Wed, 2018-Mar-21 00:11 UTC
Length - 3:35
Welcome to featured Wiki of the Day where we read the summary of the featured Wikipedia article every day.
The featured article for Wednesday, 21 March 2018 is Capella.
Capella, also designated Alpha Aurigae (α Aurigae, abbreviated Alpha Aur, α Aur), is the brightest star in the constellation of Auriga, the sixth-brightest in the night sky, and the third-brightest in the northern celestial hemisphere after Arcturus and Vega. A prominent star in the winter sky of the northern hemisphere, it is circumpolar to observers north of 44°N. Its name meaning "little goat" in Latin, Capella depicted the goat Amalthea that suckled Zeus in classical mythology. The Capella system is relatively close, at only 42.9 light-years (13.2 pc) from the Sun.
Although it appears to be a single star to the naked eye, Capella is actually a system of four stars in two binary pairs. The first pair consists of two bright yellow giant stars, both of which are around 2.5 times as massive as the Sun. They have exhausted their core hydrogen, and cooled and swollen, moving off the main sequence. Designated Capella Aa and Capella Ab, they are in a very tight circular orbit some 0.76 astronomical units (au) apart, and orbit each other every 104 days. Capella Aa is the cooler and more luminous of the two with spectral class K0III; it is 78.7 ± 4.2 times the Sun's luminosity and 11.98 ± 0.57 times its radius.
An ageing red clump star, Capella Aa is fusing helium to carbon and oxygen in its core. Ab is slightly smaller and hotter and of spectral class G1III; it is 72.7 ± 3.6 times as luminous as the Sun and 8.83 ± 0.33 times its radius. It is in the Hertzsprung gap, corresponding to a brief subgiant evolutionary phase as it expands and cools to become a red giant. The Capella system is one of the brightest sources of X-rays in the sky, thought to come primarily from the corona of the more massive giant. The second pair, around 10,000 au from the first, consists of two faint, small and relatively cool red dwarfs. They are designated Capella H and Capella L. Several other stars in the same visual field have been catalogued as companions but are physically unrelated.
This recording reflects the Wikipedia text as of 00:11 UTC on Wednesday, 21 March 2018.
For the full current version of the article, go to http://en.wikipedia.org/wiki/Capella.
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