,000 years, reaching a peak magnitude of −1.68. After that time, its distance will begin to increase, and it will become fainter, but it will continue to be the brightest star in the Earth's night sky for approximately the next 210,000 years, before Vega, another A-type star and more luminous than Sirius, becomes the brightest star.[26]

Sirius A is about twice as massive as the Sun (M) and has an absolute visual magnitude of +1.43. It is 25 times as luminous as the Sun,[13] but has a significantly lower luminosity than other bright stars such as Canopus, Betelgeuse, or Rigel. The system is between 200 and 300 million years old.[13] It was originally composed of two bright bluish stars. The initially more massive of these, Sirius B, consumed its hydrogen fuel 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.[13]

Sirius is colloquially known as the "Dog Star", reflecting its prominence in its constellation, Canis Major (the Greater Dog).[19] 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, mostly in the Southern Hemisphere, the star marked winter and was an important reference for their navigation around the Pacific Ocean.

Observational history

The brightest star seen from Earth, Sirius is recorded in some of the earliest astronomical records. Its displacement from the ecliptic causes its heliacal rising to be remarkably regular compared to other stars, with a period of almost exactly 365.25 days holding it constant relative to the solar year. This rising occurs at Cairo on 19 July (Julian), placing it just before the onset of the annual flooding of the Nile during antiquity.[27] Owing to the flood's own irregularity, the extreme precision of the star's return made it important to the ancient Egyptians,[27] who worshipped it as the goddess Sopdet (Ancient Egyptian: Spdt, "Triangle";[a] Greek: Σῶθις, Sō̂this), guarantor of the fertility of their land.[b]

The ancient Greeks observed that the appearance of Sirius as the morning star heralded the hot and dry summer and feared that the star caused plants to wilt, men to weaken, and women to become aroused.[29] Owing to its brightness, Sirius would have been seen to twinkle more in the unsettled weather conditions of early summer. To Greek observers, this signified emanations that caused its malignant influence. Anyone suffering its effects was said to be "star-struck" (ἀστροβόλητος, astrobólētos). It was described as "burning" or "flaming" in literature.[30] The season following the star's reappearance came to be known as the "dog days".[31] 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 3rd century BC feature dogs or stars with emanating rays, highlighting Sirius's importance.[30]

The Romans celebrated the heliacal setting of Sirius around 25 April, 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.[32]

Bright stars were important to the ancient Polynesians for navigation of the Pacific Ocean. They also served as latitude markers; the declination of Sirius matches the latitude of the archipelago of Fiji at 17°S and thus passes directly over the islands each sidereal day.[33] 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.[34] Just as the appearance of Sirius in the morning sky marked summer in Greece, it marked the 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 Ta'urua-fau-papa "Festivity of original high chiefs" and Ta'urua-e-hiti-i-te-tara-te-feiai "Festivity who rises with prayers and religious ceremonies" in Tahiti.[35]

Kinematics

In 1717, Edmond Halley discovered the proper motion of the hitherto presumed fixed stars[36] after comparing contemporary astrometric measurements with those from the second century AD given in Ptolemy's Almagest. The bright stars Aldebaran, Arcturus and Sirius were noted to have moved significantly; Sirius had progressed about 30 arcminutes (about the diameter of the Moon) to the southwest.[37]

In 1868, Sirius became the first star to have its velocity measured, the beginning of the study of celestial radial velocities. Sir William Huggins examined the spectrum of the star and observed a red shift. He concluded that Sirius was receding from the Solar System at about 40 km/s.[38][39] Compared to the modern value of −5.5 km/s, this was an overestimate and had the wrong sign; the minus sign (−) means that it is approaching the Sun.[40]

Distance

In his 1698 book, Cosmotheoros, Christiaan Huygens estimated the distance to Sirius at 27,664 times the distance from the Earth to the Sun (about 0.437 light-year, translating to a parallax of roughly 7.5 arcseconds).[41] There were several unsuccessful attempts to measure the parallax of Sirius: by Jacques Cassini (6 seconds); by some astronomers (including Nevil Maskelyne)[42] using Lacaille's observations made at the Cape of Good Hope (4 seconds); by Piazzi (the same amount); using Lacaille's observations made at Paris, more numerous and certain than those made at the Cape (no sensible parallax); by Bessel (no sensible parallax).[43]

Scottish astronomer Thomas Henderson used his observations made in 1832–1833 and South African astronomer Thomas Maclear's observations made in 1836–1837, to determine that the value of the parallax was 0.23 arcsecond, and error of the parallax was estimated not to exceed a quarter of a second, or as Henderson wrote in 1839, "On the whole we may conclude that the parallax of Sirius is not greater than half a second in space; and that it is probably much less."[44] Astronomers adopted a value of 0.25 arcsecond for much of the 19th century.[45] It is now known to have a parallax of nearly 0.4 arcseconds.

The Hipparcos parallax for Sirius is only accurate to about ±0.04 light years, giving a distance of 8.6 light years.[9] Sirius B is generally assumed to be at the same distance. Sirius B has a Gaia Data Release 3 parallax with a much smaller statistical margin of error, giving a distance of 8.709±0.005 light years, but it is flagged as having a very large value for astrometric excess noise, which indicates that the parallax value may be unreliable.[11]

Discovery of Sirius B

 
Hubble Space Telescope image of Sirius A and Sirius B. The white dwarf can be seen to the lower left. The diffraction spikes and concentric rings are instrumental effects.

In a letter dated 10 August 1844, the German astronomer Friedrich Wilhelm Bessel deduced from changes in the proper motion of Sirius that it had an unseen companion.[46] On 31 January 1862, American telescope-maker and astronomer Alvan Graham Clark first observed the faint companion, which is now called Sirius B, or affectionately "the Pup".[47] This happened during testing of an 18.5-inch (470 mm) aperture great refractor telescope for Dearborn Observatory, which was one of the largest refracting telescope lenses in existence at the time, and the largest telescope in the United States.[48] Sirius B's sighting was confirmed on 8 March with smaller telescopes.[49]

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 confirmed. The best fit to the data indicates a six-year orbit around Sirius A and a mass of 0.06 M. This star would be five to ten magnitudes fainter than the white dwarf Sirius B, which would make it difficult to observe.[50] Observations published in 2008 were unable to detect either a third star or a planet. An apparent "third star" observed in the 1920s is now believed to be a background object.[51]

In 1915, Walter Sydney Adams, using a 60-inch (1.5 m) reflector at Mount Wilson Observatory, observed the spectrum of Sirius B and determined that it was a faint whitish star.[52] This led astronomers to conclude that it was a white dwarf—the second to be discovered.[53] 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.[54] In 2005, using the Hubble Space Telescope, astronomers determined that Sirius B has nearly the diameter of the Earth, 12,000 kilometres (7,500 mi), with a mass 102% of the Sun's.[55]

Colour controversy

Twinkling of Sirius (apparent magnitude = −1.5) in the evening shortly before upper culmination on the southern meridian at a height of 20 degrees above the horizon. During 29 seconds Sirius moves on an arc of 7.5 minutes from the left to the right.

