Evidence of earth's sphericity upsc

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Spherical Earth

Approximation of the figure of Earth as a sphere

"Round world" redirects here. For other uses, see The World is Round.

Not to be confused with Earth ball.

Spherical Earth or Earth's curvature refers to the approximation of the figure of the Earth to a sphere. The concept of a spherical Earth gradually displaced earlier beliefs in a flat Earth during classical antiquity and the Middle Ages. The figure of the Earth is more accurately described as an ellipsoid, which was realized in the early modern period.

Cause

Main article: Equatorial bulge

See also: Hydrostatic equilibrium § Planetary geology

Earth is massive enough that the pull of gravity maintains its roughly spherical shape. Most of its deviation from spherical stems from the centrifugal force caused by rotation around its north-south axis. This force deforms the sphere into an oblate ellipsoid.^[1]

Formation

Further information: History of Earth

The Solar System formed from a dust cloud that was at least partially the remnant of one or more supernovas that pro

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Sea and Space / Navigation / Astronomical

The Shape of the Earth

Since ancient times, mankind has pondered about the geometrical shape of our planet Earth.

Aristotle (384-322 BC) was among the first to recognize the fact of our planet being a round sphere. He observed lunar eclipses and noticed that only a round sphere could imply a circular shadow.

This astronomical observation was confirmed by general observations made at sea. When a ship sails away from the coast, it seems to disappear gradually behind the horizon.

The next scientific step, directly measuring the size of our planet, was performed by Erathostenes (276-194 B.C.).

In 1996 - 97, several EAAE - Astronomy On-Line students have repeated these measurements: click to see a general description. Their results did fit within 10 percent of the true values.

Based on reports by sailors, Erathostenes actually prepared reasonably accurate maps of the lands and seas known to him.

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The World Map by Erathostenes, approx. 250 BC

Later, efforts were made by Ptolemeus to improve the maps b

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ANCIENT

ARISTOTLE (384 B.C. - 322 B.C.)
Aristotle believed that the universe was spherical and finite. He also believed that the earth was a sphere, much smaller than the stars. To support his theory, he used observations from lunar eclipses stating that lunar eclipses would not show segments with a curved outline if the earth were not spherical. Additionally, he stated that when a person travels north or south, they do not see the same night stars, nor do they appear in the same positions in the sky.

Around this time there was a common belief that four basic elements existed: earth, air, fire, and water. In addition to these elements, Aristotle believed that there was a fifth element called aether, which he thought to be the basic make up of the celestial bodies. His view of the universe was hierarchical, and he made a distinct difference between the earth and the heavens.

According to Aristotle's theories of motion, he believed that there were three kinds: rectilinear, circular and mixed. He theorized that the four elements tended to move in straight lines. The earth