Shape of the Earth
From the time we enter kindergarten we are told that the Earth is round, yet there is very little in our day-to-day experiences to tell us that this is true. Even from an airplane flying at normal commercial aircraft altitudes (35 to 45 thousand feet) the Earth appears as flat as a pancake with rivers, valleys, and mountains breaking its flatness. Today, we have little reason to doubt that the Earth is a sphere. We have seen photographs that have been taken from artificial satellites in orbit around the Earth and the Moon.
People knew the Earth was spherical over 2,500 years ago. This was concluded from observations of the Sun and Moon. The Greek philosopher Pythagoras concluded in 500 B.C., that the Earth must be round because the Sun and Moon are round. Two hundred years later the philosopher Aristotle taught his students that the Earth had to be round because the shadow of the Earth falling on the Moon during a lunar eclipse is always circular. Aristotle reasoned that the only solid body that consistently gives a circular shadow is a sphere. Therefore, the Earth must have a spherical shape. (Activity I: Proof That the Earth is Spherical)
These conclusions were supported by observant travelers over both land and sea. Sojourners noted that certain bright stars in the northern sky appeared higher in the sky the farther north they traveled while stars in the southern sky disappeared below the horizon. The opposite occurred as they traveled southward. This can only happen if one is traveling over a circular surface.
Years of collecting evidence to verify the Earth's spherical nature
finally allowed scientists to show that the Earth is not a true sphere, but
rather an oblate spheroid. An oblate spheroid is a sphere that bulges at
the equator and is flattened at the poles. This was proven by an expedition
to measure accurately one degree of latitude at various distances from the
equator to the North Pole. These scientists showed that the land distance
of one degree latitude at the equator is equal to 110.813 kilometers
(68.704 miles). The same one degree of latitude near the North Pole is
equal to 111.947 kilometers (69.407 miles). If the Earth were a perfect
sphere these distances would be the same at all places on Earth.
