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R136a1

 Observation data Characteristics Epoch J2000.0      Equinox J2000.0 Artist's impression of Wolf-Rayet star R136a1 in the Large Magellanic Cloud. Constellation Dorado Right ascension 5h 38m 42.43s[1] Declination −69° 06′ 02.2″[1] Apparent magnitude(V) 12.77[1] Spectral type B−V color index +0.01[1] Distance 165,000 ly Mass 265+80 −35[2]320 birth massM☉ Radius 35.4+4.0 −3.6[2] R☉ Luminosity ≈ (8.7)×106[2] L☉ Temperature 53,000 ± 3,000[2] K Age unknown years BAT99 108, RMC 136a1, [HSH95] 3, [WO84] 1b, Cl* NGC 2070 MH 498, [CHH92] 1, [P93] 954. SIMBAD data

R136a1 is a blue hypergiant star, currently on record as the most massive star known, at an estimated 265 solar masses.[2] The star also holds the record for the most luminous at 8,700,000 times the luminosity of the Sun.[2] It is a member of R136, asuper star cluster near the center of the 30 Doradus complex (also known as theTarantula Nebula), in the Large Magellanic Cloud. The mass of the star was determined by Paul Crowther et al. (2010).[2]

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## Discovery

News of the star's discovery was published in July 2010. A team of British astronomers led by Paul Crowther, professor of astrophysics at the University of Sheffield, usedEuropean Southern Observatory's Very Large Telescope (VLT) in Chile, as well as data from the Hubble Space Telescope, to study two star clustersNGC 3603 and R136a.[2][3]R136a was once thought to be a supermassive object with             1000–3000       solar masses. R136a's nature was resolved by holographic speckle interferometry and found to be a dense star cluster.[4] The team found several stars with surface temperatures exceeding 40,000- 56,000 K, more than seven times that of the Sun, and which are several million times brighter. At least three of the stars weigh in at about 150 solar masses.

## Physical characteristics

Left to right: a red dwarf, the Sun, a blue dwarf, and R136a1. R136a1 is not the largest known star in terms of volume; this distinction belongs to VY Canis Majoris.

R136a1 is a Wolf–Rayet star with surface temperature over 50,000 K.[2] Like other stars that are close to the Eddington limit, R136a1 has been shedding a large fraction of its initial mass through a continuous stellar wind. It is estimated that, at its birth, the star held 320 solar masses and has lost 50 solar masses over the past million years.[2]

Stars between about 8 and 150 solar masses explode at the end of their lives assupernovae, leaving behind neutron stars orblack holes. Having established the existence of stars between 150 and 300 solar masses, astronomers suspect that such an enormous star will perish as a hypernova, a stellar explosion with an energy of over 100 supernovae (1046 joules). The star may also die prematurely long before its core could collapse naturally from lack of fuel as a "pair instability supernova". Hydrogen-fusing cores should create large numbers of electronpositron pairs, which drop the thermal pressure present within the star to the point a partial collapse occurs. If R136a1 underwent such an explosion it would fail to leave behind a black hole and instead the dozen solar masses of iron within its core would be blown out into the interstellar medium as a supernova remnant.[3]

## References

1. a b c d RMC 136a1 – Star in Cluster, database entry, SIMBAD.
2. a b c d e f g h i j k Crowther, Paul A.; Schnurr, Olivier; Hirschi, Raphael; Yusof, Norhasliza; Parker, Richard J.; Goodwin, Simon P.; Kassim, Hasan Abu (2010). "The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 M stellar mass limit". Monthly Notices of the Royal Astronomical Society 408 (2): 731–751. Bibcode 2010MNRAS.408..731Cdoi:10.1111/j.1365-2966.2010.17167.xarXiv:1007.3284.
3. a b "A 300 Solar Mass Star Uncovered"ESO Press Release. 2010-07-21.
4. ^ http://www.eso.org/sci/publications/messenger/archive/no.40-jun85/messenger-no40-4-6.pdfPDF (R136a and the Central Object in the Giant HII Region NGC 3603 Resolved by Holographic Speckle Interferometry).

