Astonishing Mira

An “astonishing” star should be at its best this month. The star puffs in and out like a beating heart, getting brighter and fainter with each beat. It’s in the “contraction” phase now, so it could reach its brightest around the middle of the month.

The star was noted 425 years ago today by David Fabricius. When he looked at it a couple of weeks later, it was noticeably brighter. But by a couple of months after that, the star had vanished.

Later, another astronomer figured out that the star brightens and fades every 11 months. And a third astronomer named it Mira — a Latin word meaning “astonishing” or “wonderful.”

Mira is at the end of its life. It’s a little heavier than the Sun, and much bigger. Its exact size varies by about 20 percent — from more than 300 times the Sun’s diameter to about four hundred.

That’s because the star is making a transition in the way it produces energy. That process is unstable, so the star has gotten a lot bigger. It’s also made the outer layers unstable, causing them to pulse in and out. When Mira is smallest, it’s also hottest, so it shines brightest.

And the star is headed toward that point in its cycle. That should make it an easy target — something we can’t always say about this “astonishing” star.

Mira is in Cetus, the sea monster. It climbs into good view by about 2 a.m., and is high in the sky at first light. It’ll rise earlier over the coming weeks, and stand due south at dawn.
 

Script by Damond Benningfield