Around the year 150 AD,[56] the Greek astronomer of the Roman period, Ptolemy of Alexandria mapped the stars in Books VII and VIII of his Almagest, in which he used Sirius as the location for the globe's central meridian.[57] He described Sirius as reddish, along with five other stars, Betelgeuse, Antares, Aldebaran, Arcturus and Pollux, all of which are of orange or red hue.[56] 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.[58] The existence of other stars changing in brightness gave credibility 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.[59] Thomas Jefferson Jackson See resurrected discussion on red Sirius with the publication of several papers in 1892, and a final summary in 1926.[60] He cited not only Ptolemy but also the poet Aratus, the orator Cicero, and general Germanicus as calling the star red, though acknowledging that none of the latter three authors were astronomers, the last two merely translating Aratus's poem Phaenomena.[61] Seneca had described Sirius as being of a deeper red than Mars.[62] Not all ancient observers saw Sirius as red. The 1st-century poet Marcus Manilius described it as "sea-blue", as did the 4th-century Avienius.[63] It was the standard white star in ancient China, and multiple records from the 2nd century BC up to the 7th century AD all describe Sirius as white.[64][65]

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 a bright star described as rubeola—"reddish" was claimed to be Sirius. The authors proposed this was further evidence Sirius B had been a red giant at the time.[66] Other scholars replied that it was likely St. Gregory had been referring to Arcturus.[67][68]

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 much too short and that there is no sign of the nebulosity in the system that would be expected had such a change taken place.[62] An interaction with a third star, to date undiscovered, has also been proposed as a possibility for a red appearance.[69] 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 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.[62]

Observation

 
Sirius (bottom) and the constellation Orion (right). The three brightest stars in this image—Sirius, Betelgeuse (top right) and Procyon (top left)—form the Winter Triangle. The bright star at top center is Alhena, which forms a cross-shaped asterism with the Winter Triangle.

With an apparent magnitude of −1.46, Sirius is the brightest star in the night sky, almost twice as bright as the second-brightest star, Canopus.[70] From Earth, Sirius always appears dimmer than Jupiter and Venus, as well as Mercury and Mars at certain times.[71] Sirius is visible from almost everywhere on Earth, except latitudes north of 73° N, and it does not rise very high when viewed from some northern cities (reaching only 13° above the horizon from Saint Petersburg).[72] Because of its declination of roughly −17°, Sirius is a circumpolar star from latitudes south of 73° S. From the Southern Hemisphere in early July, Sirius can be seen in both the evening where it sets after the Sun and in the morning where it rises before the Sun.[73] Along with Procyon and Betelgeuse, Sirius forms one of the three vertices of the Winter Triangle to observers in the Northern Hemisphere.[74]

Sirius can 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 on the horizon. These observing conditions are more easily met in the Southern Hemisphere, owing to the southerly declination of Sirius.[75]

The orbital motion of the Sirius binary system brings the two stars to a minimum angular separation of 3 arcseconds and a maximum of 11 arcseconds. 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. After a periastron occurred in 1994,[c] the pair moved apart, making them easier to separate with a telescope.[76] Apoastron occurred in 2019,[d] but from the Earth's vantage point, the greatest observational separation will occur in 2023, with an angular separation of 11.333".[77]

At a distance of 2.6 parsecs (8.6 ly), the Sirius system contains two of the eight nearest stars to the Sun, and it is the fifth closest stellar system to the Sun.[78] This proximity is the main reason for its brightness, as with other near stars such as Alpha Centauri, Procyon and Vega and in contrast to distant, highly luminous supergiants such as Canopus, Rigel or Betelgeuse.(Note that Canopus may be a bright giant)[79] It is still around 25 times more luminous than the Sun.[13] The closest large neighbouring star to Sirius is Procyon, 1.61 parsecs (5.24 ly) away.[80] The Voyager 2 spacecraft, launched in 1977 to study the four giant planets in the Solar System, is expected to pass within 4.3 light-years (1.3 pc) of Sirius in approximately 296,000 years.[81]

Stellar system

 
The orbit of Sirius B around A as seen from Earth (slanted ellipse). The wide horizontal ellipse shows the true shape of the orbit (with an arbitrary orientation) as it would appear if viewed straight on.
 
A Chandra X-ray Observatory image of the Sirius star system, where the spike-like pattern is due to the support structure for the transmission grating. The bright source is Sirius B. Credit: NASA/SAO/CXC

Sirius is a binary star system consisting of two white stars orbiting each other with a separation of about 20 AU[e] (roughly the distance between the Sun and Uranus) and a period of 50.1 years. The brighter component, termed Sirius A, is a main-sequence star of spectral type early A, with an estimated surface temperature of 9,940 K.[14] 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.[82] The age of the system has been estimated at around 230 million years. Early in its life, it is thought to have been two bluish-white stars orbiting each other in an elliptical orbit every 9.1 years.[82] The system emits a higher than expected level of infrared radiation, as measured by IRAS space-based observatory. This might be an indication of dust in the system, which is considered somewhat unusual for a binary star.[80][83] The Chandra X-ray Observatory image shows Sirius B outshining its partner as an X-ray source.[84]

In 2015, Vigan and colleagues used the VLT Survey Telescope to search for evidence of substellar companions, and were able to rule out the presence of giant planets 11 times more massive than Jupiter at 0.5 AU distance from Sirius A, 6–7 times the mass of Jupiter at 1–2 AU distance, and down to around 4 times the mass of Jupiter at 10 AU distance.[85] Similarly, Lucas and colleagues did not detect any companions around Sirius B.[86]

Sirius A

 
Comparison of Sirius A and the Sun, to scale and relative surface brightness

Sirius A has a mass of 2.063 M.[12][13][87] 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,[16] which does not produce any significant flattening of its disk.[88] 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.[89] A weak magnetic field has been detected on the surface of Sirius A.[90]

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 used the CNO cycle for energy generation.[88] It is calculated that Sirius A will have completely exhausted the store of hydrogen at its core within a billion (109) years of its formation, and will then evolve away from the main sequence.[91] It will pass through a red giant stage and eventually become a white dwarf.[92]

Sirius A is classed as an Am star because the spectrum shows deep metallic absorption lines,[93] indicating an enhancement of its surface layers in elements heavier than helium, such as iron.[80][88] The spectral type has been reported as A0mA1 Va, which indicates that it would be classified as A1 from hydrogen and helium lines, but A0 from the metallic lines that cause it to be grouped with the Am stars.[6] When compared to the Sun, the proportion of iron in the atmosphere of Sirius A relative to hydrogen is given by  ,[15] meaning iron is 316% as abundant as in the Sun's atmosphere. The high surface content of metallic elements is unlikely to be true of the entire star; rather the iron-peak and heavy metals are radiatively levitated towards the surface.[88]

Sirius B

 
Size comparison of Sirius B and Earth

Sirius B is one of the most massive white dwarfs known. With a mass of 1.02 M, it is almost double the 0.5–0.6 M average. This mass is packed into a volume roughly equal to the Earth's.[55] The current surface temperature is 25,200 K.[13] Because there is no internal heat source, Sirius B will steadily cool as the remaining heat is radiated into space over more than two billion years.[94]

A white dwarf forms after a 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, around 120 million years ago. The original star had an estimated 5 M[13] and was a B-type star (most likely B5V for 5 M)[95][96] when it was still on the main sequence, potentially burning around 600-1200 times more luminous than the sun. While it passed through the red giant stage, Sirius B may have enriched the metallicity of its companion, explaining the very high metallicity of Sirius A.