# Pistol Star

(Redirected from The Pistol Star)
 Observation data Characteristics Epoch J2000 Equinox J2000 False-color image of the Pistol Star and Pistol Nebula, taken by HST NICMOS. Constellation Sagittarius Right ascension 17h 46m 15.3s Declination −28° 50′ 04″ Apparent magnitude (V) invisible (4) Spectral type B Variable type Luminous blue variable Mass 80–150 M☉ Radius 300–340 R☉ Luminosity > 106 L☉ Temperature 14–21,000 K Age ≈2×106 years

The Pistol Star[1] is a blue hypergiant and is one of the most luminous known stars in the Milky Way Galaxy. It is one of many massive young stars in the Quintuplet cluster in the Galactic Center region. The star owes its name to the shape of the Pistol Nebula, which it illuminates. It is located approximately 25,000 light years from Earth in the direction of Sagittarius. It would be visible to the naked eye as a fourth magnitude star, if it were not for the interstellar dust that completely hides it from view in visible light.

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##  Properties

The Pistol Star was discovered by the Hubble Space Telescope in the early 1990s. The star is thought to have ejected almost 10 solar masses of material in giant outbursts perhaps 4,000 to 6,000 years ago (as observed from Earth). Its stellar wind is over 10 billion times stronger than the Sun's. Its exact age and future are not known, but it is expected to end in a brilliant supernova or hypernova in 1 to 3 million years. Some astronomers conjecture that its large mass may be related to its location near the Galactic Center, since the star formation process there may favor massive objects. Early reports suggested that it might be the most luminous star known, producing almost 100 million times as much power as the Sun. Later studies, however, have reduced its estimated luminosity to roughly 4 million times that of the Sun, making it a luminous blue variable about one-third as luminous as the binary star system Eta Carinae.[2] Even so, it radiates about as much energy in 20 seconds as does the Sun in a year.

##  Luminous stars

Objects in this class have 80 to 150 times the mass of the Sun and lifetimes of only a few million years. Unlike ordinary stars, they are strongly affected by the outward pressure of the light that they emit, which blows off massive winds from their outer atmospheres. Besides the Pistol Star, several other objects have been cited as the "most luminous star" in recent years. Almost all of them have been demoted by later, improved studies. Among the most famous is Eta Carinae, now confirmed to be a system of at least two stars. Our galaxy probably has 10 to 100 stars surpassing Eta Carinae, but their visible light is hidden by interstellar dust, hindering their immediate identification and detailed study. Most should eventually be observable in infrared light.

##  References

1. ^ Najarro, F. (2005). "The Fate of the Most Massive Stars". ASP Conference 332. pp. 58–68.

# Carina Nebula

Carina Nebula

An image of NGC 3372 taken with an amateur telescope
Credit: HST/NASA/ESA
Observation data: J2000.0 epoch
Type Emission
Right ascension 10h 45m 08.5s[1]
Declination -59° 52′ 04″[1]
Distance ~6500-10000 ly [1]
+1.0
Constellation Carina
Physical characteristics
~10.8
Notable features Includes dark nebula
Keyhole Nebula
Other designations NGC 3372,[2] ESO 128-EN013,[1] GC 2197[1]
v · d · e

The Carina Nebula. Credit ESO
The Carina Nebula around the Wolf–Rayet star WR 22. Credit ESO

The Carina Nebula (also known as the Great Nebula in Carina, the Eta Carina Nebula, or NGC 3372) is a large bright nebula that surrounds several open clusters of stars. Eta Carinae and HD 93129A, two of the most massive and luminous stars in our Milky Way galaxy, are among them. The nebula lies at an estimated distance between 6,500 and 10,000 light years from Earth. It is located in the constellation of Carina. The nebula contains multiple O-type stars.

