Sirius

Sirius A/B

The position of Sirius.
Observation data
Epoch J2000
Constellation Canis Major
Right ascension 06h 45m 08.9s
Declination -16° 42' 58"
Apparent magnitude (V) -1.43/8.44
Characteristics
Spectral type A1 V/DA2
B-V colour index 0.00/-0.03
U-B colour index -0.05/-1.04
Variable type None
Astrometry
Radial velocity (Rv) -7.6 km/s
Proper motion (μ) RA: -546.01 mas/ yr
Dec.: -1223.08 mas/ yr
Parallax (π) 380.02 ± 1.28 mas
Distance 8.58 ly (2.631 pc)
Absolute magnitude (MV) 1.47/11.35
Details
Mass 2.14/0.98 M☉
Radius 1.68/0.008 R☉
Luminosity 26.1/0.00024 L☉
Temperature 9,900/24,790 K
Metallicity 1,000%/?
Rotation
Age 2-3 × 108 years
Other designations
α Canis Majoris, 9 CMa, HD 48915, HR 2491, BD -16°1591, Gl 119-052, GCTP 1577.00 A/B, GJ 244 A/B, LHS 219, ADS 5423, LTT 2638, HIP 32349.

Sirius (α CMa / α Canis Majoris / Alpha Canis Majoris) is the brightest star in the nighttime sky, with a visual apparent magnitude of −1.46. It is located in the constellation Canis Major. Its name comes from the Latin sīrius, from Greek σείριος (seirios, "glowing" or "scorcher"). As the major star of the "Big Dog" constellation, it is often called the "Dog Star".

Sirius can be seen from every inhabited region of the Earth's surface and, in the Northern Hemisphere, is known as a vertex of the Winter Triangle.

At a distance of 2.6 pc or 8.57 light years (50.3 trillion miles), Sirius is also one of the nearest stars to Earth. The best time of year to view it is around January 1, when it reaches the meridian at midnight.

It is a main sequence star of spectral type A0 or A1 and has a mass about 2.4 times that of the Sun.

It is also known by the Latin name Canicula ("little dog") and as الشعرى aš-ši’rā in Arabic astronomy, from which the alternate name Al Shira derives.

In Chinese culture, the star is known as 天狼星 (literally, heavenly wolf star).

Its closest large neighbour star except Sirius B is Procyon, 1.61 pc or 5.24 ly away.

In 1909, Ejnar Hertzsprung suggested that Sirius was part of the Ursa Major Moving Group; however, more recent research by Jeremy King et al. at Clemson University in 2003 questions whether that is true, since the two components of Sirius appear to be too young.

Binary system

In 1844 Friedrich Wilhelm Bessel deduced that Sirius was actually a binary star. In 1862 Alvan Graham Clark discovered the companion, which is called Sirius B, or affectionately "the Pup". The visible star is now sometimes known as Sirius A. The two stars orbit each other with a separation of about 20 AU and a period of close to 50 years.

In 1915 astronomers at the Mount Wilson Observatory determined that Sirius B was a white dwarf, the first to be discovered.

Interestingly, this means that Sirius B must have originally been by far the more massive of the two, since it has already evolved off the main sequence. Robert Hanbury Brown measured the diameter of Sirius for the first time in 1956. In 2005, using the Hubble Space Telescope, astronomers determined Sirius B to be 12,000km (7,600 miles) in diameter, with a mass that is 98% of the Sun. [1]

History

Historically, many cultures have attached special significance to Sirius. Sirius was worshipped as Sothis in the valley of the Nile long before Rome was founded, and many ancient Egyptian temples were oriented so that light from the star could penetrate to their inner altars. The Egyptians based their calendar on the heliacal rising of Sirius, which occurred just before the annual flooding of the Nile and the Summer solstice. In Greek mythology, Orion's dog became Sirius. The Greeks also associated Sirius with the heat of summer: they called it Σείριος Seirios, often translated "the scorcher." This also explains the phrase "dog days of summer".

In the astrology of the Middle Ages, Sirius was a Behenian fixed star, associated with beryl and juniper. Its kabbalistic symbol Image:Agrippa1531_Canismaior.png was listed by Heinrich Cornelius Agrippa.

Mysteries

The image of Sirius A and Sirius B taken by Hubble Space Telescope A – bigger, B – smaller white dwarf (Credit:NASA)
The image of Sirius A and Sirius B taken by Hubble Space Telescope A – bigger, B – smaller white dwarf (Credit:NASA)

There are a few unsolved mysteries regarding Sirius.

