Sirius
Sirius, or Sirius in its Latin name, is the proper name of the star Alpha Canis Maioris (α CMa, also Alpha Canis Majoris), the brightest in the entire night sky as seen from Earth, located in the southern celestial hemisphere constellation Canis Maior. This remarkable star, which is actually a binary star, has been well known since ancient times; for example, in Ancient Egypt, the heliacal rise of Sirius marked the time of the Nile floods, and it has been present in civilizations as diverse as the Greek, Mayan, and Polynesian. Sometimes, and colloquially, Sirius is called "Dog Star" as a result of the constellation to which it belongs.
The primary component of the two stars that make up the system, Sirius A, is a white main-sequence star of spectral type A1V with a surface temperature of 9,726 °C (10,000 K) and is distant to about 8.6 light-years from the solar system, making it the seventh closest star to the Sun. Its apparent magnitude in the B band (blue) is –1.46, and in the V band it is –1.47 Friedrich Bessel, in 1844, deduced the presence of a companion, a very faint celestial object now called Sirius B or "the Pup", which was first observed incidentally in 1862 by the astronomical objective builder Alvan Graham Clark. It was one of the first white dwarfs to be discovered, its magnitude in the V band is 8.44, its spectral type is DA2, and its surface temperature is about 25,200 K.
Due to certain irregularities in the orbit of the Sirius system formed by both stars, the presence of a third star, Sirius C, has been suggested, a presumed red dwarf with a fifth of the mass of the Sun and spectral type M5-9, in a six-year elliptical orbit around Sirius A. This object has not yet been observed and its actual existence is disputed.
Etymology and names
The most common proper name for this star comes from the Latin Sīriŭs, in turn from the ancient Greek Σείριος (Seirios), although the word Hellene may have been imported from elsewhere prior to Archaic Ancient Greece, with some suggesting a connection to the Egyptian god Osiris. The first documented use of this name dates from the 7th century BCE. C., in the poetic work Works and days, by Hesiod, who described Sirius by its scintillation saying, for example, ποίκιλος Σείριος: poíkilos Seirios, "Sirius, the one who shines in many colors". However, Sirius has more than fifty different designations.
In Arabic the star is known as الشِّعْرَى (transliterated: aš-ši'rā or ash-shira; the leader), from which the alternative Aschere. In Sanskrit it is called Mrgavyadha, "deer hunter", or Lubdhaka, "hunter". Under the first of these two names, Sirius represents Rudra (Shiva). Traveling far north, in Scandinavia the star was called Lokabrenna, something like "Loki's torch". During the Middle Ages, in astrology Sirius was one of the fifteen behenian fixed stars, associated specifically with beryl and junipers, and whose astrological symbol was listed by Agrippa of Nettesheim.
Historically, many cultures have assigned a special importance to Sirius, which in particular has been frequently associated with dogs, hence it is colloquially known as the "Dog Star" (and all its idiomatic variants: Dog Star , Stella del Cane, Hundsstern, Köpek-yıldız, Hundstjärnan, etc.), which which has to do in part with the fact that the names of the constellations are already old and also with the fact that it is the brightest star in its constellation, Canis Maior, the "Great Dog", which has typically been identified as the dog of the giant Orion, although this has not been the only option. Even Homer, in his Iliad, described Achilles' approach to Troy by referring to Sirius as Orion's dog, as the brightest star and as evil.
In Chinese astronomy, it is known as the "heavenly wolf" star (in Chinese and Japanese, 天狼; pinyin: Tiānláng; rōmaji: Tenrō) in Jǐng's Mansion (井宿). On the other hand, in North America, many indigenous peoples similarly related Sirius to canids; The Seri and Tohono O'odham took the star to be a dog chasing sheep from the mountains, while the Blackfeet called it "Dog-Face." The Cherokee people paired Sirius with Antares as a pair of watchdogs guarding each side of the "Path of Souls"; the Pawnee of Nebraska made several associations: the Skidi tribe named it "Wolf Star", but others used the variant "Coyote Star". In Alaska, the Inuit of the Bering Strait knew Sirius as "Moon Dog".
In contrast, various cultures have linked Sirius with bows and arrows. The ancient Chinese envisioned a great bow and arrow formed by Puppis and Canis Maior streaking across the southern sky, so that the tip of the arrow points to the Syrian wolf. A similar connection is found in the temple of Hathor at Dendera, where the goddess Satis shoots her arrow at Hathor—Sirius, who under the name Tir was portrayed as the arrow itself in Persian culture. later-.