The nebula is one of the largest diffuse nebulae in our skies. Although it is some four times as large and even brighter than the famous Orion Nebula, the Carina Nebula is much less well known, due to its location far in the Southern Hemisphere. It was discovered by Nicolas Louis de Lacaille in 1751–52 from the Cape of Good Hope.

Within the large bright nebula is a much smaller feature, immediately surrounding Eta Carinae itself. This small nebula is known as the Homunculus Nebula (from the Latin meaning Little Man), and is believed to have been ejected in an enormous outburst in 1841 which briefly made Eta Carinae the second-brightest star in the sky.

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##  Objects within the Carina Nebula

A Hubble Space Telescope (HST) false-color image/diagram of the of Carina Nebula (Zoomable version); Credit: HST/NASA/ESA
Carina Nebula (high resolution)

###  Eta Carinae

Eta Carinae is a highly luminous hypergiant star. Estimates of its mass range from 100 to 150 times the mass of the Sun, and its luminosity is about four million times that of the Sun.

This object is currently the most massive star that can be studied in great detail. Several other known stars may be more luminous and more massive, but data on them is far less robust. (Caveat: Since examples such as the Pistol Star have been demoted by improved data, one should be skeptical of most available lists of "most massive stars." In 2006, Eta Carinae still had the highest confirmed luminosity, based on data across a broad range of wavelengths.) Stars with more than 80 times the mass of the Sun produce more than a million times as much light as the Sun. They are quite rare—only a few dozen in a galaxy as big as ours—and they flirt with disaster near the Eddington limit, i.e., the outward pressure of their radiation is almost strong enough to counteract gravity. Stars that are more than 120 solar masses exceed the theoretical Eddington limit, and their gravity is barely strong enough to hold in its radiation and gas, resulting in a possible supernova or hypernova in the near future.

Eta Carinae's effects on the nebula can be seen directly. The dark globules in the above image and some other less visible objects have tails pointing directly away from the massive star. The entire nebula would have looked very different before the Great Eruption in the 1840s surrounded Eta Carinae with dust, drastically reducing the amount of ultraviolet light it put into the nebula.

###  Keyhole Nebula

A portion of the Carina Nebula is known as the Keyhole Nebula, a name given to it by John Herschel in the 19th century. The Keyhole Nebula is actually a much smaller and darker cloud of cold molecules and dust, containing bright filaments of hot, fluorescing gas, silhouetted against the much brighter background nebula. The diameter of the Keyhole structure is approximately 7 light years.

##  References

1. ^ a b c d e "Object Data - NGC 3372". Results for NGC 3372. Retrieved 2008-04-25.
2. ^ "SIMBAD Astronomical Database". Results for NGC 3372. Retrieved 2007-04-26.

# Sirius

 Observation data Characteristics Epoch J2000.0 Equinox J2000.0 (ICRS) The position of Sirius. Constellation Canis Major Pronunciation Right ascension 06h 45m 08.9173s[2][note 1] Declination −16° 42′ 58.017″[2][note 1] Apparent magnitude (V) −1.46 (A)[2] / 8.30 (B)[3] Spectral type A1V (A)[2] / DA2 (B)[3] U−B color index −0.05 (A)[4] / −1.04 (B)[3] B−V color index 0.01 (A)[2] / −0.03 (B)[3] Radial velocity (Rv) −7.6[2] km/s Proper motion (μ) RA: −546.05[2][note 1] mas/yr Dec.: −1223.14[2][note 1] mas/yr Parallax (π) 379.21 ± 1.58[2] mas Distance 8.6 ± 0.04 ly (2.64 ± 0.01 pc) Absolute magnitude (MV) 1.42 (A)[note 2] / 11.18 (B)[3] Companion α CMa B Period (P) 50.090 ± 0.055 yr Semimajor axis (a) 7.50 ± 0.04" Eccentricity (e) 0.5923 ± 0.0019 Inclination (i) 136.53 ± 0.43° Longitude of the node (Ω) 44.57 ± 0.44° Periastron epoch (T) 1894.130 ± 0.015 Argument of periastron (ω) (secondary) 147.27 ± 0.54° Mass 2.02[6] (A) / 0.978[6] (B) M☉ Radius 1.711[6] (A) / 0.0084 ± 3%[7] (B) R☉ Surface gravity (log g) 4.33[8] (A)/8.57[7] (B) Luminosity 25.4[6] (A) / Temperature 9,940[8] (A) / 25,200[6] (B) K Metallicity [Fe/H] =0.50[9] (A) Rotation 16 km/s[10] (A) Age 2–3 × 108[6] years System: Dog Star, Aschere, Canicula, Al Shira, Sothis,[11] Mrgavyadha, Lubdhaka,[12] Tenrōsei,[13] 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.[2][14][15]

Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek Σείριος Seirios ("glowing" or "scorcher"). The star has the Bayer designation Alpha Canis Majoris (α CMa). What the naked eye perceives as a single star 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. The distance separating Sirius A from its companion varies between 8.1 and 31.5 AU.[16]

Sirius appears bright because of both its intrinsic luminosity and its proximity to Earth. At a distance of 2.6 parsecs (8.6 ly), the Sirius system is one of Earth's near neighbors. 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[6] 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.[6] 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.[6]

Sirius is also known colloquially as the "Dog Star", reflecting its prominence in its constellation, Canis Major (Greater Dog).[11] 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.

##  Observational history

Sirius/Sopdet

Sirius, known in ancient Egypt as Sopdet (Greek: Sothis), is recorded in the earliest astronomical records. 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 through the duat (Egyptian underworld).[18]

The ancient Greeks observed that the appearance of Sirius heralded the hot and dry summer, and feared that it caused plants to wilt, men to weaken, and women to 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 malignant 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 3rd century BC feature dogs or stars with emanating rays, highlighting Sirius' importance.[20] 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.[22]

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. He curiously depicted it as one of six red-coloured stars (see the Red controversy section below). The other five are class M and K stars, such as Arcturus and Betelgeuse.[23]

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 archipelago of Fiji at 17°S and thus passes directly over the islands each night.[24] 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.[25] 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.[26]

###  Kinematics

In 1718, Edmond Halley discovered the proper motion of the hitherto presumed "fixed" stars[27] after comparing contemporary astrometric measurements with those given in Ptolemy's Almagest. The bright stars Aldebaran, Arcturus and Sirius were noted to have moved significantly, the last of which having progressed 30 arc minutes (about the diameter of the moon) southwards in 1,800 years.[28]

In 1868, Sirius became the first star to have its velocity measured. Sir William Huggins examined the spectrum of this star and observed a noticeable red shift. He concluded that Sirius was receding from the Solar System at about 40 km/s.[29][30] Compared to the modern value of −7.6 km/s,[2] this both was an overestimate and had the wrong sign; the minus means it is approaching the Sun. However, it is notable for introducing the study of celestial radial velocities.

###  Discovery of a companion

A simulated image of Sirius A and B using Celestia

In 1844 German astronomer Friedrich Bessel deduced from changes in the proper motion of Sirius that it had an unseen companion.[31] 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".[32] This happened during testing of a 18.5-inch (470 mm) aperture great refractor telescope for Dearborn Observatory, which was the largest refracting telescope lens in existence at the time, and the largest telescope in America.[33]

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.[34] 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 confirmed as a background object.[35]

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.[36] This led astronomers to conclude that it was a white dwarf, the second to be discovered.[37] 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.[38] 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.[39][40][41][42]

###  Red controversy

Around 150 AD, the Hellenistic astronomer Claudius 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.[43] 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.[44] 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.[45] Thomas Jefferson Jackson See resurrected discussion on red Sirius with the publication of several papers in 1892, and a final summary in 1926.[46] 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.[47] Seneca, too, had described Sirius as being of a deeper red colour than Mars.[48] 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.[49] 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.[50][51]

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.[52] However, other scholars replied that it was likely St. Gregory had been referring to Arcturus instead.[53][54]

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.[48] An interaction with a third star, to date undiscovered, has also been proposed as a possibility for a red appearance.[55] 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.[48]

##  Visibility

The image of Sirius A and Sirius B taken by the Hubble Space Telescope. The white dwarf can be seen to the lower left.[56] The diffraction spikes and concentric rings are instrumental effects.

