Sunday, August 12, 2012

Perseus and the Perseids

In a literal sense we live in an age of enlightenment—meaning that the lights of cities are so bright that they make the night-sky almost invisible. The sky was clear last night. We saw faint glimmers—but street lights reflecting off the high branches of trees and the general luminosity of very near Detroit diminished hopes of seeing the Perseids, meteor showers named after the sons of Perseus. Perseus? The Greeks are still with us, even looking up at the sky. He was the son of Zeus and of the mortal lady, Danaë. His name is less generally recognized than that of the monster lady that he slew, the Medusa. To look at her turned you turn to stone, but looking at her in a mirror didn’t have the same effect. Perseus, therefore, holding a bright shield Athena had given him, approached the Medusa and made an end of her. This story greatly pleased the ancient Greeks—so much so that looking at the sky they could see the outlines of his form. Here is one version of the Perseus constellation:



He is holding Medusa’s head in the crook of one arm, his sword in the other. I have this figure from Wikipedia (link).

Now once every year, peaking at around this time, the northern skies are marked by a meteor shower. They are named after Perseus’ sons because the meteors arrive as if from the direction of the constellation. They come from a cloud of rocky debris that coincides with the orbit of a periodic comet, the Swift-Tuttle (130-year period). The cloud is thought to be debris left behind by the comet at least 2000 years ago, but a new filament appears to have been added late in the nineteenth century. So now we’re in the same neighborhood again, and those lucky to live deep in the country—thus about 50+ miles from a city—will see a portion of the wealth of rock bestowed on us by the Swift-Tuttle drawing swift bright lines in the skies above.

Being unable to see much, I thought I’d compensate by learning how to find the constellation next time we are really, really out of town. The following illustration (modified from telescoping.com, link) will do the job.


Find the big dipper and then use its more tilted side to locate Polaris. From there, follow roughly the same angle that brought you, going down again, you will find it pointing at Perseus’ head. For legibility, I’ve turned this image so that north is toward the bottom. A little bonus in staring at these lines comes from the realization that the Big Dipper forms the chest portion of the much greater Big Bear.

One of our happier books is Skywatching, published by The Nature Company and Time Life Books, 1994. It compensates for our excessively enlightened skies. Wonderfully illustrated. And it has yet to fail me in running down meaningful explanations and illustrations in gorgeous colors, artfully fusing myth and astronomy.

4 comments:

  1. Living in the heart of Paris I was quite surprised on Friday evening to see TWO shooting stars out my back window! I had come back from the café where I'd watched with my brother-in-law, sometime handballer, the last ten minutes of the men's handball semi-final which the French won: cocorico! We were looking out the back window, having a last cigarette and - Yes! - there they were: two shooting stars and the Big Dipper! But Paris has an energy policy of turning street lights down toward the street and leaving larger and larger portions of street in the darkness. I notice this coming home on my bike late in the evening.

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  2. We've enjoyed the handball games here as well, seen for the first time in this Olympics. Fun to watch. I like the fact that you can see the stars in Paris late at night--but not sure that it makes the city safer to dim the lights... These choices, choices...

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  3. We saw some pretty good ones on Wolverine Lake, where we got a fortunate two-hour break in the weekend's clouds on Saturday night. Two or three in particular were good fireballs with a long trail behind.

    I've read a lot of articles on light pollution. The most interesting thing is that lighting that doesn't clutter the night sky is generally cheaper and more effective because it focuses its light down on the ground where people are, and by not creating as much glare it also greatly softens darkness found in the shadows.

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  4. Rather like the notion, John, that a reasonable middle-ground exists: decent lighting and access to the skies at the same time...

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