Looking Up: Backup Is Just A Wobble Away

Oct 14, 2019

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This week on Looking Up Hal goes to Plan B, which is always good to have if you're heading into outer space.

I don’t know about you, but I like to have backups for things in my life. I carry an extra pen, and I like to have a backup plan if I’m going out. So, it seems reasonable that we have a backup north star, or pole star.

Well, it turns out, we have a backup for Polaris, in the dim but interesting star Yildun, which stays up in the night sky for everyone in the northern hemisphere.

As stars go, Yildun is not especially exciting. It’s an ordinary main sequence – or regular- star, though it does have a very rapid rate of spin. It takes 28 days for our Sun to turn once on its axis, while Yildun, spinning at just under 400,000 mph, only takes 19 hours to spin once. But it is the location of Yildun that makes it more interesting. If we didn’t have Polaris, we’d likely be using Yildun as our north star – it’s only 3.5 degrees away from the true north pole. But that is changing. Because the Earth wobbles on its axis, with a wobble period of 26,000 years, Yildun is slowing but surely wobbling away from the true pole. But don’t worry, in about 26,000 years, it will be right back to where it is, and it can be our back up pole star again.

If you’d like to take a closer look at Yildun, or any of the other wonderful and amazing things in the sky, please visit KRCC.org for a link to information on our monthly meetings and our free public star parties.