# Marilyn Miscalculates Earth's Rotational Velocity

Ask Marilyn ® by Marilyn vos Savant is a column in Parade Magazine, published by PARADE, 711 Third Avenue, New York, NY 10017, USA. According to Parade, Marilyn vos Savant is listed in the "Guinness Book of World Records Hall of Fame" for "Highest IQ."

In her Parade Magazine column of May 4, 1997, Marilyn reports a value of 1370 feet per second as the Earth's eastward rotational velocity at Cape Canaveral.

## Almost right

Phil Plait <badastro@badastronomy.com> directed me to his Bad Astronomy web site, which contained the following explanation of Marilyn's error:
That number (1370 feet per second) is wrong. At the Equator, the Earth spins at 1000 miles per hour (the Earth is 24,000 miles around, and spins once every 24 hours). This is 1467 feet per second. Now, as you move up in latitude that velocity decreases. Imagine standing at the North Pole; you are not moving at all, but simply spinning in place. The velocity changes with the cosine of your latitude. I looked up the latitude of Cape Canaveral, and it s 28.5 degrees North. The cosine of 28.5 = 0.88, so the rotation of the Earth at that point is 0.88 * 1467 = 1290 feet per second. Now, her number isn't really very far off, but it is incorrect. I wonder where she got it from? I am guessing she misread the latitude of Cape Canaveral off a map. The number she gets corresponds to a latitude of 21 degrees, which is 500 miles farther south.

According to Craig Gentry <gentry@law.harvard.edu>

Phil has indeed given you some "bad astronomy." The Earth is not 24,000 miles around at the equator; it's 24,901.55 miles around (according to my 1988 almanac, which I assume is still up to date in this respect.) This gives Cape Canaveral a rotational velocity of 1337 ft/s, a figure closer to Marilyn's than to Phil's.

But Phil is almost certainly right about Marilyn misreading the latitude (or punching it into her calculator wrong). If she used 25.8 degrees instead of 28.5, she would get 1370.07 ft/s.

http://www.wiskit.com/marilyn/launch.html last updated February 10, 1999 by herbw@wiskit.com