Since prehistoric times, before the advent of modern technology everyone believed that the shape of the Earth was flat. Starting from the ancient Greek era, the bronze age, the iron age, until the 17th century. The flat earth became the culture of the American Aboriginal tribe, where according to him the Earth was a flat disk with a cupola dome that was inverted bowl, filled with stars, the sun and the moon that was sticking and moving were controlled by God.
The flat earth is supported by the holy books and religious leaders of the time, the upper part of the atmosphere called the firmament, a dense, broad dome. According to the story of creation, God made a firmament to separate the water above the Earth and water on the surface of the Earth. Because above the firmament is the world for the saints, gods, and heaven where God is, no one can penetrate it even with any sophisticated technology.
Meanwhile, the round earth theory has actually been alluded to by Pitagoras since 6 centuries BC, then empirically proven by Aristotle about 330 years BC. But more believed the earth was flat at the time. Gradually the belief in flat earth began to be abandoned and round earth was spread as the basis of learning in science subjects at school.
The round earth is very reasonable because it is interconnected with the theory of gravity and other physical theories. Round earth can be proven by exploring going in one direction and then it will automatically return to the place of origin. The people who first explored the entire planet Earth were Ferdinand Magellan and Juan Sebastián Elcano, their journey began from Seville, Spain, in 1519 and then headed west to continue across the Atlantic, Pacific and Indian oceans to return to their original place in 1522.
Another example that we can practice is that the earth is round in shape by going to the beach and seeing ships in the distance through binoculars or binoculars, if the Earth is rounded, the surface of the Earth will cover part of the hull. So if the ship approaches us, what is seen is the top like the sail, the flag, then the chimney, or the muzzle first.
But is it true that the shape of the Earth is round?
Apparently not really, the actual shape of the Earth is "oval".
This explanation is based on scientific American,
Isaac Newton first proposed that the Earth is not perfectly round. Instead, he suggested the earth be shaped like a ball squashed at the poles and protruding at the equator. He was right and because of this bulge, the distance from the center of the earth to sea level was about 21 kilometers (13 miles) greater at the equator than at the poles.
The Earth is not like rotating steel, geologist Vic Baker explained at the University of Arizona in Tucson. "It has a little elasticity that allows its shape to change somewhat. The effect will be similar to clay or night spinning. Despite the fact the Earth's elasticity is much smaller than on the silicone plastic clay that kids often play with. "
Our globe, however, is not a perfectly round oblate ball, because mass is distributed unevenly on this planet. The greater the mass concentration, the stronger the gravitational pull, "creating lumps all over the world," said geologist Joe Meert at the University of Florida in Gainesville.
The shape of the Earth also changes with time due to other dynamic factors. Mass shifts within the planet, changing its gravitational anomaly. Mountains and valleys appear and disappear due to plate tectonics. Sometimes the surface of the meteor crater. The gravitational pull of the moon and the sun not only causes ocean and atmosphere tides but also the earth tides.
Changes in the weight of the ocean and atmosphere can cause deformation of the Earth's crust "on the order of centimeters or more," notes geophysicist Richard Gross at the Jet Propulsion Laboratory in Pasadena, California. "There is also a postglacial rebound, on the crust and mantle depressed by the large ice sheets that have been on the surface in the last ice age until now soaring upwards in the order of centimeters every year." "All of the earth's surface will rotate and try to redistribute the whole equator, a process called true polar wander," Meert said.
To track the shape of the Earth, scientists are now positioning thousands of Global Positioning System receivers in the field that can detect changes in elevations of several millimeters, Gross said. The method, dubbed as a laser satellite gauge, launches long laser waves that are visible from several ground stations detected on the satellite. Every change detected in its orbit is adjusted to the gravity anomaly and the distribution of mass inside the planet. There are still other techniques, namely very long basic interferometry, through radio telescopes to listen to extragalactic radio waves to detect changes in the position of underground stations. It might not take much technology to understand that the Earth is not perfectly round, but it takes a little effort and equipment to determine its original form.
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