Sirius
This article is about the star. See Sirius (disambiguation) for other uses of the name.
Sirius (
&alpha Canis Majoris, also known as the
Dog Star) is the brightest
star (-1.46
m) in the
night sky.\nThis star 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. \nAt a distance of 8.6
light years, Sirius is also one of the
nearest stars to Earth. \nIt is a
main sequence star of
spectral type A0 or A1 and has a mass about 2.4 times that of the
Sun.
In
1841[?]
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
Mt. Wilson Observatory discovered that Sirius B was a
white dwarf, the first to be discovered. Interestingly, this means that Sirius B must have originally been much the more massive of the two, since it has already evolved off the main sequence.
\n
History
Historically, many cultures have attached special significance to Sirius.\nSirius was worshipped in the valley of the Nile long before Rome was founded, and many ancient Egyptian temples were constructed oriented so that light from the star could penetrate to their inner altars. \nThe Egyptians based their calendar on the heliacal rising of Sirius, which occurred just before the annual flooding of the Nile and the Summer solstice. \nIn Greek mythology, Orion's dog became Sirius. \nThe Greeks also associated Sirius with the heat of summer: the name Sirius is derived from Seirios meaning "the scorcher". This also explains the phrase "dog days of summer".
There are a few unsolved mysteries regarding Sirius. \nFirstly, it has been suggested that there is a third very small companion star, but it appears that this has not yet been definitely confirmed. \nSecondly, ancient observations of Sirius describe it as a red star, when today Sirius A is bluish white. The possibility that stellar evolution of either\nSirius 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.\nA third mystery is a suggestion that the Dogon tribe of Africa knew about unseen companion star(s) before they were discovered in the 19th century.\nThis is a source of speculation for UFO enthusiasts and was the subject of the book The Sirius Mystery by Robert Temple.
Some facts about Sirius A
Some facts about Sirius B
See also
\n* List of nearest stars
References and external links
Category:Stars