This star is primarily composed of a carbon–oxygen mixture that was generated by helium fusion in the progenitor star.[13] This is overlaid by an envelope of lighter elements, with the materials segregated by mass because of the high surface gravity.[97] The outer atmosphere of Sirius B is now almost pure hydrogen—the element with the lowest mass—and no other elements are seen in its spectrum.[98]

Apparent third star

Since 1894, irregularities have been tentatively observed in the orbits of Sirius A and B with an apparent periodicity of 6–6.4 years. A 1995 study concluded that such a companion likely exists, with a mass of roughly 0.05 solar mass—a small red dwarf or large brown dwarf, with an apparent magnitude of more than 15, and less than 3 arcseconds from Sirius A.[50]

More recent (and accurate) astrometric observations by the Hubble Space Telescope ruled out the existence of such a Sirius C entirely. The 1995 study predicted an astrometric movement of roughly 90 mas (0.09 arcsecond), but Hubble was unable to detect any location anomaly to an accuracy of 5 mas (0.005 arcsec). This ruled out any objects orbiting Sirius A with more than 0.033 solar mass (35 Jupiter masses) orbiting in 0.5 years, and 0.014 (15 Jupiter masses) in 2 years. The study was also able to rule out any companions to Sirius B with more than 0.024 solar mass (25 Jupiter masses) orbiting in 0.5 year, and 0.0095 (10 Jupiter masses) orbiting in 1.8 years. Effectively, there are almost certainly no additional bodies in the Sirius system larger than a small brown dwarf or large exoplanet.[99][12]

Star cluster membership

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. It was once a member of an open cluster, but has since become gravitationally unbound from the cluster.[100] 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, whereas 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.[13][101][102] 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.[103] This would be one of three large clusters located within 500 light-years (150 pc) of the Sun. The other two are the Hyades and the Pleiades, and each of these clusters consists of hundreds of stars.[104]

Distant star cluster

In 2017, a massive star cluster was discovered only 10 arcminutes from Sirius, making the two appear to be visually close to one other when viewed from the point of view of the Earth. It was discovered during a statistical analysis of Gaia data. The cluster is over a thousand times further away from us than the star system, but given its size it still appears at magnitude 8.3.[105]

Etymology

 
A bust of Sopdet, Egyptian goddess of Sirius and the fertility of the Nile, syncretized with Isis and Demeter

The proper name "Sirius" comes from the Latin Sīrius, from the Ancient Greek Σείριος (Seirios, "glowing" or "scorcher").[106] The Greek word itself may have been imported from elsewhere before the Archaic period,[107] one authority suggesting a link with the Egyptian god Osiris.[108] The name's earliest recorded use dates from the 7th century BC in Hesiod's poetic work Works and Days.[107] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[109] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[110] included a table of the first two batches of names approved by the WGSN, which included Sirius for the star α Canis Majoris A. It is now so entered in the IAU Catalog of Star Names.[111]

Sirius has over 50 other designations and names attached to it.[70] In Geoffrey Chaucer's essay Treatise on the Astrolabe, it bears the name Alhabor and is depicted by a hound's head. This name is widely used on medieval astrolabes from Western Europe.[20] In Sanskrit it is known as Mrgavyadha "deer hunter", or Lubdhaka "hunter". As Mrgavyadha, the star represents Rudra (Shiva).[112][113] The star is referred to as Makarajyoti in Malayalam and has religious significance to the pilgrim center Sabarimala.[114] In Scandinavia, the star has been known as Lokabrenna ("burning done by Loki", or "Loki's torch").[115] In the astrology of the Middle Ages, Sirius was a Behenian fixed star,[116] associated with beryl and juniper. Its astrological symbol   was listed by Heinrich Cornelius Agrippa.[117]

Cultural significance

Many cultures have historically attached special significance to Sirius, particularly in relation to dogs. It is often colloquially called the "Dog Star" as the brightest star of Canis Major, the "Great Dog" constellation. Canis Major was classically depicted as Orion's dog. The Ancient Greeks thought that Sirius's emanations could affect dogs adversely, making them behave abnormally during the "dog days", the hottest days of the summer. The Romans knew these days as dies caniculares, and the star Sirius was called Canicula, "little dog". The excessive panting of dogs in hot weather was thought to place them at risk of desiccation and disease. In extreme cases, a foaming dog might have rabies, which could infect and kill humans they had bitten.[30] Homer, in the Iliad, describes the approach of Achilles toward Troy in these words:[118]

Sirius rises late in the dark, liquid sky
On summer nights, star of stars,
Orion's Dog they call it, brightest
Of all, but an evil portent, bringing heat
And fevers to suffering humanity.

In Iranian mythology, especially in Persian mythology and in Zoroastrianism, the ancient religion of Persia, Sirius appears as Tishtrya and is revered as the rain-maker divinity (Tishtar of New Persian poetry). Beside passages in the sacred texts of the Avesta, the Avestan language Tishtrya followed by the version Tir in Middle and New Persian is also depicted in the Persian epic Shahnameh of Ferdowsi. Because of the concept of the yazatas, powers which are "worthy of worship", Tishtrya is a divinity of rain and fertility and an antagonist of apaosha, the demon of drought. In this struggle, Tishtrya is depicted as a white horse.[119][120][121][122]

In Chinese astronomy Sirius is known as the star of the "celestial wolf" (Chinese and Japanese: 天狼 Chinese romanization: Tiānláng; Japanese romanization: Tenrō;[123] Korean and romanization: 천랑 /Tsŏnrang) in the Mansion of Jǐng (井宿). Many nations among the indigenous peoples of North America also associated Sirius with canines; the Seri and Tohono Oʼodham of the southwest note the star as a dog that follows mountain sheep, while the Blackfoot called it "Dog-face". The Cherokee paired Sirius with Antares as a dog-star guardian of either end of the "Path of Souls". The Pawnee of Nebraska had several associations; the Wolf (Skidi) tribe knew it as the "Wolf Star", while other branches knew it as the "Coyote Star". Further north, the Alaskan Inuit of the Bering Strait called it "Moon Dog".[124]

Several cultures also associated the star with a bow and arrows. The ancient Chinese visualized a large bow and arrow across the southern sky, formed by the constellations of Puppis and Canis Major. In this, the arrow tip is pointed at the wolf Sirius. A similar association is depicted at the Temple of Hathor in Dendera, where the goddess Satet has drawn her arrow at Hathor (Sirius). Known as "Tir", the star was portrayed as the arrow itself in later Persian culture.[125]

Sirius is mentioned in Surah, An-Najm ("The Star"), of the Qur'an, where it is given the name الشِّعْرَى (transliteration: aš-ši'rā or ash-shira; the leader).[126] The verse is: "وأنَّهُ هُوَ رَبُّ الشِّعْرَى", "That He is the Lord of Sirius (the Mighty Star)." (An-Najm:49)[127] Ibn Kathir said in his commentary "that it is the bright star, named Mirzam Al-Jawza' (Sirius), which a group of Arabs used to worship".[128] The alternate name Aschere, used by Johann Bayer, is derived from this.[19]

 
Sirius midnight culmination at New Year 2022 local solar time[129]

In theosophy, it is believed the Seven Stars of the Pleiades transmit the spiritual energy of the Seven Rays from the Galactic Logos to the Seven Stars of the Great Bear, then to Sirius. From there is it sent via the Sun to the god of Earth (Sanat Kumara), and finally through the seven Masters of the Seven Rays to the human race.[130]

The midnight culmination of Sirius in the northern hemisphere coincides with the beginning of the New Year[129] of the Gregorian Calendar during the decades around the year 2000. Over the years, its midnight culmination moves slowly, owing to the combination of the star's proper motion and the precession of the equinoxes. At the time of the introduction of the Gregorian calendar in the year 1582, its culmination occurred 17 minutes before midnight into the new year under the assumption of a constant motion. According to Richard Hinckley Allen[131] its mightnight culmination was celebrated at the Temple of Demeter at Eleusis.

