Eratosthenes knew that at noon on the longest day of the year—June 19—the sun would appear at its zenith in Syene (today, Aswan) Egypt. It would not cast a shadow. Measuring the angle of a shadow cast by the sun at noon in Alexandria, Eratosthenes found it to be 1/50th of a circle. Eratosthenes then calculated the distance between Syene and Alexandria, and correlated that distance to the circumference of his hypothetical circle.
Eratosthenes estimated the Earth to be about 46,620 kilometers (28,968 miles) in circumference, although historians and mathematicians disagree about how to interpret his conclusions. Using modern technology, we know the Earth is about 40,075 kilometers (24,902 miles) around the Equator—a difference of about 16 percent. Not bad.
Term Part of Speech Definition Encyclopedic Entry accuracy Noun
condition of being exact or correct.
slanting space between two lines that ultimately meet in a point.
part of the outline of a circle.
distance around the outside of a circle.
height above or below sea level.
Encyclopedic Entry: elevation Equator Noun
imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude.
Encyclopedic Entry: equator measurement Noun
process of determining length, width, mass (weight), volume, distance or some other quality or size.
the science of using tools and complex machines to make human life easier or more profitable.
point on the celestial sphere directly above a given position.