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NASA's images of the Earth may seem round when viewed from space, but our planet is actually very much oblong.
NASA's photos seem to show that the Earth is round from space, appearances, however, can be deceiving because planet Earth is in fact, oblong.
So it turns out that the Earth is not flat or round. Well before Columbus sailed the ocean blue, Aristotle and other ancient Greek scholars proposed that the planet was oblong. This was based on a number of observations, such as the fact that departing ships not only appeared smaller as they sailed away but also seemed to sink into the horizon, as one might expect if sailing across an oblong object says geographer Bill Carstensen of Virginia Tech in Blacksburg.
Isaac Newton first proposed that Earth was not perfectly round. Instead, he suggested it was an oblong shape—a sphere that is squashed at its poles and swollen at the equator. He was correct and, because of this bulge, the distance from Earth's center to sea level is roughly 21 kilometers (13 miles) greater at the equator than at the poles.
Instead of Earth being like a spinning top made of steel, explains geologist Vic Baker at the University of Arizona in Tucson it has "a bit of plasticity that allows the shape to deform at the equator. The effect would be similar to spinning a bit of Silly Putty, the Earth's plasticity is very much like that of the silicone plastic clay so familiar to children."
Our globe, however, is not even a perfect oblate spheroid, because mass is distributed unevenly within the planet. The greater a concentration of mass is, the stronger its gravitational pull, "creating bumps around the globe," says geologist Joe Meert at the University of Florida in Gainesville.
Earth's shape also changes over time due to a menagerie of other dynamic factors. Mass shifts around inside the planet, altering those gravitational anomalies. Mountains and valleys emerge and disappear due to plate tectonics. Occasionally meteors crater the surface. And the gravitational pull of the moon and sun not only cause ocean and atmospheric tides but earth tides as well.
In addition, the changing weight of the oceans and atmosphere can cause deformations of the crust "on the order of a centimeter or so," notes geophysicist Richard Gross at the Jet Propulsion Laboratory in Pasadena, Calif. "There's also postglacial rebound, with the crust and mantle that were depressed by the huge ice sheets that sat on the surface during the last ice age now rebounding upward on the order of a centimeter a year."
Moreover, to even out Earth's imbalanced distribution of mass and stabilize its spin, "the entire surface of the Earth will rotate and try to redistribute mass along the equator, a process called true polar wander," Meert says.
To keep track of Earth's shape, scientists now position thousands of Global Positioning System receivers on the ground that can detect changes in their elevation of a few millimeters, Gross says. Another method, dubbed satellite laser ranging, fires visible-wavelength lasers from a few dozen ground stations at satellites. Any changes detected in their orbits correspond to gravitational anomalies and thus mass distributions inside the planet. Still another technique, very long baseline interferometry, has radio telescopes on the ground listen to extragalactic radio waves to detect changes in the positions of the ground stations. It may not take much technology to understand that the Earth is oblong, but it takes quite a bit of effort and equipment to determine its true shape.
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