Dogon

The Dogon people are an ethnic group in Mali, West Africa, reported by some researchers to have traditional astronomical knowledge about Sirius that would normally be considered impossible without the use of telescopes. According to Marcel Griaule, they knew about the fifty-year orbital period of Sirius and its companion prior to western astronomers.[132][133]

Doubts have been raised about the validity of Griaule and Dieterlein's work.[134][135] In 1991, anthropologist Walter van Beek concluded about the Dogon, "Though they do speak about sigu tolo [which is what Griaule claimed the Dogon called Sirius] they disagree completely with each other as to which star is meant; for some it is an invisible star that should rise to announce the sigu [festival], for another it is Venus that, through a different position, appears as sigu tolo. All agree, however, that they learned about the star from Griaule."[136] According to Noah Brosch cultural transfer of relatively modern astronomical information could have taken place in 1893, when a French expedition arrived in Central West Africa to observe the total eclipse on 16 April.[137]

In his pseudoarcheology book The Sirius Mystery, Robert Temple claimed that the Dogon people have a tradition of contact with intelligent extraterrestrial beings from Sirius.[138]

Serer religion

 
Yoonir, symbol of the universe in Serer religion[139][140]

In the religion of the Serer people of Senegal, the Gambia and Mauritania, Sirius is called Yoonir from the Serer language (and some of the Cangin language speakers, who are all ethnically Serers). The star Sirius is one of the most important and sacred stars in Serer religious cosmology and symbolism. The Serer high priests and priestesses (Saltigues, the hereditary "rain priests"[141]) chart Yoonir in order to forecast rainfall and enable Serer farmers to start planting seeds. In Serer religious cosmology, it is the symbol of the universe.[139][140]

Modern significance

Sirius features on the coat of arms of Macquarie University, and is the name of its alumnae journal.[142] Seven ships of the Royal Navy have been called HMS Sirius since the 18th century, with the first being the flagship of the First Fleet to Australia in 1788.[143] The Royal Australian Navy subsequently named a vessel HMAS Sirius in honor of the flagship.[144] American vessels include the USNS Sirius (T-AFS-8) as well as a monoplane model—the Lockheed Sirius, the first of which was flown by Charles Lindbergh.[145] The name was also adopted by Mitsubishi Motors as the Mitsubishi Sirius engine in 1980.[146] The name of the North American satellite radio company CD Radio was changed to Sirius Satellite Radio in November 1999, being named after "the brightest star in the night sky".[147] Sirius is one of the 27 stars on the flag of Brazil, where it represents the state of Mato Grosso.[148]

Composer Karlheinz Stockhausen, who wrote a piece called Sirius, is claimed to have said on several occasions that he came from a planet in the Sirius system.[149][150] To Stockhausen, Sirius stood for "the place where music is the highest of vibrations" and where music had been developed in the most perfect way.[151]

Sirius has been the subject of poetry.[152] Dante and John Milton reference the star, and it is the "powerful western fallen star" of Walt Whitman's "When Lilacs Last in the Dooryard Bloom'd", while Tennyson's poem The Princess describes the star's scintillation:

...the fiery Sirius alters hue
And bickers into red and emerald.[153]

See also

Notes

  1. ^ Compare the meaning of the Egyptian name with Sirius's completion of the Winter Triangle asterism, joining the other two brightest stars of the northern winter sky, Betelgeuse and Procyon.
  2. ^ As Sirius is visible together with the constellation of Orion, the Egyptians worshipped Orion as the god Sah, the husband of Sopdet, with whom she had a son, the sky god Sopdu. The goddess Sopdet was later syncretized with the goddess Isis, Sah was linked with Osiris, and Sopdu was linked with Horus. The joining of Sopdet with Isis would allow Plutarch to state that "The soul of Isis is called Dog by the Greeks", meaning Sirius worshipped as Isis-Sopdet by Egyptians was named the Dog by the Greeks and Romans. The 70-day period of the absence of Sirius from the sky was understood as the passing of Sopdet-Isis and Sah-Osiris through the Egyptian underworld.[28]
  3. ^ Two full 50.09-year orbits following the periastron epoch of 1894.13 gives a date of 1994.31.
  4. ^ Two and one-half 50.09-year orbits following the periastron epoch of 1894.13 gives a date of 2019.34.
  5. ^ Semi-major axis in AU = semimajor axis in seconds / parallax = 7.56″ / 0.37921 = 19.8 AU; as the eccentricity is 0.6, the distance fluctuates between 40% and 160% of that, roughly from 8 AU to 32 AU.

References

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Bibliography

  • Brosch, Noah (2008). Sirius Matters. Astrophysics and Space Science Library. Vol. 354. doi:10.1007/978-1-4020-8319-8_10. ISBN 978-1-4020-8318-1.
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  • Makemson, Maud Worcester (1941). The Morning Star Rises: An Account of Polynesian Astronomy. Yale University Press. Bibcode:1941msra.book.....M.

External links

  • NASA Astronomy Picture of the Day: Sirius B in x-ray (6 October 2000)
  • "Sirius Matters: Alien Contact". Chandra X-ray Center. 28 November 2000. Retrieved 21 March 2021.
  • Sankey, John. "Getting Sirius About Time". www.johnsankey.ca. Retrieved 21 March 2021.
  • Barker, Tho.; Stukeley, W. (1760). "Remarks on the Mutations of the Stars". Philosophical Transactions. 51: 498–504. doi:10.1098/rstl.1759.0049. JSTOR 105393.