With an apparent magnitude of −1.46, Sirius is the brightest star in the night sky, almost twice the brightness of the second brightest star, Canopus.[57] However, it is not as bright as the Moon, Venus, or Jupiter. At times, Mercury and Mars are also brighter than Sirius.[58] Sirius can be seen from almost every inhabited region of the Earth's surface, with only those 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.[59] Sirius, along with Procyon and Betelgeuse, forms one of the three vertices of the Winter Triangle to observers in the Northern Hemisphere.[60] Due to its declination of roughly −17°,[2] 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.[61]

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.[62] These observing conditions are more easily met in the southern hemisphere, due to the southerly declination of Sirius.

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. A periastron occurred in 1994[note 4] and the pair have since been moving apart, making them easier to separate with a telescope.[63]

At a distance of 2.6 parsecs (8.6 ly), the Sirius system contains two of the eight nearest stars to the Solar System[64] and is the fifth closest stellar system to ours.[64] 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.[65] However, it is still around 25 times more luminous than the Sun.[6] The closest large neighbouring star to Sirius is Procyon, 1.61 parsecs (5.24 ly) away.[66] 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 (1.3 pc) of Sirius in approximately 296,000 years.[67]

##  System

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 astronomical units (3.0×109 km; 1.9×109 mi)[note 5] (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 A1V, with an estimated surface temperature of 9,940 K.[8] 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.[66][69] The Chandra X-ray Observatory image shows Sirius B outshining its bright partner as it is a brighter X-ray source.[70]

###  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 double that of the Sun.[6][71] 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,[10] which does not produce any significant flattening of its disk.[72] 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.[73] A weak magnetic field has been detected on the surface of Sirius A.[74]

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.[72] 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.

Sirius A is classed as an Am star because the spectrum shows deep metallic absorption lines,[75] indicating an enhancement in elements heavier than helium, such as iron.[66][72] When compared to the Sun, the proportion of iron in the atmosphere of Sirius A relative to hydrogen is given by $\begin{smallmatrix}[\frac{Fe}{H}]=0.5\end{smallmatrix}$,[9] which is equivalent to 100.5, 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.[72]

###  Sirius B

The orbit of Sirius B around A as seen from Earth (slanted ellipse) and as seen face-on (wide horizontal ellipse).

With a mass nearly equal to the Sun's, Sirius B is one of the more massive white dwarfs known (0.98 solar mass[76]); 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.[76] The current surface temperature is 25,200 K.[6] 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.[77]

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, around 120 million years ago. The original star had an estimated 5 solar masses[6] and was a B-type star (roughly B4-5)[78][79] 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.

This star is primarily composed of a carbon-oxygen mixture that was generated by helium fusion in the progenitor star.[6] This is overlaid by an envelope of lighter elements, with the materials segregated by mass because of the high surface gravity.[80] 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.[81]

###  Sirius star cluster

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.[82] 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.[6][83][84] 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.[85] This is 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.[86]

##  Etymology and cultural significance

The most commonly used proper name of this star comes from the Latin Sīrius, from the Ancient Greek Σείριος (Seirios, "glowing" or "scorcher"),[87] although the Greek word itself may have been imported from elsewhere before the Archaic period,[88] one authority suggesting a link with the Egyptian god Osiris.[89] The name's earliest recorded use dates from the 7th century BC in Hesiod's poetic work Works and Days.[88] Sirius has over 50 other designations and names attached to it.[57] In Arabic it is known as الشِّعْرَى (transliteration: aš-ši‘rā or ash-shira; the leader),[90] 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).[91][92] In Scandinavia, the star has been known as Lokabrenna ("burning done by Loki", or "Loki's torch").[93] In the astrology of the Middle Ages, Sirius was a Behenian fixed star,[94] associated with beryl and juniper. Its astrological symbol was listed by Heinrich Cornelius Agrippa.[95]

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.

