Learn what to look for in the night sky with today's Nerdy Curio from Stardate. One of the highlights of a solar eclipse is the chance to see the corona — the Sun’s outer atmosphere. Its thin gas reaches millions of degrees, producing a faint, silvery glow around the Sun.

A corona also encircles the brightest star of Cetus, the sea monster. It’s even bigger and hotter than the Sun’s. But it may not be produced in the same way.

Beta Ceti is in the southwest at nightfall. It’s the second-brightest star in a wide swath of sky. It’s outshined only by Fomalhaut, which is quite low at that hour.

Beta Ceti is a giant — it’s almost 20 times wider than the Sun. It got that big after it ended its “normal” lifetime. It consumed the original hydrogen fuel in its core, converting it to helium. The core then got smaller and hotter, allowing it to begin fusing the helium to make heavier elements. The hotter core pushes on the outer layers of gas, causing the star to puff up to giant proportions.

About a decade ago, space telescopes discovered that Beta Ceti is producing a lot of X-rays. They come from the star’s corona.

The Sun’s corona is produced by a magnetic dynamo. Different layers of the Sun rotate at different rates, generating a magnetic field. It guides charged particles from the surface out into space, forming the corona.

Beta Ceti, though, probably has a weak dynamo. Instead, its magnetic field is at least partly a leftover from the star’s earlier life — a magnetic fossil that helps create a giant corona around this giant star.

Script by Damond Benningfield

Aired January 12, 2018

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