sirius, several, terms, redirect, here, other, uses, disambiguation, disambiguation, star, disambiguation, brightest, star, night, name, derived, from, greek, word, Σείριος, seirios, meaning, glowing, scorching, star, designated, canis, majoris, latinized, alp. Several terms redirect here For other uses see Sirius disambiguation Sirius B disambiguation and Dog Star disambiguation Sirius is the brightest star in the night sky Its name is derived from the Greek word Seirios or Seirios meaning lit glowing or scorching The star is designated a Canis Majoris Latinized to Alpha Canis Majoris and abbreviated Alpha CMa or a CMa With a visual apparent magnitude of 1 46 Sirius is almost twice as bright as Canopus the next brightest star Sirius is a binary star consisting of a main sequence star of spectral type A0 or A1 termed Sirius A and a faint white dwarf companion of spectral type DA2 termed Sirius B The distance between the two varies between 8 2 and 31 5 astronomical units as they orbit every 50 years 25 SiriusLocation of Sirius circled Observation dataEpoch J2000 0 Equinox ICRSConstellation Canis MajorPronunciation ˈ s ɪr i e s 1 Sirius ARight ascension 06h 45m 08 917s 2 Declination 16 42 58 02 2 Apparent magnitude V 1 46 3 Sirius BRight ascension 06h 45m 09 0s 4 Declination 16 43 06 4 Apparent magnitude V 8 44 5 CharacteristicsSirius AEvolutionary stage Main sequenceSpectral type A0mA1 Va 6 U B colour index 0 05 3 B V colour index 0 00 3 Sirius BEvolutionary stage White dwarfSpectral type DA2 5 U B colour index 1 04 7 B V colour index 0 03 7 AstrometryRadial velocity Rv 5 50 8 km sSirius AProper motion m RA 546 01 mas yr 9 Dec 1 223 07 mas yr 9 Parallax p 379 21 1 58 mas 9 Distance8 60 0 04 ly 2 64 0 01 pc Absolute magnitude MV 1 43 10 Sirius BProper motion m RA 461 571 mas yr 11 Dec 914 520 mas yr 11 Parallax p 374 4896 0 2313 mas 11 Distance8 709 0 005 ly 2 670 0 002 pc Absolute magnitude MV 11 18 7 Orbit 12 Primarya Canis Majoris ACompaniona Canis Majoris BPeriod P 50 1284 0 0043 yrSemi major axis a 7 4957 0 0025 Eccentricity e 0 59142 0 00037Inclination i 136 336 0 040 Longitude of the node W 45 400 0 071 Periastron epoch T 1 994 5715 0 0058Argument of periastron w secondary 149 161 0 075 DetailsSirius AMass2 063 0 023 12 M Radius1 711 13 R Luminosity25 4 13 L Surface gravity log g 4 33 14 cgsTemperature9 940 14 KMetallicity Fe H 0 50 15 dexRotational velocity v sin i 16 16 km sAge242 5 12 MyrSirius BMass1 018 0 011 12 M Radius0 0084 3 17 R Luminosity0 056 18 L Surface gravity log g 8 57 17 cgsTemperature25 000 200 13 KAge228 10 8 12 MyrOther designationsDog Star Aschere Canicula Al Shira Sothis 19 Alhabor 20 Mrgavyadha Lubdhaka 21 Tenrōsei 22 a Canis Majoris a CMa 9 Canis Majoris 9 CMa HD 48915 HR 2491 BD 16 1591 GJ 244 LHS 219 ADS 5423 LTT 2638 HIP 32349 23 Sirius B EGGR 49 WD 0642 166 GCTP 1577 00 24 Database referencesABSirius appears bright because of its intrinsic luminosity and its proximity to the Solar System At a distance of 2 64 parsecs 8 6 ly the Sirius system is one of Earth s nearest neighbours Sirius is gradually moving closer to the Solar System so it is expected to increase in brightness slightly over the next 60 000 years reaching a peak magnitude of 1 68 After that time its distance will begin to increase and it will become fainter but it will continue to be the brightest star in the Earth s night sky for approximately the next 210 000 years before Vega another A type star and more luminous than Sirius becomes the brightest star 26 Sirius A is about twice as massive as the Sun M and has an absolute visual magnitude of 1 43 It is 25 times as luminous as the Sun 13 but has a significantly lower luminosity than other bright stars such as Canopus Betelgeuse or Rigel The system is between 200 and 300 million years old 13 It was originally composed of two bright bluish stars The initially more massive of these Sirius B consumed its hydrogen fuel 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 13 Sirius is colloquially known as the Dog Star reflecting its prominence in its constellation Canis Major the Greater Dog 19 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 mostly in the Southern Hemisphere the star marked winter and was an important reference for their navigation around the Pacific Ocean Contents 1 Observational history 1 1 Kinematics 1 2 Distance 1 3 Discovery of Sirius B 1 4 Colour controversy 2 Observation 3 Stellar system 3 1 Sirius A 3 2 Sirius B 3 3 Apparent third star 3 4 Star cluster membership 3 5 Distant star cluster 4 Etymology 5 Cultural significance 5 1 Dogon 5 2 Serer religion 5 3 Modern significance 6 See also 7 Notes 8 References 8 1 Citations 8 2 Bibliography 9 External linksObservational history EditSiriusSpdtEgyptian hieroglyphsThe brightest star seen from Earth Sirius is recorded in some of the earliest astronomical records Its displacement from the ecliptic causes its heliacal rising to be remarkably regular compared to other stars with a period of almost exactly 365 25 days holding it constant relative to the solar year This rising occurs at Cairo on 19 July Julian placing it just before the onset of the annual flooding of the Nile during antiquity 27 Owing to the flood s own irregularity the extreme precision of the star s return made it important to the ancient Egyptians 27 who worshipped it as the goddess Sopdet Ancient Egyptian Spdt Triangle a Greek Sῶ8is Sō this guarantor of the fertility of their land b The ancient Greeks observed that the appearance of Sirius as the morning star heralded the hot and dry summer and feared that the star caused plants to wilt men to weaken and women to become aroused 29 Owing to its brightness Sirius would have been seen to twinkle more in the unsettled weather conditions of early summer To Greek observers this signified emanations that caused its malignant influence Anyone suffering its effects was said to be star struck ἀstrobolhtos astroboletos It was described as burning or flaming in literature 30 The season following the star s reappearance came to be known as the dog days 31 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 3rd century BC feature dogs or stars with emanating rays highlighting Sirius s importance 30 The Romans celebrated the heliacal setting of Sirius around 25 April 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 32 Bright stars were important to the ancient Polynesians for navigation of the Pacific Ocean They also served as latitude markers the declination of Sirius matches the latitude of the archipelago of Fiji at 17 S and thus passes directly over the islands each sidereal day 33 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 34 Just as the appearance of Sirius in the morning sky marked summer in Greece it marked the onset of winter for the Maori 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 Ta urua fau papa Festivity of original high chiefs and Ta urua e hiti i te tara te feiai Festivity who rises with prayers and religious ceremonies in Tahiti 35 Kinematics Edit In 1717 Edmond Halley discovered the proper motion of the hitherto presumed fixed stars 36 after comparing contemporary astrometric measurements with those from the second century AD given in Ptolemy s Almagest The bright stars Aldebaran Arcturus and Sirius were noted to have moved significantly Sirius had progressed about 30 arcminutes about the diameter of the Moon to the southwest 37 In 1868 Sirius became the first star to have its velocity measured the beginning of the study of celestial radial velocities Sir William Huggins examined the spectrum of the star and observed a red shift He concluded that Sirius was receding from the Solar System at about 40 km s 38 39 Compared to the modern value of 5 5 km s this was an overestimate and had the wrong sign the minus sign means that it is approaching the Sun 40 Distance Edit In his 1698 book Cosmotheoros Christiaan Huygens estimated the distance to Sirius at 27 664 times the distance from the Earth to the Sun about 0 437 light year translating to a parallax of roughly 7 5 arcseconds 41 There were several unsuccessful attempts to measure the parallax of Sirius by Jacques Cassini 6 seconds by some astronomers including Nevil Maskelyne 42 using Lacaille s observations made at the Cape of Good Hope 4 seconds by Piazzi the same amount using Lacaille s observations made at Paris more numerous and certain than those made at the Cape no sensible parallax by Bessel no sensible parallax 43 Scottish astronomer Thomas Henderson used his observations made in 1832 1833 and South African astronomer Thomas Maclear s observations made in 1836 1837 to determine that the value of the parallax was 0 23 arcsecond and error of the parallax was estimated not to exceed a quarter of a second or as Henderson wrote in 1839 On the whole we may conclude that the parallax of Sirius is not greater than half a second in space and that it is probably much less 44 Astronomers adopted a value of 0 25 arcsecond for much of the 19th century 45 It is now known to have a parallax of nearly 0 4 arcseconds The Hipparcos parallax for Sirius is only accurate to about 0 04 light years giving a distance of 8 6 light years 9 Sirius B is generally assumed to be at the same distance Sirius B has a Gaia Data Release 3 parallax with a much smaller statistical margin of error giving a distance of 8 709 0 005 light years but it is flagged as having a very large value