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SYFY WIRE Bad Astronomy

I Got It! Video of the Moon Occulting Venus.

By Phil Plait

Persistence pays off: Despite thick clouds in the morning preventing me from seeing the Moon occult (pass directly in front of) Venus, a little more than an hour later I was able to catch Venus reappearing from behind the Moon … and I got it on video!

I wrote about all this earlier. In a nutshell, as the Moon orbits the Earth it sometimes passes directly in front of other objects in the sky. This includes, rarely, the planets. On Monday at around 16:30 UTC the Moon passed in front of Venus.

Like I said, I missed that part due to clouds. But the Moon keeps orbiting the Earth, and shortly after 18:00 UTC (11:00 local time) it had moved across its own width, so Venus popped out on the other side. Happily, the clouds were only patchy, and I was able to catch it.

Actually, “popped” might not be the best word. Venus is about 16 arcseconds across (that’s an angular size; for comparison the Moon is about 1,800 arcseconds in size on the sky, much larger than Venus). The Moon moves roughly 0.5 arcseconds across the sky for every second of time, so it took 30 or so seconds for it to clear Venus. Venus actually fades in more than pops. Complicating this a bit, Venus is half full, so really it only took about 15 seconds for it to uncover the illuminated part of the planet. You can see this in the video if you look carefully; Venus gradually gets brighter over a few seconds.

Despite the cold and clouds, that was fun! I did a live Periscope stream for the September 2015 lunar eclipse, too, and that really worked out well. I’ll have to do more of this in the future. Hopefully the weather will cooperate! And for those asking: I used my iPhone hooked up to a Celestron Regal M2 80ED spotting ‘scope. If you’re looking for a really nice gift for someone for the holidays, I recommend it. It’s great for birdwatching and light enough to carry around on a hike or on travel. I really like using mine.

(Disclosure: Celestron sponsors my Science Getaways company, but the reason I asked them to do so is because I honestly like their equipment. If I didn’t, I wouldn’t recommend them.)

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