Eratosthenes measured the radius of Earth by:
A)timing the disappearance of the Sun at sunset for two different positions on Earth on the same day of the year.
B)estimating the size of the shadow of Earth on the Moon during a lunar eclipse.
C)measuring the angular position of the pole star from several positions on Earth.
D)noting the different angles of the Sun at midday on the same day of the year at different positions on Earth.

Question

Quizplus · Accepted Answer

Eratosthenes noticed that on a certain day of the year, the Sun was directly overhead in the Egyptian city of Syene, but was at an angle in Alexandria. By measuring the angle of the Sun's rays in Alexandria, he was able to calculate the angle between Syene and Alexandria. Using this angle and the distance between the two cities, he was able to calculate the circumference of the Earth, and from that, its radius.

Eratosthenes Measured the Radius of Earth By