Sirius is also mentioned in the 53rd chapter of the Qur'an, titled An-Najm, “The Star”, as follows: وأنَّهُ هُوَ رَبُّ الشِّعْرَى, “That He is the Lord of Sirius (the Mighty Star)" (53:49).
Although it is true that Sirius is designated by many different scientific names, the vast majority of them are made up of initials and a number. The classic naming of Bayer, from the 17th century, based on ordering the stars of each constellation by apparent brightness using the Greek alphabet followed by the Latin name of the constellation in genitive, assigned to this star the name Alpha Canis Maioris or α Canis Maioris, abbreviated as αCMa. The drawback of this system lay in the fact that there are many more stars per constellation than letters in the alphabet, so John Flamsteed proposed a new method consisting of giving each star in a constellation a number and not a letter, following the ascension crescent line instead of gloss. Thus, and also adding the Latin genitive, Sirius remained as 9 Canis Maioris, abbreviated in turn 9 CMa. Later, more extensive and precise stellar catalogs have been created. In the Bonner Durchmusterung, after the corresponding acronyms of the catalog (there are several due to their enlargements) are the declination of the star and a number, Sirius is BD −16° 1591. In Henry Draper's, which takes into account the order of right ascension for the epoch 1900.0 and which was the first attempt to classify by spectral type, Sirius was assigned HD 48915; but in the Bright Star Catalogue, which lists roughly the stars visible to the naked eye, Sirius happens to be HR 2491. Many others are PPM 217626, from the Positions and Proper Motions Catalogue, SAO 151881, from the Smithsonian Astrophysical Observatory, GC 8833, from the Boss General Catalogue, WDS 06451-1643A, ADS 5423, GL 244, FK5 257, LHS 219, NSV 17173 and that of the recent, precise and complete Hipparcos catalogue: HIP 32349.
Historical and cultural observation
As an exceptionally colorful star, Sirius has been present since prehistoric times in the mythology, religions, and customs of many cultures.
Jeoglyphic |
Sirius, a star known in Ancient Egypt as Sopdet, Sothis or Sethis (in Greek, Σῶθις, Sothis), appears already in the first astronomical records, already symbolized by a dog, origin of the later name of the Canis Major. During the time of the Middle Kingdom of Egypt, the The Egyptian people based their calendar on the heliacal rising of Sirius, that is, the first day it becomes visible to the West in the early morning just before sunrise, after having moved sufficiently far from the Sun's brightness. The importance of this The fact is that it marked the beginning of the annual flood season of the Nile River, before the summer solstice, after a seventy-day absence from the night skies. The Sothis hieroglyph shows a five-pointed star and a triangle. Sothis was identified with the great goddess Isis, who was part, together with her husband Osiris and her son Horus, of a tritheism, while that period of seventy days in which Sirius was not seen in the sky symbolized the passage of Isis and Osiris through the duat, the Egyptian underworld. Similarly, for the Chibchas of present-day Colombia, the heliacal rise of Sirius heralded the beginning of the rainy season.
The inescapable relationship between Sirius and the Egyptian calendar has meant that, over time, Sirius and the sothiac cycle (also sotiaco, sothiaco or sótico) have also become an important element that helps to determine with greater accuracy Ancient Egyptian chronology, since the ancient Egyptians did not use a single system for dating. On the other hand, this method is not exempt from drawbacks and this has led to the appearance of some detractors who prefer to resort to other systems. The Sothian cycle is the period of 1461 years of 365 exact days (of the Egyptian calendar, in the Julian they 1460 years of 365.25 days) that it takes for the heliacal rise of Sirius to coincide again with the beginning of the new year, the first day of the month Thoth, a lack of coordination that is caused because the Egyptian year did not coincide with the sidereal one. Thanks to the conservation of some archaeological remains that refer to the heliacal rise of Sirius and of which it is known to which dynasty they belong, such as an ivory tablet of Pharaoh Dyer, a reference can be set from which to date the events that occurred. in Ancient Egypt.
In Sumer, around the 3rd millennium BC, Sirius already took central roles in Sumerian religion. As a reference star for the calendar, and under the name MULKAK.SI.SÁ, it played an important role in the agricultural cycle; and with the name of MULKAK.TAG.GA (arrow of the sky) Sirius was considered as a main divinity but subordinate to the "dominant star of God over the rest of celestial objects', Venus, who was worshiped as the goddess Inanna. Finally, in the procession of Akitu —new year— Sirius received its corresponding offerings. Later, and practically without changes in what it represented, for the Assyrians and Babylonians Sirius also meant, according to the clay tablets MUL. APIN, the signal to specify leap years.
