Sirius

Position and location of Sirius

Sirius, also known as Alpha Canis Majoris or the Dog Star, is the fifth closest star to our Solar System at 8.6 light years, and the brightest star in the sky with an apparent magnitude of -1.46. It is located in the Constellation Canis Major and is a binary star system.

History

Sirius A was known throughout human history and was referred to Sopdet by the ancient Egyptians. The Middle Kingdom of Egypt even based their calendar on the first day Sirius would become visible right before sunrise, to indicate the coming annual flooding of the Nile. The ancient Greek name for Sirius was Σείριος Seirios, which was derived from σείριος, meaning scorching or destructive. It was seen as a as a herald that forewarned of a hot and dry summer ahead.

Ptolemy was the first to actually map the star in the sky, recorded in the Almagest, or Great Book. In 1833-34, Friedrich Wilhelm Bessel, concluded that Sirius must have a companion after studying the motions of the star. The first observable evidence of a companion star didn't occur though until 1862, when Alvan Graham Clark found Sirius B at the Dearborn Observatory. In 1915, using the Mount Wilson Observatory, Walter Sydney Adams was the first to discover it as a white dwarf. Although the companion was first measured in 1959, it wasn't until 2005, using the Hubble Space Telescope, was an accurate measurement calculated.

The stars

The two stars in the Sirius binary system orbit each other with an average distance of 19.8 AU (around the distance of Uranus from the Sun), which takes around 50 years to complete. Sirius A is a star of spectral type A1V. Sirius B is a white dwarf star, which were once a more massive main sequence star then its companion. Scientists estimate the age of the system is only some 230 million years old.

Sirius A

Sirius A is the star that is seen from Earth and known since ancient times, it is the brightest star in the night sky. As an A1V class star, it appears somewhat bluish in color. The star is estimated to be over 2 times Sol’s mass and 1.68 to 1.71 its diameter. Sirius is also much hotter with a surface temperature 9,940K, but the largest difference between the star and our sun is the luminosity, where Sirius is more than 21 times brighter. Because of extreme brightness and temperature, the star is expected only to last another billion years before leaving the main sequence and becoming a Red Giant.

Sirius B

Nicknamed “the Pup”, Sirius B is a classified as a white dwarf DA2-5, and is more than 8,200 times as fainter then it's primary (360 times fainter then our Sun). Because the star is a white dwarf, it is extremely dense, holding 97.8% of the Sun's mass but is only 12,000 km in diameter, slightest smaller then the Earth. Scientists theorize the star was once one of a spectral class B stars much like Regulus before becoming a red giant and finally a white dwarf.

Disambiguation

Sirius. also known as Sirius XM Radio, Inc. is also a subscription radio service most famous for hiring Howard Stern, but also offers a wide variety of stations appealing to different tastes, including stations devoted to Christian singers and Christian themes. Sirius merged with XM Satellite Radio on February 18, 2008.