Eratosthenes, an astronomer in ancient Greece, measured the radius of Earth by making observations of:
A)the Sun's direction at midday at two positions on Earth, on the same day of the year.
B)the tidal ebb and flow of ocean waters.
C)the deviation of magnetic north, as seen from a compass, from true north.
D)relative times of arrival of the Sun due south of an observer at two positions on Earth.

Question

Quizplus · Accepted Answer

Eratosthenes measured the Earth's radius by observing the angle of the Sun's rays at midday in two different locations (Alexandria and Syene) on the same day of the year. He used the difference in the angles to calculate the circumference and thus the radius of the Earth.

Eratosthenes, an Astronomer in Ancient Greece, Measured the Radius of Earth