The Ancient Greek civilization observed that the appearance of Sirius heralded the hot and dry Mediterranean summers, and therefore feared that it would wither plants, weaken men, and excite women. Due to its brightness, the shimmering of Sirius was most noticeable in the variable weather conditions of early summer, indicating, to the Greek observers, certain emanations which caused their malign influence. The people who suffered its effects were called αστροβόλητος (astrobólētos, “struck by the star”). In the literature the star is described as "fiery" or "flaming". The season after the appearance of Sirius became known as the "days of the dog". The inhabitants of Ceos, an island in the Cyclades archipelago, in the Aegean Sea, they offered sacrifices to Sirius and Zeus so that they would bring cool breezes, and they would wait for the reappearance of the star in summer. If it rose clear, it portended good fortune, but, on the other hand, if it rose misty or blurred, it predicted (or rather emanated) pestilence. Some coins from the 3rd century B.C. recovered from the island show dogs or stars from which rays emerge, highlighting the relevance of Sirius. Also in Greece, the astronomer and mathematician Aristarchus of Samos considered the star to be a sun due to its brightness.
Later, the Romans celebrated the setting of Sirius on April 25 by sacrificing a dog to the goddess Robigo along with incense, wine and a sheep, in order to protect the crops that year from diseases such as wheat rust caused by the evil emanations of the star. Likewise, the Romans called the Greek "days of the dog" "canicŭla", a Latin cultism that has been preserved in the Spanish language and retains its meaning, which refers to the evil emanations of the star. days of greater heat, which in Spain happens today in the month of August, although this time of high temperatures before took place after the heliacal rise of Sirius; this temporary displacement is due to the precession of the equinoxes.
Claudius Ptolemy of Alexandria, in the II century, mapped the stars in the seventh and eighth books of his Almagest, an astronomical treatise that contains the most complete stellar catalog of antiquity. In it, Ptolemy used Sirius as the location of the terrestrial central meridian. Interestingly, he drew Sirius as one of the six red stars, something now known not to be true, but nonetheless a controversial issue for astronomers for a long time. The other five red stars are M and K class., such as Arturo, in the constellation of the Boyero, and Betelgeuse, in Orion.
In another part of the world, Polynesia, the brightest stars were important for navigation among the thousands of islands and atolls in the Pacific Ocean. Low, close to the horizon, they served as stellar compasses that helped sailors chart their course to their final destination. Additionally, they functioned as latitude markers; in the case of Sirius, it coincides with the latitude of the Fiji archipelago, at 17º S, so that it surpassed the islands every night. For the Polynesians the map of the night skies was not the same as that of the Romans and Greeks. In its firmament, Sirius belonged to a constellation called Manu, in which it served as the body of a great bird whose wingtips were none other than Canopus to the south and Protion to the north, two other notable stars, which divided the Polynesian night into two hemispheres. In the same way that the appearance of Sirius before dawn heralded summer for the Greeks, for the Maori people it signaled the beginning of winter, in their language called Takurua, a name that designated both the station and Sirius. Its culminating point on the winter solstice was a holiday in Hawaii —an archipelago that, however, is already in the terrestrial northern hemisphere, but at a low latitude—, where it was known as Ka'ulua, "Queen of Heaven", although this is not her only name throughout the Pacific, as she received others such as Tau-ua in the Marquesas Islands, Rehua in New Zealand and Aa and Hoku-Kauopae in Hawaii itself.
In the 18th century, the influential Prussian philosopher Immanuel Kant pondered Sirius and, because of the star's brilliant twinkle in the European sky, where no immediate rivals in brilliance like Canopus, Alpha Centauri or Achernar can be seen, he thought that it would be the center of gravitation of the universe around which the rest of the celestial objects would rotate.
There is an ethnic group in Mali, the Dogon, who are credited with traditional knowledge about Sirius that would theoretically be impossible to acquire without the use of a telescope. According to the books Entretiens avec Ogotemmêli and Le renard pâle, by the French anthropologist Marcel Griaule (1898-1956), this people not only knew the fifty-year orbital period of Sirius and of its small companion star before European and American astronomers, but also made reference to a possible third star in the system. Sirius A is known as Sigi tolo, Sirius B as Po tolo and the third star as Emme ya tolo. Robert K. G. Temple's 1976 book The Sirius Mystery, in which the Dogon are associated with extraterrestrials, further credits them with knowledge of the Jovian system discovered by Galileo Galilei of Jupiter's four largest moons and also the knowledge of Saturn's rings. Such astronomical notions did not go unnoticed and generated controversy and speculation. Based on a 1978 article in the Skeptical Inquirer publication, it is possible that this extraordinary understanding of the Sirius system was the result of cultural contamination, something of which ethnographers themselves have more recently been accused, explanation that on the contrary seems too simplistic for others. Noah Brosch, in his book Sirius Matters, proposed that said astronomical cultural transfer to the Dogon people took place in 1893, when a French expedition that tried to contemplating an eclipse visited his region. Other possible culprits for this alleged cultural contamination could have been missionaries in the year 1930, before Marcel Griaule's first investigations with the Dogons.
