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Sirius

[Categories: Binary stars, Canis Major constellation, Stars]

/This article is about the star. 

*Sirius* 

*Canis Major* A constellation southeast of Orion; contains SiriusCanis
Major is the brightest *star*

This 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*

At a distance of 8.6 *light year*s, Sirius is also one of the nearest
stars to Earth. It is a *main sequence* 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 *Mount 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 the much
more massive of the two, since it has already evolved off the main
sequence.

History

Historically, many cultures have attached special significance to Sirius.
Sirius was worshipped in the valley of the *Nile* long before *Rome* was
founded, and many *ancient Egypt*ian temples were constructed 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: 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.

Firstly, it has been suggested that there is a third very small companion
star, but it appears that this has not yet been definitely confirmed.

Secondly, 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.

A 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,
although careful research reveals this was probably cultural contamination
on the part of visiting astronomers who went to the region to observe a
*transit of Venus*

Some facts about Sirius A

*Parallax* 0.379 arcsecs

Spectral type: A1 V

*Radial velocity* Velocity along the line of sight toward or away from the
observer ?9 km/s

*Proper motion*: 1.339 arcsecs/year

Apparent visual magnitude: ?1.44

*Absolute visual magnitude* 1.45

*Luminosity* 26.1 Solar Luminosities