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This Month: Find Centaurus and Omega Centauri Star Cluster (May 2018)

This Month: Find Centaurus and Omega Centauri Star Cluster (May 2018)

One constellation, which is only visible to a small extent from our northerly latitudes, is Centaurus, the Centaur, the half-man, half horse. Only the upper portion of Centaurus comes above our southern horizon between 10 p.m. and midnight in May.

Centaurus is one of two centaur-shaped constellations. The other is the zodiac sign Sagittarius. In addition to being one of 88 official modern constellations, Centaurus was also among the 48 ancient constellations listed by second-century astronomer, Ptolemy.  While Sagittarius is said to represent the learned centaur, Chiron, who served as tutor to such heroes as Hercules, Theseus, and Jason (of the Argonauts fame), Centaurus is simply a “generic” centaur.

centaurus half man, half horse diagram

69 stars make up the constellation Centaurus.

Centaurus’ Two Bright Stars

The constellation Centaurus contains 69 stars. Among them are two bright, first-magnitude stars (although we can’t see them): Alpha and Beta Centauri.

Alpha Centauri is a triple star system, famous as the nearest star to our Sun. It’s 4.34 light years away, or approximately 25 trillion miles. Of the three stars in this system, the two brightest are very much alike in size and luminosity, while the third star, Proxima Centauri ,is one of the least luminous of all known stars, and yet slightly closer to us than the bright pair.

To the upper right of Alpha is first magnitude Beta Centauri, itself a triple star system which has the proper name Hadar, and seems to be an apparent neighbor of Alpha. But hardly! In reality, Beta Centauri is 390 light years away; a bright blue star, ten times more massive than our sun and nearly 42,000 times more luminous!


NASA/Penn State University image

A Globular Star Cluster: Omega Centauri

One object in Centaurus that does come above our horizon is Omega Centauri, the finest example of a globular star cluster, and one of the most magnificent objects visible within range of telescopes. Unfortunately, from mid-northern latitudes, Omega at its best lies only a few degrees above the southern horizon and is almost always perpetually masked by a thick layer of haze that is usually present near and around the horizon.


With contributions from astronomer Joe Rao

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