Syrian System
Sirius is a binary star composed of two white stars orbiting each other at a distance of about 20 au (about 3 109 km), about the distance between the Sun and Uranus, and a period of fifty years. The brightest component, Sirius A, is a white main-sequence star of spectral type A1V, with an estimated surface temperature of 9940 K. Its companion, Sirius B, is a main-sequence evolved star that has become on a white dwarf. It is currently ten thousand times less luminous in the visual spectrum, but at one time it was the more massive of the two. The age of the system has been estimated at around 230 million years. It is believed that earlier in its existence there were two bluish-white stars each traveling in an elliptical orbit every 9.1 years. The infrared radiation emission from the Sirius system is higher than expected, based on measurements by the space observatory IRAS, which could be evidence of dust in the system and is considered unusual for a binary star. The Chandra X-ray Observatory image shows Sirius B eclipsing its theoretically brighter companion, as Sirius B is a more powerful source of X-rays.
Syrian A
Sirius A has a mass of about 2.02 times that of the Sun, which is 1.9891 1030 kg. The radius of Sirius A, 5.936±0.016 mas, has been measured with an astronomical interferometer. Its rotational speed is relatively low, 16 km/s, due to which there is no significant bulging of the disk, contrary to what happens to a star of similar size, Vega, which due to its high With a rotation speed of 274 km/s it has a much more prominent equatorial diameter than the polar one. While Sirius's apparent magnitude is the largest in the night sky as far as stars are concerned, at –1.46, its magnitude absolute is 1.42, well below its neighbors Iota Canis Maioris, Bellatrix or VY Canis Maioris. Its age is around 200 or 300 million years.
Theoretical stellar models indicate that the star formed during the collapse of a molecular cloud and, after ten million years, its internal energy generation came entirely from nuclear reactions. The core became a convective zone and used the CNO cycle to generate power. Sirius A is expected to exhaust the hydrogen reserves in its core within a billion years after its formation. It will then become a red giant and then end up as a white dwarf.
The specter of Sirio A reveals strongly metal lines, that is, a star rich in helium-rich elements, such as iron. Compared to the Sun, the proportion of iron versus hydrogen in the atmosphere of Sirio A is given by: [chuckles]FeH]=0,5{displaystyle {begin{smallmatrix}[{frac {Fe}{H}}}=0.5end{smallmatrix}}}}}}equivalent to 100.5, which means Sirio A has 316 % of the proportion of iron-hydrogen in the Sun's atmosphere. On the other hand, it is unlikely that this percentage of metallic elements is the same in the entire star; it could be suspended in a thin layer of convective on the surface.
![{displaystyle {begin{smallmatrix}[{frac {Fe}{H}}]=0,5end{smallmatrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/ea6fa4145d62f33f2bc87e4024733884d15692a0)
Sirius B
Sirius B is the closest white dwarf to Earth. It has a mass almost equal to that of our Sun (0.98 M☉), which places it as one of the the most massive white dwarfs of which there is news, since on average they usually have half the solar mass, only to this we must add that, having the same mass as the Sun, its size is more like that of the Earth, so its density is very high. The surface temperature of Sirius B has been estimated at 25,200 K, but although this temperature is higher than that of Sirius A, there are no internal sources of energy, so the star will progressively cool over a period of more than two thousand. million years in which it will radiate its heat into outer space. The apparent magnitude of Sirius B is 8.30, so it would be easily observable in a telescope if we were not dazzled by the larger magnitude of Sirius A. Its absolute magnitude is low, only 11.18.
A white dwarf only forms after a star develops from the main sequence and goes through a red giant stage. In the case of Sirius B, this happened when the star was only half its current age, about 120 million years ago. During its time on the main sequence the initial star, of type B (or B4-5), would have a mass of about 5 M☉. During its intermediate Sirius B phase as a red giant, Sirius A could have increased its metallicity.
The composition of Sirius B is basically a mixture of carbon and oxygen from the fusion of helium in its previous stage. There is a convective envelope of other lighter elements, segregated according to their mass as a consequence of the high surface temperature; hence the outer atmosphere of Sirius B is made of practically pure hydrogen (the lightest element) and no other elements are visible in the spectrum of this star.
