Astrophoto: Incredibly Thin Crescent Moon in Record-Breaking Shot

Bad Astronomy
The entire universe in blog form
July 9 2013 8:00 AM

The Newest New Moon

Thierry Legault photo of the crescent Moon
Sunrise on the Moon

Photo by Thierry Legault, used by permission

The picture above is likely the newest new Moon you’ll see: The crescent above is actually a record-breaker; the thinnest crescent Moon ever photographed!

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!  

It was taken by the astrophotographer Thierry Legault, who (as oxymoronic as it is) routinely takes extraordinary photos. He shot it from his backyard near Paris on Monday at 07:14 UTC, when the Moon was a mere 4.4 degrees from the Sun. For comparison, the Sun and Moon are about the same size in the sky, just 0.5 degrees in diameter.

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The geometry of this is interesting. Back in 2010, Legault took a similar shot when the Moon was a wee bit farther from the Sun, and I explained it all then if you want details. But in a nutshell, the Moon’s orbit is tilted a bit with respect to Earth’s, so it doesn’t pass directly in front of the Sun every orbit (which is why we don’t get a solar eclipse every month). Depending on the geometry at new Moon, it slides near the Sun, though never getting more than about 5 degrees away.

Therefore, at one particular moment, in the sky the Moon will be as near the Sun as it can get for that particular month. It was at that moment that Legault took the picture above. He got the timing to within a minute of the actual moment of newest Moon, so only the thinnest slice of the lit lunar landscape was visible from Earth.

As a reference, here is how much of the Moon was lit at that time:

Phase of the Moon
The thin white line: The phase of the Moon, with a teeny sliver lit, when Legault took his photo.

Photo by USNO

I got that from the U. S. Naval Observatory, and shows the current phase of the Moon. You can see that the vast majority of the Moon was dark, with only the narrowest sliver lit at the top. (I rotated the image to match the actual photo.) Legault had to use a computer-programmed telescope to find it at all.

Because the Moon was so faint and the Sun (and sky around it) so bright, he set up a piece of wood with a small circular hole in it to cut down on sky glare and used a near-infrared filter, where the sky is even fainter. Even so, this was an incredibly difficult shot to take, and he deserves kudos for it. For the record, I’ll note the Moon can get even closer to the Sun than this, making for an even more difficult picture. But if anyone is up to the task to snap that and break this current record, it’s Thierry!

Related Posts (featuring Legault's work):

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