The Sciences

The Moon and Venus, sittin' in a tree

Bad AstronomyBy Phil PlaitFeb 28, 2009 4:02 PM


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Last night, the Moon and Venus passed each other in the sky, getting pretty close together -- about a degree apart, or twice the Moon's width. The Moon was a lovely thin crescent, and Venus shone brilliantly, making them a great target for astrophotos. I took a few dozen shots, but here is my favorite (click to embiggenate):

This was a three-second exposure I took around 6:15 p.m. local time. I love how you can see the unlit portion of the Moon... unlit by the Sun, that is. The reason you can see it is because it's being lit by the Earth; in the Moon's sky the Earth is as much as 50 times brighter than the full Moon. So that lunar landscape is actually reflecting that light back to you, though far dimmer than the sunlit surface. There are also two airplanes in the picture. One is easy, the other is hiding. See them both? You can see two dark smudges over my roof, too. Those are caused by dust and dirt on the digital detector inside my camera. I tried to clean it out the other day, taking the camera apart into about a dozen pieces, but couldn't dislodge them. Because they sit on the detector itself, they are wildly out of focus and look like big fuzzy blotches. This happens in astronomical detectors too, and there is a process (called flat fielding) to remove them. However, that's a lot of effort to undertake and I don't have the time or energy. I'm not all that gifted with Photoshop (which is obvious if you're a regular reader here), and I think removing them when the sky brightness has such a large gradient would be tedious. Still, the lesson here is that point-and-shoot cameras can take lovely photos. Here are two more; both taken after the one above (you can see how the Moon and Venus have set a little bit in the intervening time). The one on the left is also a three-second exposure, but taken later when the sky was darker. The one on the right is a 10 second exposure taken even later, but the longer exposure allowed the sky to look brighter. If you look carefully you can even see features on the "dark" portion of the Moon.

If you have a cheap digital camera and a tripod, you can take pictures like this, or even better. I really suggest you try. Orion is up high now right after sunset, and makes a perfect beginner's target, with lots of bright stars and a very recognizable pattern. Feel free to experiment: long exposures, short ones, different aperture settings, maybe even using a flash to illuminate nearby trees. When I was starting out in high school, I had to use film, which was expensive and took forever to process, so I was conservative when fooling around. Now with digital cameras, taking 40 pictures is as easy as taking one! It just costs time, and you might stumble on an idea that makes your picture really beautiful. Go! Take pictures!

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