This name may derive from the Egyptian god Anubis. The Gaza Sphinx, which Robert Temple in his book "The Sphinx Mystery" has documented is actually a dog and not a lion, had originally the head of Anubis. Anubis was a dog and not a jackal as there were no jackals in Egypt at that time. The Sphinx is facing Sirius at the time when the star rises over the horizon at sunrise at the summer solstice, the time when the Nile started flooding, and the Egyptians probably held great ceremonies when that happened.[citation needed]

It 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 whom they had bitten.[20] Homer, in the Iliad, describes the approach of Achilles toward Troy in these words:

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.[96]

In Chinese astronomy the star is known as the star of the "celestial wolf" (Chinese and Japanese: 天狼; ; Chinese romanization: Tiānláng; Japanese romanization: Tenrō;[97] in the Mansion of Jǐng (井宿). Farther afield, many nations among the indigenous peoples of North America also associated Sirius with canines; the Seri and Tohono O'odham 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".[98]

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.[99]

Sirius is mentioned in Surah 53, An-Najm ("The Star"), of the Qur'an, where it is given the name الشِّعْرَى (al-shiʿraa.) The verse is: "وأنَّهُ هُوَ رَبُّ الشِّعْرَى", "That He is the Lord of Sirius (the Mighty Star)." (53:49)[100]

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.[101]

###  Dogon

The Dogon people are an ethnic group in Mali, West Africa, reported to have traditional astronomical knowledge about Sirius that would normally be considered impossible without the use of telescopes. According to Marcel Griaule's books Conversations with Ogotemmêli and The Pale Fox they knew about the fifty-year orbital period of Sirius and its companion prior to western astronomers. They also refer to a third star accompanying Sirius A and B. Robert Temple's 1976 book The Sirius Mystery, credits them with knowledge of the four Galilean moons of Jupiter and the rings of Saturn. This has been the subject of controversy and speculation. According to a 1978 Skeptical Inquirer article it is possibly the result of cultural contamination.[102] Some have suggested the contaminators to have been the ethnographers themselves.[103][104] Others see this explanation as being too simplistic.[105]

###  Modern legacy

Sirius is frequently a subject used in science fiction and related popular culture,[106] and even the subject of poetry.[107] It is featured on the coat of arms of Macquarie University, and is the name of its alumnae journal.[108] The name of the North American satellite radio company, Satellite CD Radio, Inc., was changed to Sirius Satellite Radio in November 1999, being named after "the brightest star in the night sky".[109] Composer Karlheinz Stockhausen has been claimed to have said on several occasions that he came from a planet in the Sirius system.[110][111] Astronomer Noah Brosch has speculated that the name of the character Sirius Black from the Harry Potter stories might have been inspired by "Sirius B", and notes that the wizard has the ability to transform into a dog.[107] In the BBC Doctor Who series, the Doctor reveals the star actually consists of two smaller ones.

Sirius is one of the 27 stars on the flag of Brazil, where it represents the state of Mato Grosso.[112]

Seven ships of Great Britain's 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.[113] The Royal Australian Navy subsequently named a vessel HMAS Sirius in honor of the flagship.[114] American vessels include the USNS Sirius as well as a monoplane model—the Lockheed Sirius, the first of which was flown by Charles Lindbergh.[115] The name was also adopted by Mitsubishi Motors as the Mitsubishi Sirius engine in 1980.[116]

