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Moon, Saturn, and Antares

August 22, 2015

Almost from the day it’s born, a star is on a constant weight-loss plan. It blows some of the hot gas on its surface out into space in a steady “wind.” The Sun, for example, expels enough material to make a body as massive as Earth every 150 million years.

For some stars, though, the wind is much more furious. An example is Antares, the bright orange star at the heart of Scorpius, the scorpion. It expels enough material to make an Earth-mass body in just a couple of years.

The main reason for the difference is the star’s size. Antares is hundreds of times wider than the Sun. Since the star’s surface is a long way from its core, the surface gravity is much weaker than the Sun’s. That makes it easier for material to escape. And the surface area of Antares is roughly a half-million times greater than the Sun’s, so gas is streaming into space from a much larger region.

The combination creates a thick nebula around Antares. It’s lumpy, indicating that Antares blows more material into space at some times than at others. And a hot, bright companion star stirs up the nebula and creates a big structure that looks like an open umbrella. So the space around Antares is busy and turbulent — the result of the star’s own weight-loss plan.

And Antares is in good view this evening. It stands to the lower left of the Moon. The golden planet Saturn is closer to the Moon’s lower right — completing a beautiful triangle in the evening sky.


Script by Damond Benningfield, Copyright 2015

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