Shower Predicted; Umbrella Not Necessary

By David Spector Gazette Contributing Writer

At this time of year, I expect an email from my father reminding me that the Perseid meteor shower peaks on the night of August 13. My father remembers watching a spectacular meteor shower, perhaps the Perseids, from a dark beach with his own father in the 1930s, and he continues to share the memory of that experience through these annual reminders.

The terms “meteor,” “meteoroid” and “meteorite” can be confusing. A meteor is the visible path of heated air made by a piece of extraterrestrial rock or ice (a meteoroid) encountering the earth’s atmosphere. Most meteoroids are dispersed in the upper atmosphere as vapor and dust; the small minority that reach the earth’s surface are called meteorites. A meteor shower happens when the earth passes through a swarm of debris. The Perseid shower occurs as the earth crosses the path of Comet Swift-Tuttle, which sheds bits of itself as it orbits the sun about once every 133 years.

Because the greatest activity of this year’s Perseid meteor shower coincides with the full moon, only the very brightest of the meteors will be visible then. Fortunately, this shower occurs over a long period, and at least a few meteors associated with it might be seen for about four weeks before and about two weeks after peak activity. Thus, if you look up for a few minutes or more on any clear night over the next few weeks—especially if you’re away from the light pollution of cities—you could sight one meteor, or many. If it appears to move away from the constellation Perseus in the northern sky, it is probably part of the Perseid shower.

Why, beyond the beauty of the show, should two biologists—my father and I—care about an astronomical phenomenon? A meteor shower gives a glimpse of processes that were essential in the history of life. The earth itself formed through the accretion of smaller objects, and Comet Swift-Tuttle and its trail of dust represent the type of material that originally built our planet. Indeed, each meteoroid, with its small bit of material added to the earth, continues that process of accretion. The gases, dust, comets and asteroids that came together to form earth provided carbon and the other elements necessary for life. The delivery from space of organic molecules, seen today both in distant dust clouds and in meteorites, provided some of the chemical building blocks from which life formed.

Life has had another, less pleasant, relationship with extraterrestrial bodies. The impact of an asteroid is thought to have caused drastic global environmental changes that resulted in the extinction of the non-bird dinosaurs and many other animal groups approximately 65 million years ago. The small objects in the Perseid meteor shower, even the very few that reach the earth’s surface, cannot cause such devastation, although the extremely unlikely collision with their parent body, Comet Swift-Tuttle, could be catastrophic.

Centuries ago a meteor shower might have been a disquieting indication that the firmament was not so firm. To me a meteor shower is an opportunity to appreciate processes happening across multiple scales of space and time. While the sizes of individual meteoroids might range from sand grains to pieces of gravel, each particle has been following an orbit that took it from the vicinity of Pluto to the upper atmosphere above me. The second or less that a typical meteor is visible contrasts with the roughly 4.5 billion years that the meteoroid had been part of the solar system. The brief flash of light shows in miniature both the processes that formed the earth and the kind of event that can produce mass extinction. On a personal scale, each meteor shower I see links three generations of meteor-watchers—my grandfather, my father and me—over eight decades.

 

Can one see, as William Blake suggested, “a world in a grain of sand”? In the fiery destruction of a sand grain overhead I can see parts of the history of this world and of my family. I hope you have a chance this month to look up, see some of these meteors and think about the histories they represent.

David Spector is a former board president of the Hitchcock Center for the Environment and teaches biology at Central Connecticut State University.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.

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