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The Bull’s Horns

March 18, 2013

The Moon passes close to the tip of one of the horns of Taurus this evening. It’ll slip within a few degrees of Zeta Tauri, the star that marks the bull’s eastern horn. The other horn, El Nath, will stand to their upper right as night falls.

Zeta Tauri is much larger, heavier, and hotter than the Sun. The combination also makes it much brighter than the Sun, so it’s easily visible even though it’s more than 400 light-years away.

A disk of gas and dust surrounds Zeta Tauri, blown into space from the star’s surface. The dust grains form as atoms in that thick stellar wind link together to form solid particles. They absorb some of the star’s light. As they do so they warm up, so they emit their own glow, in the infrared.

El Nath looks brighter than Zeta Tauri, but that’s because it’s only about a third as far as the bull’s other horn. In fact, El Nath is only a few percent as bright as Zeta Tauri. It, too, is bigger and more massive than the Sun, but not as big as Zeta Tauri.

Both stars are nearing the ends of their lives. As they age, they will puff up to giant proportions and shine far brighter than they are now. Millions of years later, they’ll shed their outer layers, leaving behind only their dead cores, known as white dwarfs. Those stellar corpses will be as heavy as the Sun, but only as big as Earth. They’ll still shine because they’ll be extremely hot. But over the eons, they’ll radiate their heat into space, ending their days as dark cosmic ash.


Script by Damond Benningfield, Copyright 2013

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