Volume XVII, Issue 39 # September 24 - September 30, 2009

Sky Watch

by J. Alex Knoll

The Star of the Sea

Dim Nunki burns with a fury

The moon waxes to first-quarter on the 26th, when it hovers above the spout of the Sagittarius Teapot. Look less than two degrees south for the bluish star Nunki, which at magnitude 2 shines bright amid the dim constellations of autumn. While there are no singly brilliant stars in this region of the heavens, it is the center of our galaxy and one of the most densely populated, riddled with countless stars, clusters and nebulae.

At the dawn of civilization, Nunki was the Sumerian god of water and the Star of the Proclamation of the Sea. Marking the center of the Milky Way, it is both a sea of stars and the home to the water-based constellations Aquarius, Capricorn, Delphinus, Pisces and Piscis Australis.

Nunki is one of the 100 brightest stars seen from Earth, but at 225 light years away, this star’s true luster has worn thin by the time its light reaches our eyes. With a diameter roughly eight times that of the sun and burning more than three times as hot, Nunki is no small fry. In place of our sun, it would appear 630 times brighter, but because it emits much of its light in the ultraviolet spectrum, Nunki is some 3,000 times as luminous as the sun. Were it the center of our solar system, life as we know it on Earth would be toast, while the planetoid Pluto and beyond would receive enough heat and light to sustain us.

For a star associated with water, Nunki burns with fury. Astronomers classify it as a blue-white subgiant — a massive, twin-fueled hybrid of sorts. Deep in its core, hydrogen is fused into helium, which the star consumes as a second course. All this fuel burns so fast that Nunki cannot survive forever and will eventually collapse into a white dwarf.

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