The Moon-Aldebaran Occultation

Hey, everyone! I don’t have a ton of time to write today; it’s platelet donation day! So, I need to split pretty soon to get to that.

It might be a little bit of late notice for this, but there’s something going on in the skies tonight you might want to check out. Depending on where you are, it’s actually early tomorrow morning, so you’ll need be up late, or get up early, for it.

As you’ve probably noticed, some of the things I love most about watching the sky is to be able to see the universe in action. Most things that happen in the skies and happen in the universe, happen to slowly on a human scale that it’s hard to see any of it going on. Once in a while, though, we get treated to a moment or two when things happen more at our speed, thank you very much.

If you’re in the southern and eastern part of the US, late tonight early tomorrow morning, you’ll be able to see the Moon, now a waning gibbous, occult, block out, the orange giant star Aldebaran;  the brightest start in the constellation Taurus and the 14th brightest in Earth’s skies. The fun starts a bit after 1:00 A.M. October 19 Eastern / 12:00 A.M. Central / 11:00 P.M. October 18 Mountain / 10:00 P.M. Pacific. You’ll see the Moon slowly pass in front of Aldebaran, hide it, and then about an hour later it’ll reappear.

moon-ald-1230
The Moon will occult Aldebaran, October 19, 2016 (screens from Stellarium)

It’s the same sort of thing that happens when there’s an eclipse. In a solar eclipse, the Moon passes between the Sun and Earth, and blocks it out from our point of view. This time, the Moon will be passing between the Earth and Aldebaran from our perspective. Since Aldebaran is 65 light years away (figure, like, 380 trillion miles or 615 trillion kilometers) the effect is much more subtle, less spectacular. Even though Aldebaran is a giant star, much bigger than our Sun, the Moon appears from here to positively huge compared to it. After all, the Moon is only 239,000 miles away, on average. Much closer, so it looks much bigger. It’s like a mouse blocking out a tremendously far away elephant.

Remember, this is just how we see things from Earth. Both the Moon and Aldebaran are just going about their day. As with most things in life, perspective is everything.

As an added bonus, you’ll get to see the V-shaped Hyades cluster, which is the closest star cluster to Earth. Aldebaran looks to be part of the cluster, but it’s not. The cluster is actually about 100 light years further. The cluster, along with the constellation Taurus, are usually thought of as winter stars, but they’re starting to make their way into the evening’s skies these days. Before we know it, Aldebaran will be up with the rest of the stars in the Winter Circle just after dark easier to see. For now, this’ll have to do. Patience, my friends.

There’s been a series of these Moon-Aldebaran occultations going on for about the last year and a half, going back to the beginning of 2015, and they’ll continue into 2018, so catch them while you can.

Here’s quite a bit more from Sky & Telescope, including times, maps, and more about what’s going to happen. I hope you get to see this one. I plan to get up for it. Enjoy, everyone!

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