for astrometric excess noise which indicates that the parallax value may be unreliable 11 Discovery of Sirius B Edit Hubble Space Telescope image of Sirius A and Sirius B The white dwarf can be seen to the lower left The diffraction spikes and concentric rings are instrumental effects In a letter dated 10 August 1844 the German astronomer Friedrich Wilhelm Bessel deduced from changes in the proper motion of Sirius that it had an unseen companion 46 On 31 January 1862 American telescope maker and astronomer Alvan Graham Clark first observed the faint companion which is now called Sirius B or affectionately the Pup 47 This happened during testing of an 18 5 inch 470 mm aperture great refractor telescope for Dearborn Observatory which was one of the largest refracting telescope lenses in existence at the time and the largest telescope in the United States 48 Sirius B s sighting was confirmed on 8 March with smaller telescopes 49 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 confirmed The best fit to the data indicates a six year orbit around Sirius A and a mass of 0 06 M This star would be five to ten magnitudes fainter than the white dwarf Sirius B which would make it difficult to observe 50 Observations published in 2008 were unable to detect either a third star or a planet An apparent third star observed in the 1920s is now believed to be a background object 51 In 1915 Walter Sydney Adams using a 60 inch 1 5 m reflector at Mount Wilson Observatory observed the spectrum of Sirius B and determined that it was a faint whitish star 52 This led astronomers to conclude that it was a white dwarf the second to be discovered 53 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 54 In 2005 using the Hubble Space Telescope astronomers determined that Sirius B has nearly the diameter of the Earth 12 000 kilometres 7 500 mi with a mass 102 of the Sun s 55 Colour controversy Edit source source source source source source source source source source Twinkling of Sirius apparent magnitude 1 5 in the evening shortly before upper culmination on the southern meridian at a height of 20 degrees above the horizon During 29 seconds Sirius moves on an arc of 7 5 minutes from the left to the right Around the year 150 AD 56 the Greek astronomer of the Roman period Ptolemy of Alexandria mapped the stars in Books VII and VIII of his Almagest in which he used Sirius as the location for the globe s central meridian 57 He described Sirius as reddish along with five other stars Betelgeuse Antares Aldebaran Arcturus and Pollux all of which are of orange or red hue 56 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 58 The existence of other stars changing in brightness gave credibility 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 59 Thomas Jefferson Jackson See resurrected discussion on red Sirius with the publication of several papers in 1892 and a final summary in 1926 60 He cited not only Ptolemy but also the poet Aratus the orator Cicero and general Germanicus as calling the star red though acknowledging that none of the latter three authors were astronomers the last two merely translating Aratus s poem Phaenomena 61 Seneca had described Sirius as being of a deeper red than Mars 62 Not all ancient observers saw Sirius as red The 1st century poet Marcus Manilius described it as sea blue as did the 4th century Avienius 63 It was the standard white star in ancient China and multiple records from the 2nd century BC up to the 7th century AD all describe Sirius as white 64 65 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 a bright star described as rubeola reddish was claimed to be Sirius The authors proposed this was further evidence Sirius B had been a red giant at the time 66 Other scholars replied that it was likely St Gregory had been referring to Arcturus 67 68 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 much too short and that there is no sign of the nebulosity in the system that would be expected had such a change taken place 62 An interaction with a third star to date undiscovered has also been proposed as a possibility for a red appearance 69 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 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 62 Observation Edit Sirius bottom and the constellation Orion right The three brightest stars in this image Sirius Betelgeuse top right and Procyon top left form the Winter Triangle The bright star at top center is Alhena which forms a cross shaped asterism with the Winter Triangle With an apparent magnitude of 1 46 Sirius is the brightest star in the night sky almost twice as bright as the second brightest star Canopus 70 From Earth Sirius always appears dimmer than Jupiter and Venus as well as Mercury and Mars at certain times 71 Sirius is visible from almost everywhere on Earth except latitudes north of 73 N and it does not rise very high when viewed from some northern cities reaching only 13 above the horizon from Saint Petersburg 72 Because of its declination of roughly 17 Sirius is a circumpolar star from latitudes south of 73 S From the Southern Hemisphere in early July Sirius can be seen in both the evening where it sets after the Sun and in the morning where it rises before the Sun 73 Along with Procyon and Betelgeuse Sirius forms one of the three vertices of the Winter Triangle to observers in the Northern Hemisphere 74 Sirius can 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 on the horizon These observing conditions are more easily met in the Southern Hemisphere owing to the southerly declination of Sirius 75 The orbital motion of the Sirius binary system brings the two stars to a minimum angular separation of 3 arcseconds and a maximum of 11 arcseconds 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 After a periastron occurred in 1994 c the pair moved apart making them easier to separate with a telescope 76 Apoastron occurred in 2019 d but from the Earth s vantage point the greatest observational separation will occur in 2023 with an angular separation of 11 333 77 At a distance of 2 6 parsecs 8 6 ly the Sirius system contains two of the eight nearest stars to the Sun and it is the fifth closest stellar system to the Sun 78 This proximity is the main reason for its brightness as with other near stars such as Alpha Centauri Procyon and Vega and in contrast to distant highly luminous supergiants such as Canopus Rigel or Betelgeuse Note that Canopus may be a bright giant 79 It is still around 25 times more luminous than the Sun 13 The closest large neighbouring star to Sirius is Procyon 1 61 parsecs 5 24 ly away 80 The Voyager 2 spacecraft launched in 1977 to study the four giant planets in the Solar System is expected to pass within 4 3 light years 1 3 pc of Sirius in approximately 296 000 years 81 Stellar system Edit The orbit of Sirius B around A as seen from Earth slanted ellipse The wide horizontal ellipse shows the true shape of the orbit with an arbitrary orientation as it would appear if viewed straight on A Chandra X ray Observatory image of the Sirius star system where the spike like pattern is due to the support structure for the transmission grating The bright source is Sirius B Credit NASA SAO CXC Sirius is a binary star system consisting of two white stars orbiting each other with a separation of about 20 AU e roughly the distance between the Sun and Uranus and a period of 50 1 years The brighter component termed Sirius A is a main sequence star of spectral type early A with an estimated surface temperature of 9 940 K 14 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 82 The age of the system has been estimated at around 230 million years Early in its life it is thought to have been two bluish white stars orbiting each other in an elliptical orbit every 9 1 years 82 The system emits a higher than expected level of infrared radiation as measured by IRAS space based observatory This might be an indication of dust in the system which is considered somewhat unusual for a binary star 80 83 The Chandra X ray Observatory image shows Sirius B outshining its partner as an X ray source 84 In 2015 Vigan and colleagues used the VLT Survey Telescope to search for evidence of substellar companions and were able to rule out the presence of giant planets 11 times more massive than Jupiter at 0 5 AU distance from Sirius A 6 7 times the mass of Jupiter at 1 2 AU distance and down to around 4 times the mass of Jupiter at 10 AU distance 85 Similarly Lucas and colleagues did not detect any companions around Sirius B 86 Sirius A Edit Comparison of Sirius A and the Sun to scale and relative surface brightness Sirius A has a mass of 2 063 M 12 13 87 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 16 which does not produce any significant flattening of its disk 88 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 89 A weak magnetic field has been detected on the surface of Sirius A 90 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 used the CNO cycle for energy generation 88 It is calculated that Sirius A will have completely exhausted the store of hydrogen at its core within a billion 109 years of its formation and will then evolve away from the main sequence 91 It will pass through a red giant stage and eventually become a white dwarf 92 Sirius A is classed as an Am star because the spectrum shows deep metallic absorption lines 93 indicating an enhancement of its surface