The Moon and Aldebaran

Hey, sky fans. It’s an exciting 24 hours or so overhead, so if you have a chance to take a look, you’ll be rewarded. I’m going to split these two things into separate posts to make the reading easier and shorter. Thanks for reading. I’ll post the second one later today or in the evening.

First, when you look at the sky this evening, you’ll see big waxing gibbous moon screaming its way through the constellation Taurus, and across the Hyades star cluster. If you’ve been keeping score, you’ll remember that I’ve mentioned the moon has picked up a hobby of occulting — blocking, passing in front of — the big, bright orange giant star Aldebaran in recent months. In fact, the moon is pretty much always blocking out something. Aldebaran is the brightest star along the way; the brightest one the moon can occult (other than the sun, of course, but solar eclipses are a different show).

Turns out we’re in the middle of a set of 49 of these stretching off into 2018. There’ll be 13 Moon-Aldebaran occultations in 2016 — one for each lunar cycle. Some of these occultations happen during the day, and some happen at wrong vantage point as seen from this place or that on Earth and can’t be seen. Tonight, though, across most of the US, Canada and a small part of Europe (as well as the open Atlantic), you’re in for a treat.

The time for where you live will vary. I’ll try to put together a list of times, but it’s probably best if you check the skies once darkness falls and keep an eye on the moon. Just before 9:30pm Eastern tonight where I live the moon will pass in front of Aldebaran. Aldebaran will disappear behind the moon’s darkened limb, and it’ll reappear from off its bright limb an hour or so later. Remember, this is just an optical illusion. Aldebaran is 65 light years away; so, it’s safely stationed like a billion and a half times further than moon, which is about 1.5 light *seconds* away. There’s no actual crashing or anything catastrophic happening here — no need to hide the kids and cats in your underground bunker. What you’re seeing, is mostly the effect of parallax. It’s like when you’re driving along, singing a song, and you see the trees just off the side of the road passing very quickly in front you while those off in the distance seem to hardly move at all. Now and again, one of the near trees blocks out one of the far-off trees. This is the same thing, but tremendously bigger, and overwhelmingly farther away.

This screenshot (from Stellarium) shows the sky to the southeast at around 9:30pm tonight from my corner of the world. The first one shows the always-gorgeous, and personal favorite, Orion-Taurus neighborhood, with the Pleiades cluster off to the right, and Orion to the left. There’s the moon sort of in the middle about to clobber Aldebaran.

moon 1
The southeast sky at around 9:30 tonight with the Moon about to occult Aldebaran (screen capture from Stellarium)

Since everything in the sky so often happens so slowly, this is a great chance to actually *SEE* something happen, and see that everything is always moving; never standing still. If there’s no clouds, and you can brave the cold, it’d be worth checking out. I’ll be out there, lukewarm Guinness in hand. Clear skies, folks!

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