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In Dick Kreck's column Wednesday, Paula Erickson of the federal Earth Science Information Center settled one pressing question -- how much wider is Colorado at the bottom than the top? (30.9 miles if you missed it there.)
However, she said she had been asked the acceleration of
gravity at 5,280 feet above sea level, and she had no
idea.
I wanted to show off, so I delved into a standard
reference, the CRC Handbook of Chemistry and Physics.
The acceleration of gravity varies by both altitude and latitude. The earth is not a perfect sphere -- like me, it bulges in the middle. The farther you are from its center (that is, the closer you get to the equator), the less force from its gravity. The acceleration at 39° north of the equator is 32.1549 feet per second per second, and at 40°, 32.1578.
Denver is close to 40 degrees (Baseline Road in Boulder runs right along the 40th parallel, which also separates Nebraska from Kansas), but we need precision here. The World Almanac said Denver is at 39°44'58" north latitude.
Applying some linear interpolation -- back in 11th-grade trig, Mr. Springston said we would need that skill someday, and I'm pleased to report that the day has arrived -- I came up with 32.1571.
That's for mean sea level, though. The altitude adjustment is -0.000003086 for each foot above sea level, or -0.01629 for 5,280 feet. Thus in a city a mile above sea level at 39°44'58", the acceleration of gravity is 32.1408 feet per second per second.
Since this value determines the swinging time of a pendulum, it appears that you could use an old-fashioned clock as an altimeter. But I leave that exercise in hypsometry for some youngster's science-fair project.
I had other questions. Who decided that Denver is at precisely 39°44'58" north latitude and 104°59'22" west longitude? One second of arc is about 101 feet, so this means that there is a 10,201-square-foot parcel somewhere in the 111 square miles of Denver County that is the real Denver.
Where is that spot? Does it comprise the step on the
state capitol that is exactly a mile above sea level? It's
like highway signs. Once when I was on a Sunday ride with
my parents, I saw a sign that said Fort Collins 4,
even though the Fort Collins city limits were directly
ahead. asked How do they figure these distances?
My dad said he suspected they measured from post office to post office, but he wasn't sure. I still don't know.
Down here, when you turn off U.S. 285 onto Colo. 291, it
says Salida 10.
It's more like seven miles; if you
insist on driving 10, you're either on your way to
Cañon City, or you're cruising F Street with the
teenagers.
I just said down here.
But why? We're at 7,036
feet above sea level, 1,756 feet above Denver. We're
down,
though, since maps are usually oriented with
north up, which makes south down. But orienting
actually means to aim at the east, not the north, so how
can you orient to the north?
I don't know. Call the folks at the Earth Science Information Center. Or the Colorado Highway Department. Or the National Oceanic and Atmospheric Administration. No wonder kids don't want to study geography these days. You end up with more questions than answers.
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