layers in elements heavier than helium such as iron 80 88 The spectral type has been reported as A0mA1 Va which indicates that it would be classified as A1 from hydrogen and helium lines but A0 from the metallic lines that cause it to be grouped with the Am stars 6 When compared to the Sun the proportion of iron in the atmosphere of Sirius A relative to hydrogen is given by Fe H 0 5 displaystyle textstyle left frac ce Fe ce H right 0 5 15 meaning iron is 316 as abundant as in the Sun s atmosphere The high surface content of metallic elements is unlikely to be true of the entire star rather the iron peak and heavy metals are radiatively levitated towards the surface 88 Sirius B Edit Size comparison of Sirius B and Earth Sirius B is one of the most massive white dwarfs known With a mass of 1 02 M it is almost double the 0 5 0 6 M average This mass is packed into a volume roughly equal to the Earth s 55 The current surface temperature is 25 200 K 13 Because there is no internal heat source Sirius B will steadily cool as the remaining heat is radiated into space over more than two billion years 94 A white dwarf forms after a 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 around 120 million years ago The original star had an estimated 5 M 13 and was a B type star most likely B5V for 5 M 95 96 when it was still on the main sequence potentially burning around 600 1200 times more luminous than the sun While it passed through the red giant stage Sirius B may have enriched the metallicity of its companion explaining the very high metallicity of Sirius A This star is primarily composed of a carbon oxygen mixture that was generated by helium fusion in the progenitor star 13 This is overlaid by an envelope of lighter elements with the materials segregated by mass because of the high surface gravity 97 The outer atmosphere of Sirius B is now almost pure hydrogen the element with the lowest mass and no other elements are seen in its spectrum 98 Apparent third star Edit Since 1894 irregularities have been tentatively observed in the orbits of Sirius A and B with an apparent periodicity of 6 6 4 years A 1995 study concluded that such a companion likely exists with a mass of roughly 0 05 solar mass a small red dwarf or large brown dwarf with an apparent magnitude of more than 15 and less than 3 arcseconds from Sirius A 50 More recent and accurate astrometric observations by the Hubble Space Telescope ruled out the existence of such a Sirius C entirely The 1995 study predicted an astrometric movement of roughly 90 mas 0 09 arcsecond but Hubble was unable to detect any location anomaly to an accuracy of 5 mas 0 005 arcsec This ruled out any objects orbiting Sirius A with more than 0 033 solar mass 35 Jupiter masses orbiting in 0 5 years and 0 014 15 Jupiter masses in 2 years The study was also able to rule out any companions to Sirius B with more than 0 024 solar mass 25 Jupiter masses orbiting in 0 5 year and 0 0095 10 Jupiter masses orbiting in 1 8 years Effectively there are almost certainly no additional bodies in the Sirius system larger than a small brown dwarf or large exoplanet 99 12 Star cluster membership Edit 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 It was once a member of an open cluster but has since become gravitationally unbound from the cluster 100 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 whereas 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 13 101 102 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 103 This would be one of three large clusters located within 500 light years 150 pc of the Sun The other two are the Hyades and the Pleiades and each of these clusters consists of hundreds of stars 104 Distant star cluster Edit Main article Gaia 1 In 2017 a massive star cluster was discovered only 10 arcminutes from Sirius making the two appear to be visually close to one other when viewed from the point of view of the Earth It was discovered during a statistical analysis of Gaia data The cluster is over a thousand times further away from us than the star system but given its size it still appears at magnitude 8 3 105 Etymology EditSee also Winter Triangle A bust of Sopdet Egyptian goddess of Sirius and the fertility of the Nile syncretized with Isis and Demeter The proper name Sirius comes from the Latin Sirius from the Ancient Greek Seirios Seirios glowing or scorcher 106 The Greek word itself may have been imported from elsewhere before the Archaic period 107 one authority suggesting a link with the Egyptian god Osiris 108 The name s earliest recorded use dates from the 7th century BC in Hesiod s poetic work Works and Days 107 In 2016 the International Astronomical Union organized a Working Group on Star Names WGSN 109 to catalog and standardize proper names for stars The WGSN s first bulletin of July 2016 110 included a table of the first two batches of names approved by the WGSN which included Sirius for the star a Canis Majoris A It is now so entered in the IAU Catalog of Star Names 111 Sirius has over 50 other designations and names attached to it 70 In Geoffrey Chaucer s essay Treatise on the Astrolabe it bears the name Alhabor and is depicted by a hound s head This name is widely used on medieval astrolabes from Western Europe 20 In Sanskrit it is known as Mrgavyadha deer hunter or Lubdhaka hunter As Mrgavyadha the star represents Rudra Shiva 112 113 The star is referred to as Makarajyoti in Malayalam and has religious significance to the pilgrim center Sabarimala 114 In Scandinavia the star has been known as Lokabrenna burning done by Loki or Loki s torch 115 In the astrology of the Middle Ages Sirius was a Behenian fixed star 116 associated with beryl and juniper Its astrological symbol was listed by Heinrich Cornelius Agrippa 117 Cultural significance EditMany cultures have historically attached special significance to Sirius particularly in relation to dogs It is often colloquially called the Dog Star as the brightest star of Canis Major the Great Dog constellation Canis Major was classically depicted as Orion s dog The Ancient Greeks thought that Sirius s emanations could affect dogs adversely making them behave abnormally during the dog days the hottest days of the summer The Romans knew these days as dies caniculares and the star Sirius was called Canicula little dog The excessive panting of dogs in hot weather was thought to place them at risk of desiccation and disease In extreme cases a foaming dog might have rabies which could infect and kill humans they had bitten 30 Homer in the Iliad describes the approach of Achilles toward Troy in these words 118 Sirius rises late in the dark liquid sky On summer nights star of stars Orion s Dog they call it brightest Of all but an evil portent bringing heat And fevers to suffering humanity In Iranian mythology especially in Persian mythology and in Zoroastrianism the ancient religion of Persia Sirius appears as Tishtrya and is revered as the rain maker divinity Tishtar of New Persian poetry Beside passages in the sacred texts of the Avesta the Avestan language Tishtrya followed by the version Tir in Middle and New Persian is also depicted in the Persian epic Shahnameh of Ferdowsi Because of the concept of the yazatas powers which are worthy of worship Tishtrya is a divinity of rain and fertility and an antagonist of apaosha the demon of drought In this struggle Tishtrya is depicted as a white horse 119 120 121 122 In Chinese astronomy Sirius is known as the star of the celestial wolf Chinese and Japanese 天狼 Chinese romanization Tianlang Japanese romanization Tenrō 123 Korean and romanization 천랑 Tsŏnrang in the Mansion of Jǐng 井宿 Many nations among the indigenous peoples of North America also associated Sirius with canines the Seri and Tohono Oʼodham of the southwest note the star as a dog that follows mountain sheep while the Blackfoot called it Dog face The Cherokee paired Sirius with Antares as a dog star guardian of either end of the Path of Souls The Pawnee of Nebraska had several associations the Wolf Skidi tribe knew it as the Wolf Star while other branches knew it as the Coyote Star Further north the Alaskan Inuit of the Bering Strait called it Moon Dog 124 Several cultures also associated the star with a bow and arrows The ancient Chinese visualized a large bow and arrow across the southern sky formed by the constellations of Puppis and Canis Major In this the arrow tip is pointed at the wolf Sirius A similar association is depicted at the Temple of Hathor in Dendera where the goddess Satet has drawn her arrow at Hathor Sirius Known as Tir the star was portrayed as the arrow itself in later Persian culture 125 Sirius is mentioned in Surah An Najm The Star of the Qur an where it is given the name الش ع ر ى transliteration as si ra or ash shira the leader 126 The verse is وأن ه ه و ر ب الش ع ر ى That He is the Lord of Sirius the Mighty Star An Najm 49 127 Ibn Kathir said in his commentary that it is the bright star named Mirzam Al Jawza Sirius which a group of Arabs used to worship 128 The alternate name Aschere used by Johann Bayer is derived from this 19 Sirius midnight culmination at New Year 2022 local solar time 129 In theosophy it is believed the Seven Stars of the Pleiades transmit the spiritual energy of the Seven Rays from the Galactic Logos to the Seven Stars of the Great Bear then to Sirius From there is it sent via the Sun to the god of Earth Sanat