Time lapse: When the Moon ate Venus

By Phil Plait | August 31, 2012 6:30 am

On the morning of August 13 – 14 (depending on where you were in the world) the Moon slipped directly in front of Venus in the sky, an event called an occultation. It was cloudy here in Boulder so I missed it, but halfway across the world in Korea, astrophotographer Kwon O Chul had a magnificent view, and made this lovely time lapse video of the event.

Occultations like this are relatively rare. If all the planets and moons orbited the Sun in exactly the same plane – that is, if you looked at the solar system from the side and all the orbits aligned perfectly, like looking at a DVD from the side – we’d see occultations all the time.

But in reality all the orbits are tilted a little bit. Venus circles the Sun in an orbit canted by about 3° compared to Earth’s. The Moon’s orbit is tilted by 5 °. The Moon orbits the Earth once per month or so, but it usually passes by Venus, missing it by a bit because the orbits aren’t aligned. But sometimes, every few years, the dance comes together, and the Moon wil slip directly in front of Venus.

An occultation is an amazing thing to see. I saw a lunar Venus occultation when I was a kid and just starting out as an amateur astronomer. It takes a few seconds for the Moon to cover a planet, so you can watch as the planet dims and then pops out when it gets completely covered. Also, the Moon commonly passes in front of stars, which are so far away and appear so small they just wink out, blip!

You can get a list of upcoming occultations at the International Occultation Timing Association website. If you get a chance to see the Moon occult a star, take it! Binoculars help a lot, and it’s fun to watch the star just suddenly blink out.

Tip o’ the dew shield to Astropixie.

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (19)

  1. KAE

    I remember taking part in an occultation timing with our local astronomical society. It was a star occultation by the moon and we had several telescopes stretched along a highway. Each of us had a button to press when we saw the star wink out and when it reappeared. Don’t remember the details of the central data collection equipment. This was in the mid to late 70’s. I often wonder if this is still done.

  2. Mike

    Fade to black…

  3. Hey Phil. That’s awesome.

    What stood out to me more was how incredible the moon looks from :23 – :29. It’s absolutely beautiful. Seeing the Moon 2/3rds dim and 1/3 completely illuminated by the Sun is so cool. It’s always* exactly 50% lit up by a beam that travels 93 million (+/- the radius of the Moon’s orbit from the Earth.) and sweeps across the surface at a rate equal to the Moon’s rotational period (+ whatever effect caused by the Earth’s orbit around the sun) From our angle we see the crescents and wedges as it rotates but half of it is always illuminated. We hardly ever get to see the dim side like this. Most people just see the range of crescent to full. The dim side is illuminated by sunlight bouncing off the Earth, correct?

    This video seems to be one of the best examples of the border of the Sun’s reach. Is there a term for that border? How would an astronaut experience the arrival of the sun? (‘sunrise’ is the technical term, I suppose.) He’d have to crank up the AC on his suit, no doubt. Did NASA ever make a suit that allowed an astronaut to survive in Moon night? Even with no atmosphere there must be some kind of gradient before full exposure? Or is it like a light switch? Surely the sun crests the Moon’s horizon at a static pace before being fully revealed. I love El Moon!

    Those who can’t moonwalk, moontalk. Keep up the great work, Phil.

    *except during eclipseseses

  4. Ben

    But the moon is bigger. Should it be behind Venus?

  5. But if Moon eats a bigger planet like the Earth-sized Venus its gunna burst! RUU-UUN! ūüėČ

    Seriously, great clip. Loved it. :-)

  6. Chris

    When the Moon ate Venus…
    then spit it out.

    Although it did come out from the opposite end, so perhaps spit is not the most accurate word ūüėÄ

  7. @ Hank Thompson

    The dim side is indeed illuminated by sunlight reflected by Earth, and it’s called Earthshine. The shape of the Earth as seen from the Moon is always the “opposite” (or complement) of the shape of the Moon as seen from Earth e.g. a full Moon means the Earth is “New” as seen from the Moon, and a small Lunar crescent means the Earth is almost full viewed from the Moon.
    The Earthshine is therefore best seen close to New Moon.

    The “border” between light and dark (sunrise from New Moon till Full, and sunset from Full Moon till New) is called the terminator (seriously). Any resemblence to movie titles featuring a former “Governator” is entirely coincidental.

    I don’t know if NASA made any lunar night suits, but the astronauts moved in and out of the Lunar Module’s shadow and did not seem to be affected by any temperature differences.

    Anyway, that movie is great!

    Greetings from the Netherlands. :)

  8. JR

    Hank Thompson, I believe the line separating darkness from light on a given body, albeit a planet, satellite, whathaveyou, is called the terminator. You might want to fact check some of your other statements regarding the moon’s illumination.

  9. Hermann

    Hmmm. When I observed this event Venus’ phase was not nearly as full as it appears in this video. I saw something more like waxing gibbous, around 2/3 full.

  10. Pete Jackson

    Observers on Venus (i.e. in the upper atmosphere above the cloud layer) would see the Moon (1/4 the Earth’s diameter) transiting the Earth, and with both disks mostly fully lit.

    The Moon would look much darker than the Earth (10% vs approximately 50% reflectance), and with the skinny portion of the moon which is between the terminator and the limb, and hence completely unlit, looking like a black crescent! Perhaps some artist out there can do a rendering…

  11. One Eyed Jack

    First Venus, then the Earth… nuke the moon before it eats us!

    Someone call Bruce Willis.

  12. Bruce

    I enjoyed the daytime view of this from Pomona, CA. It was pretty cool, but this guy got the better deal on this one.

  13. Chris

    @8 Pete Jackson
    If you have Stellarium (it’s free) you can change your location to Venus and observe it from a Venusian perspective. Kind of cool, thanks for the idea.

  14. Great video, thanks for posting. Living near Seattle and working nights I almost never get see sufficient like this.

  15. Peter B

    Ben @ #4 asked: “But the moon is bigger. Should it be behind Venus?”

    No. Because the Moon is always about 380,000 kilometres from the Earth, while Venus is always tens of millions of kilometres away. If Venus was ever closer to the Earth than the Moon was, we’d be in big trouble.

  16. Lee

    This is somewhat unrelated, but is it true real astronomers are not really that interested in blue moons because they are the result of a manmade adoption of the Gregorian calendar rather than an intrinsic phenomenon, such as the lunar occlusion of Venus?

    Not a huge deal, but I was nanosuprised when I didn’t see anything about it on your blog.

  17. VinceRN

    Lee @ 14 – I would think so. I’m only a very amateur astronomer and really have no interest in “blue moons” – though I did change the colors on a moon picture to blue and share it on my FB. “Blue Moon” doesn’t really mean anything except perhaps to point out that despite the etymological relationship our month has nothing to do with the lunar cycle. Still, it’s fun.

  18. Sparky

    Somehow, the two things that sprang to mind when watching the video (courtesy of cookie monster) were

    “Om nom nom nom.”


    “The moon also sometimes looks like a C, but you can’t eat that, so …”


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