Intro to Constellation (4) Centaurus

A fascinating constellation, Centaurus.

Name: Centaurus

Abbr: Cen

Chinese Name: 半人马座

Brightest Star: Alpha Centauri (-0.27 m)

Visibility: 25 N to 90 S, prime in May

Centaurus is a bright constellation in the southern celestial hemisphere. There are 281 stars that are brighter than 6.5 magnitude (naked-eye visibility limit). In Greek mythology, Centaurus is the symbol of a centaur, a creature that is a half human, half horse. One can find many interesting stars in this constellation.

At the beginning of human civilization, Centaurus was a constellation located at the celestial equator. But for now, to observe all the stars in it, one has to go to the south of 25°N.

For Chinese astronomers, the constellation consists of stars in the following regions: 东方青龙，南方朱雀，近南极星区. Guangqi Xu (徐光启) completed the star chart of Centaurus.

Notable Stars

4.4 light-years away, Alpha Centauri is the closest star system to the Sun. It is a triple star system composed of a binary system orbited by Proxima Centauri, the closest star to the Sun at the moment.

The binary system consists of Alpha Centauri A and Alpha Centauri B. Both stars resemble the Sun in the sense of luminosity and mass. To the naked eye, the two primary stars appear to be a single star. The apparent single star is the third brightest star in the night sky.

The elliptical orbit of the two stars is eccentric. Their distance varies from 35.6 AU (Approx. Pluto to the Sun) to 11.2 AU (Approx. Saturn to the Sun).

The companion of the two-star system is Proxima Centauri. The Scottish astronomer Robert Innes discovered this star in 1915. 4.2465 light-years away, it is currently the closest star to the Sun.

Proxima Centauri is a faint red dwarf with an absolute magnitude of 15.6, over 20,000 times fainter than the Sun. Although its average luminosity is low, as a flare star, it sometimes undergoes dramatic increases in brightness because of magnetic activity.

Two planets have been detected and confirmed in orbit around Proxima. Proxima Centauri b is a planet within the habitable zone close to the size of the Earth. Proxima Centauri d is a sub-earth with a weight 0.26 times the Earth’s mass.

(Anecdote in Chinese)

Alpha Centauri是南门二，一个着实有趣的恒星系统。在刘慈欣的小说《三体》中，三体人居住的地方即是南门二附近。而在《流浪地球》中，人类的目的地也是南门二。电影《阿凡达》中，潘多拉星同样在南门二之中，环绕Alpha Centauri A。NASA曾在2017年宣布，他们会在2069年向南门二发射一个航天器。

Notable Systems And Objects

Omega Centauri or NGC 5139, is the largest and brightest globular cluster in the Miky Way. It’s 17,000 light-years away with a diameter of 150 light-years. NGC 5139 has a magnitude of 3.7. To the naked eye, it appears fuzzy and non-circular.

NGC 3918 is a planetary nebula known as the Blue Planetary. It was discovered by John Herschel and named for its color’s similarity to Uranus.

NGC 4622 is a face-on spiral galaxy with a prominent ring structure.

Credit

Most of the contents are summarized from Wikipedia. You can click the images to reach the source websites.