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May 17, 2019

The eyes of the dragon shine a third of the way up the northeastern sky at nightfall now. Eltanin is the brightest star of Draco, with third-ranked Rastaban just above it. They circle high across the north during the night, and stand in the northwest at first light.

Although Eltanin looks brighter than Rastaban, it’s only because of their different distances. Eltanin is about 150 light-years away, while Rastaban is at 380 light-years. So if you lined them up side by side, Rastaban would shine several times brighter than the dragon’s other eye.

Rastaban is only about 65 million years old, compared to four and a half billion years for the Sun. Yet it’s already passed the end of its “normal” lifetime. That’s because it’s about six times as heavy as the Sun. Such massive stars “burn” through their nuclear fuel at a frantic rate. So Rastaban has already converted the hydrogen in its core to helium. Now, it’s probaby getting ready to ignite the helium to make carbon and oxygen.

That’s caused the star to puff up — it’s about 40 times the diameter of the Sun. That’s the main reason it looks so bright — there’s a lot of surface area to beam light out into space.

Eventually, the nuclear reactions in the core will stop. The star’s outer layers will puff out into space. That will leave only the dead core — a cosmic ember as heavy as the Sun but only as big as Earth — the final stage for one of the dragon’s bright eyes.

Script by Damond Benningfield

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