##  Notes

1. ^ a b c d Astrometric data, mirrored by SIMBAD from the Hipparcos catalogue, pertains to the center of mass of the Sirius system. See §2.3.4, Volume 1, The Hipparcos and Tycho Catalogues, European Space Agency, 1997, and the entry for Sirius in the Hipparcos catalogue (CDS ID I/239.)
2. ^ For apparent magnitude m and parallax π, the absolute magnitude Mv of Sirius A is given by:
$\begin{smallmatrix}M_v\ =\ m + 5 (\log_{10} {\pi} + 1)\ =\ -1.47 + 5 (\log_{10}{0.37921} + 1)\ =\ 1.42\end{smallmatrix}$
See: Tayler, Roger John (1994). The Stars: Their Structure and Evolution. Cambridge University Press. p. 16. ISBN 0-521-45885-4.
3. ^ Bolometric luminosity of Sirius B calculated from L=4πR2σTeff4. (This simplifies to Ls=(Rs)^2*(Ts)^4, where Ls, Rs and Ts are Luminosity, Radius and Temperature all relative to solar values) See: Tayler, Roger John (1994). The Stars: Their Structure and Evolution. Cambridge University Press. p. 16. ISBN 0-521-45885-4.
4. ^ Two full 50.09-year orbits following the periastron epoch of 1894.13 gives a date of 1994.31.
5. ^ 1 light year = 63,241 AU; semi-major axis = distance × tan(subtended angle) = 8.6 × 63,241 × tan(7.56″) = 19.9 A.U., approximately

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###  Cited texts

• Brosch, Noah (2008). Sirius Matters. Springer. ISBN 1-4020-8318-1
• Holberg, J.B. (2007). Sirius: Brightest Diamond in the Night Sky. Chichester, UK: Praxis Publishing. ISBN 0-387-48941-X

# Alcyone (star)

 Observation data Characteristics Epoch J2000 Equinox J2000 Alcyone is the bright star at the center of the map. Constellation Taurus Right ascension 03h 47m 29.0765s[1] Declination 24° 06′ 18.494″[1] Apparent magnitude (V) 2.873[1] Spectral type B7IIIe[2] U−B color index -0.35[3] B−V color index -0.09[3] Variable type suspected Radial velocity (Rv) 10.1[1] km/s Proper motion (μ) RA: 19.35[1] mas/yr Dec.: -43.11[1] mas/yr Parallax (π) 8.87 ± 0.99[4] mas Distance approx. 370 ly (approx. 110 pc) Absolute magnitude (MV) -2.39 Mass Radius ~10[5] R☉ Luminosity 2,400[5] L☉ Temperature 13,000[5] K Rotation 215 km/s[2] η Tau, 25 Tau, HR 1165, HD 23630, BD+23 541, FK5 139, HIP 17702, SAO 76199, GC 4541, BDS 1875, CCDM 03474+2407 SIMBAD data

Alcyone (η Tau, η Tauri, Eta Tauri) is a star system in the constellation Taurus. It is the brightest star in the Pleiades open cluster, which is a young cluster, aged at less than 50 million years. Alcyone is approximately 370 light years from Earth. It is named after the mythological figure Alcyone, one of the mythological Pleiades. It is known as 昴宿六 (the Sixth Star of the Hairy Head) in Chinese.

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##  Overview

The main star, known as Alcyone A, is a blue-white B-type giant similar to many of the other B-type stars in the Pleiades cluster. It has an apparent magnitude of +2.87 (absolute magnitude = −2.39), and a radius almost 10 times that of the Sun.[5] Its temperature is approximately 13,000 K giving it a total luminosity that is 2,400 times solar. The spectral type of B7IIIe indicates that emission lines are present in its spectrum. Like many Be stars, Alcyone A has a high rotational velocity of 215 km/s,[2] which has created a gaseous disk flung into orbit around the star from its equator.

##  Star System

Alcyone is an eclipsing binary, and the two components have a separation of 0.031 arcseconds, or about the distance from the Sun to Jupiter.

The binary star is orbited by three companions. Alcyone B and Alcyone C are both 8th magnitude white A-type dwarfs and are separated from A by 117 and 181 arcseconds respectively. Alcyone D is a yellow-white F-type dwarf, 191 arcseconds from the primary. It has an apparent magnitude of +8.7. Alcyone C is classified as a Delta Scuti type variable star and its brightness varies from magnitude +8.25 to +8.30 over 1.13 hours.

