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The Earth’s circumference was first accurately measured more than 2,200 years ago by a Greek astronomer named Eratosthenes. Eratosthenes method was very simple; he measured the length of a shadow from a vertical stick of a known height in two cities on the same day.
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A century after Eratosthenes, the Greek astronomer Posidonius of Rhodes (c. 135–51 BCE) calculated the Earth’s circumference. Posidonius used the star Canopus as frame of reference: when the star is visible at the horizon in Rhodes, it is 7.5 degrees above the horizon in Alexandria.
BACKGROUND. At around 200 BC, Eratosthenes (c. 276 BC - c. 197 BC) determined the circumference of Earth with remarkable accuracy. As related accomplishments, he also demon-strated that Earth is essentially spherical and measured the tilt of its axis (23.5°).
Eratosthenes' method for determining the circumference of the Earth, with sunbeams shown as two rays hitting the ground at two locations in Egypt – Syene (Aswan) and Alexandria. Earth's circumference is the distance around Earth. Measured around the equator, it is 40,075.017 km (24,901.461 mi).
31 maj 2018 · Eratosthenes obtained a value close to 7.2 degrees, or 1/50th the circumference of a circle. To finish his calculation he needed a sufficiently accurate estimate of the distance between the two cities.
This chapter examines the ancient and modern sources available for the study of Eratosthenes’ experiment to calculate the circumference of the Earth in the third century BC. This chapter also contains a biography of Eratosthenes which looks at his life, education, career, and the city in which he grew up (Cyene).
4 wrz 2021 · How did Greek librarian Eratosthenes accurately measure the circumference of Earth using a stick, a shadow, and a walk?
