How did Eratosthenes know the exact time?

Eratosthenes actually measured the length of the shadow of a tall building in Alexandria when the Sun reached its highest point in the sky on the Summer Solstice. This corresponds to noon in both Alexandria and Syene, where the Sun cast no shadow at the bottom of a deep well (hence the Sun was directly overhead).

How did Eratosthenes measure the shadows at the same time?

On that day, the sun at noon was directly overhead at Aswan. On the same day, Eratosthenes measured the shadow of the a stick at noon in Alexandria. In the figure, a vertical stick at point A would cast no shadow, a stick at B would cast a “moderate” shadow, and a stick at C would cast a very long shadow.

How did Eratosthenes know it was 7 Degrees?

Eratosthenes had heard that in Syene, a city south of Alexandria, no vertical shadows were cast at noon on the summer solstice. So, on June 21 he planted a stick directly in the ground and waited to see if a shadow would be cast at noon. It turns out there was one. And it measured about 7 degrees.

Which time did Eratosthenes observe the shadows cast by a vertical stick?

noon
Eratosthenes’ experiment (205 BC) gave the first estimation of the Earth’s radius simply by observing the shadow of a vertical stick at noon local solar time.

What did Eratosthenes discover?

What is Eratosthenes famous for? Eratosthenes measured Earth’s circumference mathematically using two surface points to make the calculation. He noted that the Sun’s rays fell vertically at noon in Syene (now Aswān), Egypt, at the summer solstice.

How did Eratosthenes measure the distance from one well to another for his calculation?

He measured the length of the shadow of a tall tower in Alexandria, and used simple geometry to calculate the angle between the shadow and the vertical tower. Eratosthenes had the distance between the two cities measured. His records show that the distance was found to be 5,000 stadia.

What is the circumference of the earth according to Eratosthenes calculation?

If we accept the account of Strabo that Eratosthenes measured the circumference of the earth as 252,000 stadia, the circumference would be 24,662 miles, and the polar diameter 7,850 miles-only 50 miles short of the true polar diameter. This is considered to be one of the first great triumphs of scientific calculation.

What do you know about Eratosthenes?

Eratosthenes, in full Eratosthenes of Cyrene, (born c. 276 bce, Cyrene, Libya—died c. 194 bce, Alexandria, Egypt), Greek scientific writer, astronomer, and poet, who made the first measurement of the size of Earth for which any details are known.