  • Firstly, apparent orbital irregularities in Sirius B have been observed since 1894, suggesting a third very small companion star, but this has never been definitely confirmed.
  • Second, ancient observations of Sirius describe it as a red star, when today Sirius A is bluish white. The possibility that stellar evolution of either Sirius A or Sirius B could be responsible for this discrepancy is 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. 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/blue hues when near the horizon.

The Dogons

It has been suggested that the Dogon tribe of Mali knew about unseen companion star(s) before they were discovered in the 19th century. This is a source of speculation for UFO enthusiasts and was the subject of the book The Sirius Mystery by Robert Temple, who linked this to the legends of the Dogon as well with the legends and traditions of the ancient Egyptians and Sumerians, conjecturing that aliens from Sirius had visited Earth and influenced early civilization. This work has been challenged by astronomer Carl Sagan, among others, as based on selective evidence. Careful research reveals there may have been cultural contamination on the part of visiting astronomers who went to the region to observe a transit of Venus, though this is still a matter of some dispute.

Sirius in popular culture

An artist impresion of Sirius A and Sirius B, A – bigger, B – smaller white dwarf (Credit:NASA)
An artist impresion of Sirius A and Sirius B, A – bigger, B – smaller white dwarf (Credit:NASA)
  • Sirius is the home star of one of the main characters of Voltaire's Micromegas.
  • In the Known Space series of stories by Larry Niven a high gravity world called " Jinx" is the moon of a gas giant in the Sirius system.
  • In Doris Lessing's Canopus in Argos series, star-visitors from Sirius play a part in Earth's history, though secondary to the Canopans. They feature especially in The Sirian Experiments
  • In the fantasy novel Dogsbody by Diana Wynne Jones the star Sirius is an intelligent being falsely accused of murdering another star by his peers. As punishment he is sent to Earth in the body of a new born puppy to find the weapon he supposedly used.
  • In the Serious Sam video games, Sirius is the heavenly body from which the evil presence, Mental, is commanding its armies. The term "Serious Sam" is therefore a pun since much of the game's story revolves around Egyptian culture being influenced by aliens from the Sirius system under Mental's control.
  • Olaf Stapledon's Sirius is about a dog with human intelligence, and who also has mystic visions.
  • In the Harry Potter book series, the character Sirius Black, who can change shape into a large black dog, takes his name from the star.
  • Sirius is the home star system of the "visitors" in the TV series V.
  • Sirius figures into Cosmic Trigger by Robert Anton Wilson.
  • Sirius is mentioned in Les Misérables by Victor Hugo, en passant.
  • The Sirius Cybernetics Corporation receives a mention in Douglas Adams's The Hitchhiker's Guide to the Galaxy.
  • Tom Robbins' 1994 novel, Half Asleep in Frog Pajamas deals greatly with various Dogon/Sirius mysteries as well as much of the general mythology surrounding the star.
  • In the computer game Freelancer some people escape war-ravaged Earth to start over in the Sirius System.
  • There is also a metal & plastic yo-yo named after the Sirius star. It is manufactured by a company called YoYoJam and is the signature model of Nathan Crissey.
  • In the Atomic Betty episode "Toxic Talent", the song she performs in that episode is ironically called, "Dog Star Sirius".
  • Sirius is also the origin of the name for Sirius Satellite Radio (and its mascot, the dog).
  • Mondo 2000 co-founder and cyberpundit R. U. Sirius used the "Sirius" in his pseudonym as a reference to the star, in addition to the more obvious play on words.
  • In the Myst games, the character Sirrus probably has his name from Sirius, while his brother Achenar got his from the star Achernar.
  • In the anime Voices of a Distant Star (or Hoshi no Koe), a human expedition of four intergalactic spaceships travels to the Sirius star system to chase down enemy aliens called Tarsians. The anime also features the (fictional) fourth planet of the star system called Agharta.
  • "Sirius" is the title of the 1987 song and album by Irish folk/ new age band Clannad, in reference to the star.
  • The Bag On Line Adventures (a.k.a The story of Coheed and Cambria) describes the "Seven Stars of Sirius" as giant star-transformers that hold together the Keywork (a vast structure of 12 sectors/78 planets) and Heaven's Fence.