Simanaitis Says

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YESTERDAY’S CELEBRATION OF global—and extraglobal—adventurer Kathy Sullivan got me thinking about planet Earth and its physical extremes, its heights, depths, and shape. Here are tidbits gleaned from a variety of Internet sources. I offer one as something merely to ponder; that is to say, “it depends.”

This and following images from NASA’s Earth Observatory.

Earth as a Globe, Sort Of. Though we model the Earth as a globe, a sphere, it’s only approximately so. Centrifugal force of the Earth’s rotation around its polar axis makes it fatter across the Equator than between North and South Poles. Think of someone sitting on a basketball.

According to NASA’s Goddard Space Flight Center, the Earth’s equatorial diameter is 7926 miles; its pole-to-pole diameter, 7900 miles. This 26 miles is a mere 0.3 percent difference in diameter, but it has ramifications in identifying Earth’s extremes.

Mount Everest? Mount Chimborazo? Mount Everest’s 8848 m (29,029 ft.) is recognized as the highest point on Earth above global average sea level. However, as noted by the National Ocean Service, because of Earth’s centrifugal bulge, Ecuador’s Mount Chimborazo is “over 6800 ft. farther from Earth’s center than Everest’s peak.”

Image from the National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce.

Prominence. To topographers, a mountain’s prominence describes its local height, the vertical distance between its summit and the lowest contour line encircling it and no higher summit.

This is why, for example, I believe the Alps have more striking scenery than the Rockies.

Shall We Measure from Sea Level? Or? Other more regional aspects relate to prominence as well. For example, Mount Everest’s 29,029-ft. peak is in the already lofty Himalayas.

By contrast, Mauna Kea’s prominent 13,803 ft. is the tip of a largely submerged volcano. According to Wikipedia, “… when measured from its underwater base, Mauna Kea is the tallest mountain in the world, measuring 10,200 m (33,500 ft.) in height.”

Mauna Kea on the island of Hawaii. Image by Vadim Kurland from Wikipedia. The island of Hawaii from space. Image from NASA.

A Uniform Earth? Let’s imagine Earth free of its oceans, accept Mauna Kea’s total 33,500-ft prominence, and recall Challenger Deep’s 35,810-ft. trench of Kathy Sullivan’s adventure. Translated into miles, these two extremes are 6.3 and 6.8 miles, respectively.

Roughly, then, the Earth has an average diameter of around 7913 miles, with extremes of about ±6.5 miles. That’s a ±0.0008 variation and would seem uniform indeed.

Better than a Billiard Ball? According to the World Pool-Billiard Association, “All balls must be composed of cast phenolic resin plastic and measure 2 1/4 (+.005 ) inches [5.715 cm (+.127 mm)] in diameter and weight 5 1/2 to 6 oz [156 to 170 gms].”

Note the tolerance in diameter is one-way, + not ±.

If Earth were shrunk to the size of a billiard ball, its equatorial squat of +26 miles would translate to +.007 in., a skosh beyond the association’s allowable +.005 in. In a sense, then, Earth isn’t spherical enough for the World Billiard-Pool Association.

But, if interpreted differently, were a regulation billiard ball be enlarged to Earth’s size, its diametrical tolerance could give Planet Billiard a potential elevation extreme of +17.6 miles. Imagine a 92,928-ft. Mount Eight Ball.

Let’s avoid the matter of smoothness versus sphericity, as explorable by Googling “Billiard Ball vs Earth.” My current opinion is “it depends.” ds

© Dennis Simanaitis,, 2020


  1. fred vainas
    June 14, 2020

    I think it’s funny that you used a “magic” eight ball. I don’t think they’re built to the exacting specs required of a billiard ball.

    • simanaitissays
      June 14, 2020

      Your eye is sharp. Fact is, I was less discerning in my Google Image search. (And I never even asked a question….)

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