The Moon Spits Out Saturn

The entire universe in blog form
May 18 2014 7:30 AM

The Moon Eats and Disgorges Saturn

Saturn and Moon
A composite image showing what Saturn and the Moon looked like in mid-occultation. Click to embiggen, and see the text below for an explanation.

Photo by Paul Stewart, used by permission

On the morning of May 14, 2014, the dance of the solar system brought together two unlikely partners: our Moon, and Saturn. As the Moon orbits the Earth, it makes a circle in the sky every month, and as Saturn orbits the Sun it too follows a circular but different path around our sky.

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!  

While these two tracks cross each other, it’s relatively rare for the Moon and Saturn to be at the same place at the same time. But it does happen, and it’s called an occultation. The Moon slowly covers Saturn, blocking it for some time, then once again moves out of the way to reveal the ringed planet. In this case, the timing of the May 14 occultation made it visible only for observers in the southern hemisphere, specifically Australia and New Zealand.


Photographer Colin Legg captured the moments when Saturn reappeared from behind the Moon, creating this video of the event:

I suspect a lot of people will be amazed at how big the Moon looks compared with Saturn, but I had the opposite experience! I’m used to the Moon looking big in my telescope, and Saturn small(ish). Seeing them right next to each other is a stark reminder of just how whopping huge Saturn is. It was more than 1.3 billion kilometers away during this event, while the Moon was only 380,000 kilometers distant!

Put it this way: Saturn was more than 3,000 times farther away than the Moon at the time. Like I said: Saturn is big.

Unfortunately, there are no lunar occultations of planets visible this year from the continental U.S. (Hawaii will see one of Saturn on Sept. 28), but don’t let that stop you from going outside and taking a look at the sky. Saturn is spectacular through a small telescope right now, and the Moon is always worth a gander. I’ll note the Moon is rising late at night as I write this; give it a week and you can see it in the east after sunrise. On the morning of Sunday, May 25, a very thin crescent Moon will be quite close to Venus, just a couple of degrees away! That should be very pretty.

And a note about the image at the top of this post: It’s by Paul Stewart, an amateur astronomer in New Zealand. It’s actually a composite of three images: A separate one each of Saturn and the Moon, which were cleaned up and then overlaid on an actual photo of the occultation as a guide. All three were taken minutes apart using the same equipment. So it’s not exactly real, but it’s not really fictional either. Saturn is faint compared with the Moon, so the shots of them together make them both look washed out (as you can see from the video). This image shows what it would look like if you could get everything balanced. I don’t think it’s that much different than putting together images from different telescopes (like Hubble and Herschel, for example) or seeing images taken in light our eyes can’t detect. Since Paul is open about how he did it, I’m OK with it too.

Tip o’ the dew shield to Suzy Webb and the Ice in Space Facebook page.

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


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