What’s Up With Those White Streaks Across the Sky? And What Causes Contrails, Anyhow?
Hey Mom,
The white streaks behind the planes that fly high? What are they? I think that you will know. Thank you for the answering of the question,
Streaking Towards Certainty
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Hey Blaze,
As long as that’s all the streaking you’re doing, I don’t think we’re going to have a problem. The white streaks following the airplanes you’re watching are called contrails, which is a fairly straightforward conjunction of the word condensation mashed up against trail. They aren’t exactly jet exhaust, but are a byproduct of the combustion of jet fuel. How so? As a jet engine burns fuel, it emits water, CO2, and particulates various and sundry that act as condensation nuclei.
As we all remember from high school science class, the atmosphere becomes colder with altitude, to the tune of an average of 2 degrees Celsius per thousand feet. The other thing I hope you remember from science class is that as the air becomes colder, it can hold less water vapor. Remember our old friend Bernoulli? Here he comes again with a third fascinating factoid from your school days having to do with the drop in temperature we can expect with a drop in pressure, which we’ll see whenever air gets moving faster. (Aren’t you glad you were paying attention to old Mrs. or Mr. So and So all those years ago? That stuff really DID finally come in handy!) Bring all of this together and what do you see? The water vapor introduced to the atmosphere due to jet exhaust is condensing into visible form due to the very cold temperatures and the associated inability of the atmosphere to hold that much water vapor in gaseous form, aided of course, by the condensation nuclei present in that exhaust.
Whew! Now go write a thank you note to your long suffering secondary teacher, already, who told you all that in the first place!
Mom
P.S. And while we’re at it, here’s your extra credit question: Why is the sky blue? Do you remember? We went over this one a couple of months ago…
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You’ve got questions? I’ll find you an answer. Email your aviation related question to mom@myskymom.com and check out myskymom.com to read the answers to questions previously posted. An educated pilot is a safe pilot is a happy pilot. Read on, fly safe, and remember: the only stupid question is the one you didn’t ask!
