Delta Scorpii

StarDate: July 28, 2009

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When you step out under a dark sky, one of the first things you notice about the stars is the twinkling. This rapid-fire change in brightness and color is caused by Earth's atmosphere -- an ocean of air that bends and splits the starlight.

But a star can actually do some "twinkling" on its own -- it just takes a while.

An example is Delta Scorpii, one of three stars that represent the head of the celestial scorpion. It's in the south at nightfall, to the right of Scorpius's "heart," bright orange Antares.

Delta Scorpii is a system of perhaps four stars. The brightest of the bunch is much hotter, brighter, and more massive than the Sun. Even from its distance of about 400 light-years, it's quite easy to see.

But over the last decade, the star has sometimes grown even easier to see. At times, in fact, it's about twice as bright as normal.

That's because Delta Scorpii spins on its axis almost a hundred times faster than the Sun does. That makes the star bulge outward at the equator, so instead of a ball, it's shaped more like a pumpkin.

Sometimes, this high-speed rotation flings hot gas into space. The gas forms a glowing disk around the star, making it appear brighter. Over time, the disk cools and fades. But then another eruption makes it brighter again. So Delta Scorpii produces its own brand of "twinkling" -- the kind that takes not seconds, but months or even years.

We'll talk about another star in Scorpius tomorrow.

Script by Damond Benningfield, Copyright 2009

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