Speculation on Sirius C
Since 1894, some visible irregularities in the orbit of the Sirius system suggested a third, even smaller component, something that has never been confirmed. The best fit to the data indicates that it would have an orbit around Sirius A of about six years and a mass of only 0.06 M☉ and would be up to ten times fainter than Sirius B, which it would tremendously complicate its visualization. In the 1920s several astronomers repeatedly observed a small star in the vicinity of Sirius A, but later lost sight of it. Later studies were able to confirm that it was a background object; In 1999, a team of French astronomers was able to examine the surroundings of Sirius A in search of a faint star and found, in the background, a star of similar brightness that in the first half of the 1920s must have been located in the visual zone occupied by Sirius. A. The most recent images failed to find any companion stars to Sirius A within a 30 arcsec field. Additional observations were published in 2008 that failed to detect either a third star or a planet.
Possibility of life around Sirius
The distance from Sirius A at which a planet would have to be to host physical conditions favorable to life as we know it is 4.7 au, about 700 million kilometers. However, at this distance a stable orbit could not exist due to the disturbances caused by the presence of Sirius B. Any habitable planet would have been destroyed after the expansion of the latter during its red giant stage and, in the event that Had it formed as a result of this process, it would be subjected to an incessant rain of comets and asteroids, since around Sirius a dust disk similar to the one that occupied the solar system in its early stages has been detected.
Discovery of Sirius B
In 1844, the German astronomer Friedrich Bessel, recognized for being the first to discover the trigonometric parallax in 1838, deduced in 1844, from the oscillations in the proper motion of Sirius, that it had an invisible companion, which puzzled the entire astronomical community. Thanks to the analysis of the trajectory, some characteristics of the Sirius system could be calculated. Almost two decades later, on January 31, 1862, the American astronomer and telescope manufacturer Alvan Graham Clark, from the Alvan Clark & Sons, located in Massachusetts, was the first to sight Sirius's faint companion star, now called Sirius B and also, colloquially, "the Pup". Interestingly, he was not looking to make out the new star, but to test the lenses of his new refracting telescope—the largest in the world of its kind at the time, with a 480 mm aperture, destined for the Dearborn Observatory—and discover imperfections thanks to the brightness of Sirius. From then on, Sirius was no longer an astrometric binary star, Yo. e., binary but apparently solitary to the naked eye or telescope, to fall into the category of visual orbital binary stars.
In 1851 Christian Peters had been able to estimate the orbital period of the couple at 50,093 years, and their mass at more than six times that of Jupiter, although in the latter his calculations fell short. Likewise, he verified a strong eccentricity in the orbital trajectory of Sirius B and provided an ephemeris with the expected positions.
In 1915, Walter Sydney Adams, using a 1.5m reflecting telescope at Mount Wilson Observatory, observed the spectrum of Sirius B and determined that it was a faint whitish star, leading astronomers to believe that it was a white dwarf, the second in history to be discovered, or even the first according to other sources. Over the years it has become one of the three "classical" white dwarfs, along with 40 Eridani and the Star of Van Maanen.
The first measurement of the diameter of Sirius A was carried out by Robert Hanbury Brown and Richard Q. Twiss in 1959 at Jodrell Bank, with the help of their Stellar Intensity Interferometer, but it was not until 2005 that, with the Hubble Space Telescope, it was possible to define the size of Sirius B: it has approximately the same diameter as Earth, about 12,000 km, but with a mass slightly less than that of the Sun.
Visibility and observation
With an apparent magnitude of –1.46, Sirius is the brightest star in the night sky, nearly twice as bright as the second-brightest star, Canopus, at –0.62 according to the Hipparcos catalogue. However, it is surpassed by the Moon, by Jupiter and by Venus; sometimes even the apparent magnitude of Mercury and Mars is greater. Sirius can be seen from almost any inhabited place on Earth. Only those who live beyond the 73rd parallel, several degrees above the Arctic Circle, cannot see it; and from some towns at high latitudes, although it can be seen, it rises very little above the horizon, for example in the Russian city of Saint Petersburg, where it only reaches 13º above it. Together with Procion and Betelgeuse, it forms the triangle of winter for observers in the northern hemisphere. Due to its declination of just -17°, Sirius becomes a circumpolar star at latitudes ranging from 73º S to the South Pole. In early July, from the southern hemisphere, Sirius can be seen both at sunset, as it sets behind the Sun, and at sunrise, when it appears before it.
