Friday, October 31, 2014

Partial Solar Eclipse

About a week ago, I was finally able to observe the second solar eclipse of my life – a partial eclipse with a maximum coverage of about 50%. The only other eclipse I have observed was another partial solar eclipse in May 2012.

A solar eclipse occurs when the moon casts its shadow on Earth's surface. From the point of view of an observer in the shadow, the moon covers the sun. It's not always obvious when a solar eclipse is happening; if the observer is in near the edge of the shadow, so the sun is only partly covered, it might not seem like anything unusual is happening.

This was my situation during the eclipse last week. The moon only covered part of the sun, so when I told one of my friends that an eclipse was occurring, he hadn't even realized it. And I don't blame him. Actually, a few minutes earlier, I hadn't realized it either. I got the time mixed up, and didn't think the eclipse had begun yet. The sunlight was weaker than usual, but I assumed that was due to the thin cloud cover. It wasn't until I looked up at the sun that I realized the eclipse had already started; although the sun was too bright to see the eclipse clearly, it left a temporary crescent-shaped mark in my vision.

Look familiar?
At first, I didn't want to try anything special. I just got a tiny piece of cardboard from a cereal box, and punched a small, round hole through it with the tip of a knife. Then I got a piece of white paper, and held the cardboard so its shadow fell on the paper. When I held the cardboard an arm's length away from the paper, the light falling through the hole made a crescent-shaped spot on the paper. This setup, called a "pinhole projector," is one of the simplest ways to view a solar eclipse.

Finally, though, I decided I wanted something better; my friend was visiting, and he hadn't seen an eclipse before. So I went into storage and pulled out the setup I had used for the previous eclipse. This time, though, the box was completely closed, with two holes: one for the telescope to project through, and the other for the observer to peek into the box. The inside of the box was spray-painted black, to reduce diffuse light scattering, and for the white area at the back of the box, I used a white piece of card-stock. The result was a much better projection of the sun. My friend was amazed at what he could see; a group of sunspots was even visible, right at the center of the crescent.

This eclipse was a fun experience. I had an opportunity to view an event I had only seen once before, and was able to give another person the same opportunity. There might not have been much to look at, but it was worth it just the same.

Next up: the total solar eclipse in 2017, when the moon will completely cover the sun. I'll be ready for it!

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