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Measure the Sky

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Week of Sept. 28 — Oct. 4, 2014

It was a cool, crisp Pennsylvania day in the autumn of 1966, and I remember it clearly. There I sat in Mrs. Moyer's 10th grade geometry class daydreaming out the window, as I often did, pondering everything except acute angles, midpoints and spheres.

"After all," I reasoned, "what use is knowing that a circle can be broken into 360 equal parts, each one degree wide. I've got better things to think about!"

Well, I'm embarrassed to say that this scene played itself out daily while I was in school. The irony is that out that very window existed circles that I would use just about every day of my professional life.

We can't see them, of course, but the heavens contain two "great circles" that can help us define the position of any celestial object.

The easiest to imagine is the one we know as the horizon. Starting at due north, scan your gaze eastward along the horizon and divide it into 360 equal pieces. One degree is approximately the width of your little finger held at arm's length; your fist — from thumb to little finger — also held at arm's length spans about ten degrees.

We always measure azimuth eastward along the horizon from true north. So, for example, something that lies due east is said to have an azimuth of 90 degrees east of north. And something in the north-northwest might have an azimuth of 315 degrees east of north.

Try this next time you're outdoors, and you'll find you've got an instant ruler on which to measure a celestial object's azimuth.

It provides a more precise way of describing directions than such broad terms such as "south" or "northeast."

There's another great circle that we can imagine; this one begins at any point on the horizon, passes directly overhead (the zenith) and continues down to the opposite side of the horizon. Since it's technically only half a circle, we can divide it into 180 degrees, and use it to measure the altitude of any celestial object. You can use your fist for this as well.

Check it out with the Polaris, the North Star, which remains relatively fixed in our sky. If you live in San Diego, for example, you'll find that the altitude of Polaris is about 33 degrees, while from the New York City area Polaris appears about 41 degrees above the horizon. That's because the altitude of the North Star conveniently equals your latitude.

There are other "great circles" in the heavens as well: the ecliptic, the meridian, the celestial equator ... and knowing these help astronomers grasp the layout and movement of our starry night sky.

It was back in the autumn of '66 that something clicked inside of me. Perhaps it was a clonk on the head during football practice; more likely, though, it was the skill of my geometry teacher who never gave up on that goofy kid in the third row.

Soon I became fascinated by how one can measure the world and universe with geometrical figures and angles, and how important this was to astronomers.

And for that gift, Mrs. Moyer, I thank you ... beyond all measure!

Visit Dennis Mammana at www.dennismammana.com. To read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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