Red Rock, Black Spider, Blue Moon

By Phil Plait

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Posted Tuesday, Aug. 27, 2013, at 10:15 AM

The allure of Uluru and the Moon. Click to downunderenate, and you want to.
Photo by Storm DiCostanzo, used by permission

Your word of the day is lunation.

This is the term given to a single cycle of the phases of the Moon, from new to full and back to new again. A lunation is about 29.5 days (think “moonth” if that helps). Each lunation is given a unique number—there are various systems, but the most common starts with the cycle that began in January 1923. In that case, as I write this, we’re in Lunation 1121.

This last full Moon was interesting. Some people were calling it a Blue Moon, which made me chuckle: The term has no scientific meaning but has a cultural one of being the second full Moon that occurs in a calendar month. However, that can’t be true in this case, since the full Moon was just after midnight on the evening of Aug. 20-21. If it takes nearly 30 days to go through a set of phases, the Blue Moon has to happen on the last couple of days of the month.

Some people say a Blue Moon is the fourth full Moon in a season, but even that is more folklore than anything else. The term really just means something very rare and was later adopted to pertain to the actual phase of the Moon. And it has nothing whatsoever to do with the color of the Moon. So there.

Still, because of the buzz, a lot of folks went out to look at the Moon (I tweeted about it, too—twice actually, the second one being a joke). A lot of people sent me pictures of it, and a couple from this current lunation were cool enough that I wanted to share.

The first (shown above) comes from my friend Storm DiCostanzo, aka “and Storm”, one half of the musical geek duo Paul and Storm. He and his wife happened to be in Australia at the same time I was recently, and we got together to spend an afternoon in Sydney. They told me they were going to Uluru, aka Ayers Rock, and I was jealous; I’ve always wanted to visit. But that jealousy increased hugely when I saw the amazing shot Storm took.

Uluru is a several-hundred-million-year-old sandstone inselberg (island rock) in central Australia. It’s difficult to get to and is incredibly isolated from cities. The skies there get substantially dark, though the nearly full Moon would bleach out the stars. Still, if it means getting a photo like Storm’s, then maybe that’s worth it.

The second shot is a bit more whimsical and was sent to me by Steve Marr (arachnophobes, you may want to skip this one):

This spider may've bitten off more than it can chew. [Alt.: We're gonna need a bigger web.]
Photo by Steve Marr, used by permission

This is actually what’s called a high-dynamic range or HDR picture. When you take a picture with your camera, it sees light linearly; that is, something twice as bright looks twice as bright in the picture. Our eyes don’t really see that way, though. It’s complicated, but overall we see logarithmically: Something twice as bright might only appear fractionally brighter to our eye. That’s why most pictures overexpose so quickly while our eyes see the same scene just fine.

HDR photography compensates for this a bit. The camera takes three exposures—one short, one medium, and one long—to be able to see bright, medium, and faint highlights. It then combines them into one shot that more closely mimics what the eye can see.

That’s what Marr did for this lunar arachnophilic picture. It also gives the picture a slightly creepier edge to it—like it really needs it.

We see the Moon almost every day, sometimes at night, sometimes during the day, sometimes full, sometimes new, and with every phase in between. It’s always changing, always different, and always lovely to behold. If you can, go take a look.