Very Cool Video of the Moon Passing Directly in Front of Jupiter

Bad Astronomy
The entire universe in blog form
Dec. 29 2012 8:00 AM

When the Moon Ate Jupiter

Still from the video of the Moon occulting Jupiter.
The Moon just about to pass directly in front of the planet Jupiter on Christmas Day.

Image credit: Rafael Tefavari.

As the Moon orbits the Earth, we see it sliding across the sky, making a complete circle once every month or so. Its motion is slow, almost invisible to the naked eye, though if you’re patient you can see it move very slowly relative to the stars in the sky. Sometimes, it actually passes directly in front of a bright star, an event called an occultation. Less frequently, things line up just so, and it occults something brighter, like a planet.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Last week, from North America, Jupiter and the Moon were very close to together; from my house in Boulder, Colorado they were less than a degree apart (roughly twice the width of the Moon on the sky). But from South America the angle was slightly different, and on Dec. 25, 2012, viewers there saw the Moon directly occult Jupiter.


Via I saw this video from astronomer Rafael Defavari, who was able to take video of the event through his Celestron 20 cm. telescope in Brazil!

That’s pretty cool. The video is sped up by a factor of five to show the process. At the end he also got a shot of Jupiter reappearing, with its moon Europa Io popping up just ahead of the planet. You can see the shadow of Europa Io on Jupiter’s cloud tops, too. Bear in mind, the Moon was about 400,000 km (240,000 miles) away at the time, but Jupiter was over 600 million kilometers (360 million miles) farther out! It looks small here, but in reality Jupiter is over 40 times wider than our Moon. [Update: My apologies; I originally misidentified the moon Io as Europa.]

I’ve seen a couple of occultations like this in the past. Unfortunately, there won’t be any good ones visible from the United States this coming year, but if you live in South America or Africa you’ll get lots of chances: the US Naval Observatory has a list of them coming up. Jupiter and the bright star Spica in Virgo get blocked by the Moon several times over the next few months, and you don’t need anything but your eyeballs to see them. If you have a decent-sized telescope, Pluto gets occulted by the Moon a few times as well. Those happen over the Northern Hemisphere, so check the list if you want to try for it—but you’ll need a good ‘scope and camera to detect faint Pluto, so it’s probably only an event for people who have some experience looking at such things.

You may be wondering why the Moon doesn’t block Jupiter (and every other planet) every time it orbits the Earth. It’s because the Moon’s orbit is tilted with respect to the plane of the solar system. The solar system is flat, so to us the planets appear to move around the Sun in a line on the sky called the ecliptic. But the Moon’s path is tilted, so it can only occult a planet when it crosses the ecliptic and a planet happens to be at that point. It’s a bit like safely crossing the street; you’re crossing the path that cars travel on, but as long as no cars are actually there when you cross you’re OK.

Most of the time that’s true for the Moon as well, but sometimes a planet is at that spot, and the Moon glides in front of it, blocking it. Because the Moon is big, and the planets move slowly, in general if you get an occultation one month, you get one or two more over the next couple of months. That's just what we're seeing here.

Unfortunately, from here in the States we don’t get to see these Jupiter occulations, but again, if you live south of the Equator, check the USNO site and see if you can watch one!



Smash and Grab

Will competitive Senate contests in Kansas and South Dakota lead to more late-breaking races in future elections?

Stop Panicking. America Is Now in Very Good Shape to Respond to the Ebola Crisis.

The 2014 Kansas City Royals Show the Value of Building a Mediocre Baseball Team

The GOP Won’t Win Any Black Votes With Its New “Willie Horton” Ad

Sleater-Kinney Was Once America’s Best Rock Band

Can it be again?


Forget Oculus Rift

This $25 cardboard box turns your phone into an incredibly fun virtual reality experience.

One of Putin’s Favorite Oligarchs Wants to Start an Orthodox Christian Fox News

These Companies in Japan Are More Than 1,000 Years Old

Trending News Channel
Oct. 20 2014 6:17 PM Watch Flashes of Lightning Created in a Lab  
  News & Politics
The World
Oct. 20 2014 1:50 PM Why We Shouldn’t Be Too Sure About the Supposed Deal to Return the Abducted Nigerian Schoolgirls
Oct. 20 2014 7:23 PM Chipotle’s Magical Burrito Empire Keeps Growing, Might Be Slowing
Dear Prudence
Oct. 20 2014 3:12 PM Terror Next Door Prudie advises a letter writer whose husband is dangerously, violently obsessed with the neighbors.
  Double X
The XX Factor
Oct. 20 2014 1:10 PM Women Are Still Losing Jobs for Getting Pregnant
  Slate Plus
Tv Club
Oct. 20 2014 7:15 AM The Slate Doctor Who Podcast: Episode 9 A spoiler-filled discussion of "Flatline."
Brow Beat
Oct. 20 2014 9:13 PM The Smart, Talented, and Utterly Hilarious Leslie Jones Is SNL’s Newest Cast Member
Future Tense
Oct. 20 2014 4:59 PM Canadian Town Cancels Outdoor Halloween Because Polar Bears
  Health & Science
Medical Examiner
Oct. 20 2014 11:46 AM Is Anybody Watching My Do-Gooding? The difference between being a hero and being an altruist.
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.