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WeatherQuesting
with April Holladay

WonderQuest with April Holladay
— to solve science mysteries, your wonders.

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Interacting with nature by K:

How to Offer Wild Birds Shelter in the Winter

Not all birds migrate south for the winter.  Winter is a hard season for birds, and many risk freezing to death at night. It doesn't take much effort or money to provide shelter for them, and it can make a huge difference to the little feathered guys!

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Air thins on high

Ultra long duration balloon flies where the air is thin — above 99 % of Earth’s atmosphere. [NASA]Ultra long duration balloon flies where the air is thin — above 99 % of Earth’s atmosphere. Photo courtesy of NASA.

Q: Why does the air get thinner at high altitude? Katie, Oregon, Wisconsin

A: Air seems nebulous but is massive. Earth’s gravity pulls air molecules down, squeezing them together.

Air languishing at Earth’s surface has 200 miles of atmosphere piled above and a weight of 14.7 pounds (6.67 kg) on each square inch (6 square centimeters). At 18,000 feet high, the weight above halves and the air is twice as thin.  That's why the air gets thinner at higher altitude:  less mass above squeezes it less, so the air is less dense.

(Answered Feb. 6, 2004; updated Sep. 22, 2007)

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