Given the right conditions, Sirius can be seen in daylight with the naked eye. It is necessary that, with Sirius at the zenith and the Sun low on the horizon, the sky is clear and the observation site is located at a high altitude; meeting these requirements is more easily met in the southern hemisphere because of of the declination of Sirius. During the night, one of the most popular stellar alignments is that the prolongation of the imaginary line created by the three main stars in Orion's belt —Alnitak, Alnilam and Mintaka— goes to Sirius towards the southeast, at about 20º, and to Aldebaran to the northwest.
The orbital movement of the binary system of Sirius means that the minimum angular separation between the two stars is less than three seconds of arc and the maximum is twelve seconds of arc. If the first of the exposed situations is applied, distinguishing the small Sirius B from its large companion is challenging for the observer, since a telescope with at least 300mm aperture is required supported by excellent observing conditions. In general, the main obstacle to observing Sirius B is given by the large difference in magnitude between the primary and secondary star. Since 1994, when the last periastrum of the Sirius system occurred, the pair have been drifting apart., which makes it easier to see them separately. Also, to differentiate both stars, a polygonal diaphragm, devised by Alexander Aitken, can be useful, which modifies the light coming from Sirius A so that Sirius B is no longer imperceptible between the brightness of the first. The last apoastro took place in the year 2018, when the system was separated by 12 arcsec with a position angle of 66º; the previous one happened in 1966, so until 2010 it was not so easy to distinguish one from the other.
At a distance of 2.6 parsecs (8.6 light-years), the Sirius system contains two of the eight closest stars to the solar system and is the fifth closest star system to us. It is this proximity, and not the actual luminosity of Sirius, the main reason why its apparent magnitude follows Moon, Jupiter and Venus on the list, identically to what happens with other nearby stars like Alpha Centauri and in clear contrast to what happens with supergiant stars and extremely luminous like Canopus, Rigel or Betelgeuse, which despite being much farther away are among the brightest in the firmament. Despite everything, we must not forget that Sirius is around twenty-five times more luminous than our Sun.
Using Sirius as a distance reference, the nearest large star is Procyon, 1.61 parsecs (5.24 light-years) away. The Voyager 2 space probe, launched in the year 1977 in order to study the gas giants of the solar system, pass at a maximum distance of 1.3 pc (4.3 light-years) from Sirius in approximately 296,000 years.
Gloss Comparison
Sirius is currently the brightest star in the sky, but that won't always be the case. Around the year 235,000 AD. C., Vega will replace Sirius in that first position with a magnitude of –0.7, and before the year 260,000 AD. C., with a magnitude of -0.46, Canopus could regain its second place to the detriment of Sirius, which would fall on the list to become the third brightest star from Earth. The evolution of the brightness of Sirius in comparison with other very bright stars, in the space of time that goes from one hundred millennia before Christ to one hundred millennia after Christ is shown in the following diagram and its corresponding numerical table:
Year
(a. C./d. C.)Sirio Canopus Vega Arturo Proceedings Altair α Cen −100,000 −0.66 −0.82 +0,33 +0.88 +0.88 +1.69 +2.27 −75000 −0.86 −0.80 +0,24 +0,58 +0.73 +1.49 +1.84 −50000 −1.06 −0.77 +0.17 +0,30 +0,58 +1.27 +1.30 −25000 −1,22 −0.75 +0.08 +0.08 +0.46 +1.03 +0.63 0 −1,43 −0.72 0.00 0.02 +0,37 +0,78 −0,21 25000 −1,58 −0.69 −0.08 +0,02 +0,33 +0,49 −0.90 50000 −1.66 −0.67 −0.16 +0,19 +0,32 +0,22 −0.56 75 000 −1.66 −0.65 −0.25 +0.45 +0,37 0.06 +0,30 100 000 −1.61 −0.62 −0.32 +0.74 +0.46 −0.31 +1.05
Sirius as a red star
The paradox that Sirius was until recently (in stellar terms) a red star surprised astronomers, because although it is known for certain that it is bluish-white, historical documents denoted that the star was red.
