Sirius

Observational Data
Designation |  Alpha Canis Majoris
Right ascension |  06h 45m 08.9173s
Declination |  −16o 42′ 58.017″
Constellation |  Canis Major
Type of object |  Binary star
Magnitude |  Apparent: -1.46(star A)/8.30(star B)
Absolute: 1.42(star A)/11.18(star B)
Astrometry
Distance from Earth |  8.6 ly
Radial velocity |  −7.6 km/s
Proper motion |  RA: −546.05 mas/yr
Dec.: −1223.14 mas/yr
Parallax |  379.21 ± 1.58 mas

Sirius, also known as Alpha Canis Majoris or the Dog Star, is the fifth closest star (counting Proxima Centauri as a separate star) to our Solar System at a distance of 8.6 light years, and the second closest binary star system. Sirius is also the brightest star in the night sky with an apparent magnitude of -1.46.[1] The star is located in the constellation Canis Major, and is one of the three stars that make up the Winter Triangle.

## Contents

* 1 History
* 2 The stars
* 2.1 Sirius A
* 2.2 Sirius B
* 3 Disambiguation
* 4 References

## History[edit]

Sirius A was known throughout human history and was referred to Sopdet by the ancient Egyptians. The Middle Kingdom of Egypt even based its calendar on the first day Sirius would become visible right before sunrise, to indicate the coming annual flooding of the Nile.[2] 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.[3]

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.[4] 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[edit]

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 was once a more massive main sequence star then its companion.

### Sirius A[edit]

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.

For an Earth-like world that has liquid water on it to exist around Sirius, it would need to be around 4.6 AUs away, equivalent to the distance of Jupiter from the Sun, with an orbital period of 6.8 years. However, due to the close orbit of Sirius B, it would be difficult for a planet to form, due to the star's disruptive influence. If such a world did manage to form however, it also may be disrupted by the mass loss of Sirius B when it became a white dwarf.

### Sirius B[edit]

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 than the Earth.[5] 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.[6]

## Disambiguation[edit]

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.

## References[edit]

1. ↑ http://www.atlasoftheuniverse.com/stars.html
2. ↑ https://books.google.com/books?id=qUk0GyDJRCoC&pg=PP1&dq=isbn=0306466120&sig=wDa9MW9Qy5f3BIvPvbDLc_LMnJE#PPA500,M1
3. ↑ http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Canis_Major*.html
4. ↑ http://adsabs.harvard.edu/abs/1915PASP...27..236A
5. ↑ http://hubblesite.org/newscenter/archive/releases/2005/36/text/
6. ↑ http://solstation.com/stars/sirius2.htm

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Acrux · Alpha Centauri · Luyten 726-8 · Sirius