##  References

1. ^ a b c d e f "SIMBAD query result: ALCYONE -- Be Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-06-30.
2. ^ a b Johnson, H. L.; Iriarte, B.; Mitchell, R. I.; Wisniewski, W. Z. (1966). "UBVRIJKL photometry of the bright stars." (PDF). Comm. Lunar Plan. Lab., 4. Bibcode 1966CoLPL...4...99J.
3. ^ Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E. et al (1997). "The HIPPARCOS Catalogue" (PDF). Astronomy and Astrophysics 323: L49–L52. Bibcode 1997A&A...323L..49P.
4. ^ a b c d e Professor James B. (Jim) Kaler. "ALCYONE (Eta Tauri)". University of Illinois. Retrieved 2010-06-30.

Mandalas

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Historically mandalas have more than 5000 years of existence and they are conceived for rituals and  healing.

Mandalas  are discovered in all, planets, lands, stars, Celtic, Mayan, Aztec, Navajo, hopies, symbols…  the cloverleaves of the medieval Gothic cathedrals.

Also mandalas are present in the nature in a three-dimensional way,  in the shape of cells, molecules of water, the snowflakes, the spider webs, the flowers...

The two-dimensional or three-dimensional representation of the mandalas it is not limited and they are interpreted like a model of interdimensional and multidimensional universe.

All in the universe is energy and we can agree it if we tune in, we echo and we vibrate with it, creating.

Mandalas transcend time, space and matter and puts us in contact with the inherent energy that there is in it.

Visit the gallery of mandalas!

Mandalas by its forms and colors influences positively in the personal knowledge.

Qúé es Mandala

Históricamente los mandalas tienen algunos más de 5000 años y se conciben como ritual e instrumento de sanación.

Los mandalas se descubren en todo,  en el planeta tierra, los astros, símbolos celtas o amerindios, mayas, aztecas, navajos, hopies, etc, hasta los rosetones de las catedrales góticas medievales.

También el mandala está presente en la naturaleza de manera tridimensional, ya sea en forma de células, moléculas de agua, los copos de nieve, las telas de araña, las flores...

La representación bidimensional o tridimensional del mandala no se limita y se interpretan como un modelo interdimensional y multidimensional.

Todo en el universo es energía y podemos acceder a ella si nos sintonizamos,

resonamos y vibramos con ella, manifestando y creando.

El mandala trasciende el tiempo el espacio y la materia y nos pone en contacto con la energía inherente que hay en él.

!Visite la galería de imágenes de mandalas!

El mandala por su composición de formas y colores influye positivamente en el conocimiento personal.

Mandalas

Historically mandalas have more than 5000 years of existence and they are conceived for rituals and  healing.

Mandalas  are discovered in all, planets, lands, stars, Celtic, Mayan, Aztec, Navajo, hopies, symbols…  the cloverleaves of the medieval Gothic cathedrals.

Also mandalas are present in the nature in a three-dimensional way,  in the shape of cells, molecules of water, the snowflakes, the spider webs, the flowers...

The two-dimensional or three-dimensional representation of the mandalas it is not limited and they are interpreted like a model of interdimensional and multidimensional universe.

All in the universe is energy and we can agree it if we tune in, we echo and we vibrate with it, creating.

Mandalas transcend time, space and   matter and puts us in contact with the inherent energy that there is in it.

Visit the gallery of mandalas!

Mandalas by its forms and colors influences positively in the personal knowledge.

## NEOREIKI está dedicado a impartir enseñanzas espirituales de miles de años de antiguedad con las nuevas de la actualidad, sin dar un curso de los acontecimientos y sí el apoyo en tu progreso.

NEOREIKI is dedicated to educating thousands of years of old spiritual in heritage with the new ones of today, without giving a course of events and supported in your progress.