In Ancient Egypt, for whose inhabitants Sirius was of great importance given the relationship between its heliacal rise and the rise of the Nile, Sirius was a red star and, likewise, around the year 150 AD. C. Claudius Ptolemy described Sirius with a reddish color, along with five other stars that, in effect, are reddish or orange: Betelgeuse, Antares, Aldebaran, Arturo and Pollux. The first to officially disagree was the amateur astronomer Thomas Barker, a landowner of Lyndon Hall in Rutland, UK, who spoke on the subject at a meeting of the Royal Society in London in 1760. The existence of stars that varied in brightness gave rise to the idea that there might also be stars that varied in brightness. that they change out their color; Sir John Herschel made this point in 1839, possibly influenced by his study of Eta Carinae two years earlier. Thomas Jefferson Jackson See reopened the debate about the red color of Sirius by publishing various papers in the year 1892 and a summary in 1926, in which he not only resorted to Ptolemy, but also cited the poet Arato, Marco Tulio Cicero and Julio César Germánico as people who had described the star as red, admitting on the other hand that none of the three were astronomers. The Roman philosopher Lucius Anneus Seneca had also at the time described Sirius as having a darker red color than Mars, further stating "Sirius is red". It should be noted that, although it was The most widely held idea, not all ancient observers saw Sirius red. In fact, in ancient China Sirius was the reference to take as a white star, and multiple records from the 2nd century BC. C. until the 7th century AD. C. describe Sirius with white tones. Returning to Europe, already in the first century the poet Manilius defined it as "sea blue", an image repeated in the IV by Avieno.
In 1985, German astronomers Wolfhard Schlosser and Werner Bergmann published a report of an eighth-century Lombard manuscript containing De cursu stellarum ratio, written by Saint Gregory of Tours. The text, in Latin, taught readers how to determine the time of night prayer thanks to the positions of the stars in the sky, adjectives Sirius with the word rubella, "reddish". They based themselves on this fact to justify that Sirius B was a red giant at that time. However, others replied that Saint Gregory of Tours was probably referring to Arthur instead of Sirius.
The possibility that these found positions have been caused by stellar evolution from either Sirius A or Sirius B has been ruled out by astronomers, because the time elapsed has been too short for a star and because there is no signs of the nebulosity that would be expected in the system if such a large change had taken place. Interaction with a presumed third star, not yet known, has even been proposed as the cause of the red color. Some other alternative explanations They have argued that either the red star was described as a metaphor for bad luck or that the flickering of Sirius gave the impression of red hues.
The final explanation that solved the mystery was much simpler: just as happens with the Sun when it is low on the horizon, at sunrise or sunset, Sirius appeared red in that same position, as a consequence of the scattering of light through the atmosphere. Hence Sirius was red for the Egyptians, for example, since in its heliacal rise it is located low in the sky.
Nearby Celestial Objects
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When observing the night sky, Sirius is a good reference to locate oneself in the sky. In the vicinity of Sirius there is an object belonging to the Messier catalogue, M41, an open cluster in which dozens of of stars, predominantly yellow, of magnitudes from 8 to 10, approximately, which gives the whole a magnitude of 5.0. M47, already in the constellation of Puppis; and to the north, in the constellation of Monoceros, is the open cluster M50. To the west of Sirius, and slightly to the south, is Beta Canis Maioris, which despite its name is not the second brightest star in the constellation, but rather the fourth; It is a slightly variable blue giant whose absolute magnitude far exceeds Sirius, but lies much further from the solar system. The second most luminous star in appearance of Canis Maior is actually Adhara, Epsilon Canis Maioris, another blue giant that is already located much further south in the constellation. Near Sirius one can also observe double or triple stars such as μ CMa, S 516, S 518 or ν1 CMa, the latter orange in color very close to two others with the same name and similar hue, ν2 CMa and ν3 CMa; of these three, the closest to Sirius in the sky is ν 3 CMa. It is also worth mentioning the presence of clusters such as NGC 2345, NGC 2204 or NGC 2360.
Movement
In 1718, Edmund Halley discovered the proper motion of the hitherto supposed fixed stars, after comparing the astrometric measurements of his time with those given by Ptolemy in his Almagest. He realized that the stars Aldebaran, Arthur, and Sirius had moved significantly, in the case of Sirius up to 30 arcmin in a southerly direction—which is a distance similar to the apparent lunar diameter—in about 1,800 years.
A century and a half later, in 1868, Sirius became the first star to have its velocity measured. Sir William Huggins analyzed the spectrum of the star and noted an approach to red, so he concluded that Sirius was moving away from the solar system at a speed of about 40 km/s. However, this Huggins' measurement was exaggerated in magnitude and wrong in sign, given current measurements, which indicate that Sirius is moving at –7.6 km/s, which means that it is traveling more slowly and is not receding. from us, but is approaching the solar system. The positive part of Huggins's study was that he introduced the study of stellar radial velocities. Within about 64,000 years Sirius will reach the minimum distance from the solar system, about 7.86 light-years, at which time its apparent magnitude will also be greater than at present and will grow to -1.68. After that time, Sirius will begin to move away from the Sun.
Sirius has a relatively large proper motion of 1.3 arcsec per year, of which about 1.2 arcsec is southbound and 0.55 arcsec is westbound.