Kumara and finally through the seven Masters of the Seven Rays to the human race 130 The midnight culmination of Sirius in the northern hemisphere coincides with the beginning of the New Year 129 of the Gregorian Calendar during the decades around the year 2000 Over the years its midnight culmination moves slowly owing to the combination of the star s proper motion and the precession of the equinoxes At the time of the introduction of the Gregorian calendar in the year 1582 its culmination occurred 17 minutes before midnight into the new year under the assumption of a constant motion According to Richard Hinckley Allen 131 its mightnight culmination was celebrated at the Temple of Demeter at Eleusis Dogon Edit See also Nommo The Dogon people are an ethnic group in Mali West Africa reported by some researchers to have traditional astronomical knowledge about Sirius that would normally be considered impossible without the use of telescopes According to Marcel Griaule they knew about the fifty year orbital period of Sirius and its companion prior to western astronomers 132 133 Doubts have been raised about the validity of Griaule and Dieterlein s work 134 135 In 1991 anthropologist Walter van Beek concluded about the Dogon Though they do speak about sigu tolo which is what Griaule claimed the Dogon called Sirius they disagree completely with each other as to which star is meant for some it is an invisible star that should rise to announce the sigu festival for another it is Venus that through a different position appears as sigu tolo All agree however that they learned about the star from Griaule 136 According to Noah Brosch cultural transfer of relatively modern astronomical information could have taken place in 1893 when a French expedition arrived in Central West Africa to observe the total eclipse on 16 April 137 In his pseudoarcheology book The Sirius Mystery Robert Temple claimed that the Dogon people have a tradition of contact with intelligent extraterrestrial beings from Sirius 138 Serer religion Edit Yoonir symbol of the universe in Serer religion 139 140 Main articles Serer religion and Saltigue In the religion of the Serer people of Senegal the Gambia and Mauritania Sirius is called Yoonir from the Serer language and some of the Cangin language speakers who are all ethnically Serers The star Sirius is one of the most important and sacred stars in Serer religious cosmology and symbolism The Serer high priests and priestesses Saltigues the hereditary rain priests 141 chart Yoonir in order to forecast rainfall and enable Serer farmers to start planting seeds In Serer religious cosmology it is the symbol of the universe 139 140 Modern significance Edit See also Sirius in fiction Sirius features on the coat of arms of Macquarie University and is the name of its alumnae journal 142 Seven ships of the Royal Navy have been called HMS Sirius since the 18th century with the first being the flagship of the First Fleet to Australia in 1788 143 The Royal Australian Navy subsequently named a vessel HMAS Sirius in honor of the flagship 144 American vessels include the USNS Sirius T AFS 8 as well as a monoplane model the Lockheed Sirius the first of which was flown by Charles Lindbergh 145 The name was also adopted by Mitsubishi Motors as the Mitsubishi Sirius engine in 1980 146 The name of the North American satellite radio company CD Radio was changed to Sirius Satellite Radio in November 1999 being named after the brightest star in the night sky 147 Sirius is one of the 27 stars on the flag of Brazil where it represents the state of Mato Grosso 148 Composer Karlheinz Stockhausen who wrote a piece called Sirius is claimed to have said on several occasions that he came from a planet in the Sirius system 149 150 To Stockhausen Sirius stood for the place where music is the highest of vibrations and where music had been developed in the most perfect way 151 Sirius has been the subject of poetry 152 Dante and John Milton reference the star and it is the powerful western fallen star of Walt Whitman s When Lilacs Last in the Dooryard Bloom d while Tennyson s poem The Princess describes the star s scintillation the fiery Sirius alters hue And bickers into red and emerald 153 See also EditList of stars in Canis MajorNotes Edit Compare the meaning of the Egyptian name with Sirius s completion of the Winter Triangle asterism joining the other two brightest stars of the northern winter sky Betelgeuse and Procyon As Sirius is visible together with the constellation of Orion the Egyptians worshipped Orion as the god Sah the husband of Sopdet with whom she had a son the sky god Sopdu The goddess Sopdet was later syncretized with the goddess Isis Sah was linked with Osiris and Sopdu was linked with Horus The joining of Sopdet with Isis would allow Plutarch to state that The soul of Isis is called Dog by the Greeks meaning Sirius worshipped as Isis Sopdet by Egyptians was named the Dog by the Greeks and Romans The 70 day period of the absence of Sirius from the sky was understood as the passing of Sopdet Isis and Sah Osiris through the Egyptian underworld 28 Two full 50 09 year orbits following the periastron epoch of 1894 13 gives a date of 1994 31 Two and one half 50 09 year orbits following the periastron epoch of 1894 13 gives a date of 2019 34 Semi major axis in AU semimajor 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January 2022 Baker Douglas 1977 The Seven Rays Key to the Mysteries Wellingborough Herts Aquarian Press ISBN 0 87728 377 X Allen Richard Hinckley 1899 Star names and Their Meanings G E Stechert p 125 The culmination of this star at midnight was celebrated in the great temple of Ceres at Eleusis Griaule Marcel 1965 Conversations with Ogotemmeli An Introduction to Dogon Religious Ideas ISBN 0 19 519821 2 many reprints Originally published in 1948 as Dieu d Eau Griaule Marcel Dieterlen Germaine 1965 The Pale Fox Institut d Ethnologie Originally published as Le Renard Pale Bernard R Ortiz de Montellano The Dogon Revisited Archived from the original on 16 February 2013 Retrieved 13 October 2007 Philip Coppens Dogon Shame Archived from the original on 27 December 2012 Retrieved 13 October 2007 van Beek W A E Bedaux Blier Bouju Crawford Douglas Lane Meillassoux 1991 Dogon Restudied A Field Evaluation of the Work of Marcel Griaule Current Anthropology 32 2 139 167 doi 10 1086 203932 JSTOR 2743641 S2CID 224796672 Brosch 2008 p 65 Sheppard R Z 2 August 1976 Worlds in Collusion Time Archived from the original on February 20 2011 a b Gravrand Henry La civilisation sereer Pangool vol 2 Les Nouvelles Editions Africaines du Senegal 1990 pp 20 21 149 155 ISBN 2 7236 1055 1 a b Clementine Faik Nzuji Madiya Canadian Museum of Civilization Canadian Centre for Folk Culture Studies International Centre for African Language Literature and Tradition Louvain Belgium ISBN 0 660 15965 1 pp 5 27 115 Galvan Dennis Charles The State Must be our Master of Fire How Peasants Craft Culturally Sustainable Development in Senegal Berkeley University of California Press 2004 pp 86 135 ISBN 978 0 520 23591 5 About Macquarie University Naming of the University Macquarie University official website Macquarie University 2007 Retrieved 27 December 2007 Henderson G Stanbury M 1988 The Sirius Past and Present Sydney Collins p 38 ISBN 0 7322 2447 0 Royal Australian Navy 2006 HMAS Sirius Welcome Aboard Royal Australian Navy Official Site Commonwealth of Australia Retrieved 23 January 2008 Lockheed Sirius Tingmissartoq Charles A Lindbergh Smithsonian National Air and Space Museum Smithsonian Institution Mitsubishi Motors history Mitsubishi Motors South Africa Official Website Mercedes Benz 2007 Archived from the original on 30 December 2007 Retrieved 27 January 2008 Sirius Satellite Radio Inc Company Profile Information Business Description History Background Information on Sirius Satellite Radio Inc Net Industries LLC Retrieved 22 January 2008 Duarte Paulo Araujo Astronomia na Bandeira Brasileira Universidade Federal de Santa Catarina Archived from the original on 2 May 2008 Retrieved 9 July 2009 McEnery Paul 16 January 2001 Karlheinz Stockhausen Salon com Archived from the original on 3 November 2012 Tom Service 13 October 2005 Beam Me up Stocky The Guardian Michael Kurtz Stockhausen Eine Biografie Kassel Barenreiter Verlag 1988 p 271 Brosch 2008 p 33 Allen Richard Hinckley 1899 Star names and their meanings New York G E Stechert pp 117 131 Bibliography Edit Brosch Noah 2008 Sirius Matters Astrophysics and Space Science Library Vol 354 doi 10 1007 978 1 4020 8319 8 10 ISBN 978 1 4020 8318 1 Holberg J B 2007 Sirius Brightest Diamond in the Night Sky Chichester UK Praxis Publishing ISBN 978 0 387 48941 4 Makemson Maud Worcester 1941 The Morning Star Rises An Account of Polynesian Astronomy Yale University Press Bibcode 1941msra book M External links Edit Look up dog days in Wiktionary the free dictionary Wikimedia Commons has media related to Sirius NASA Astronomy Picture of the Day Sirius B in x ray 6 October 2000 Sirius Matters Alien Contact Chandra X ray Center 28 November 2000 Retrieved 21 March 2021 Sankey John Getting Sirius About Time www johnsankey ca Retrieved 21 March 2021 Barker Tho Stukeley W 1760 Remarks on the Mutations of the Stars Philosophical Transactions 51 498 504 doi 10 1098 rstl 1759 0049 JSTOR 105393 Portals Stars Outer space Astronomy 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