Sirius Super Cluster
Ejnar Hertzsprung, in 1909, noticed that Sirius could be part of the Ursa Major stream, based on the proper motion of Sirius. This Ursa Major stellar group is a group of 220 stars that share their movement through the galaxy and that initially arose in an open cluster that since then has been losing its gravitational force. However, studies carried out in 2003 and 2005 question whether Sirius belongs to the current, because the Group of the Ursa Major has an estimated age of 500±100 million years, while Sirius, with a metallicity similar to that of the Sun, is only half as old, meaning it is too young to belong to the group. Instead, Sirius could belong to a proposed Sirius supercluster, which would include other scattered stars, including Beta Aurigae, Alpha Coronae Borealis, Beta Crateris, Beta Eridani, and Beta Serpentis. This cluster would be one of it There are three located within 150 pc (500 light-years) of the Sun, along with the Hyades Cluster and the Pleiades Cluster, each of which contains hundreds of stars. An alternative interpretation is that the current of the Hyades and Sirius are not made up, respectively, of stars with the same origin, but of stars with no affinity between them to which irregularities in the Milky Way's gravitational field have stamped a common pattern of motion. Therefore, one should not speak of a supercluster, but rather a "dynamic current".
In popular culture
References to Sirius have been frequent in the literary tradition. John Milton mentions her in his poem "On the Fifth of November", and Tennyson refers to her in "The Princess". In science fiction stories, as well as in popular culture, it is quite recurrent. As early as 1752, Voltaire wrote a philosophical tale about a being from Sirius, Micromégas, who could be a precursor of the genre. of science fiction. The characters of Branch Revealed , by Arthur C. Clarke and Gentry Lee, go to the Sirius system aboard a generation ship. Sirius is also the name of the ship on which Tintin goes in search of the remains of the Unicorn in The Treasure of Red Rackham. The astronomer Noah Brosch has made conjectures about the name of the character Sirius Black in the series of novels Harry Potter by J. K. Rowling, since according to him the author could have been inspired by Sirius B (Sirius B in English), and emphasizes his relationship with dogs, as he is a character who can transform into a dog.
In the audiovisual field, the American satellite radio company Satellite CD Radio changed its name to Sirius Satellite Radio in November 1999, for the reason of calling itself "the brightest star of the night sky". Earlier, in the television series V, the aliens arriving on Earth had departed from a supposed fourth planet around Sirius.
In music, the German composer Karlheinz Stockhausen is credited with having affirmed on different occasions that he came from a planet located in the Sirius system. On the other hand, it is worth noting the short instrumental theme "Sirius" from the album Eye in the Sky by the international projection group The Alan Parsons Project. This song, which on the album leads to the single "Eye in the Sky", was popularized in part for its use in sporting events, especially in the NBA and more precisely by the Chicago Bulls of the time of Michael Jordan. Other albums that can be cited are Lemuria Sirius B by the Swedish band Therion, or the concept album From Mars to Sirius by the French Gojira.
Regarding institutions and their symbols, perhaps the most significant fact is that Sirius is present on the Brazilian flag, since it is one of the twenty-seven stars drawn on it, where it represents the Brazilian state of Mato Grosso, to the west of the country and one of the largest. Notably, on the flag it is one of the stars arranged on the left side of the central circle. Sirius appears on the coat of arms of Macquarie University, located in Sydney, and is also the name of its student publication.
In theosophy, it is believed that the Seven stars of the Pleiades transmit the spiritual energy of the seven rays of the galactic logos to the seven stars of the Dipper Major, and then move on to Sirius. From there it is sent through the Sun to the god of the Earth, Sanat Kumara, and finally through the seven Masters of the seven rays to the human race.
In the military naval sphere, Sirius is quite present. Seven ships of the British Royal Navy have been christened HMS Sirius since the 18th century. The first of these, originally chartered in 1786, was the flagship of the First Fleet which sailed for Australia in 1788. The Royal Australian Navy later named one of their ships HMAS Sirius (O 226) after the former British flagship. Among the American ships there is a USNS Sirius (T-AFS-8). In civil navigation, the Italian liner Sirio, dedicated to transporting European emigrants to South America, sank off the coast of Cabo de Palos in Cartagena (Spain) in 1906, a serious incident in which more than two hundred people. In aeronautics, an aircraft related to Sirius was built in the United States, the Lockheed Model 8 Sirius, the first of which was flown by Charles Lindbergh, a famous aviator who was the first to cross the Atlantic Ocean non-stop in lonely. Continuing in the world of transportation, the Mitsubishi Motors company designed the Mitsubishi Sirius engine in 1980.
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Sagitta
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