Measuring Earth

Measuring Earth

So the ancient Greeks believed that Earth was a ball. But just how large was Earth's ball - and how were planets?

In about 240 BC, a Greek astronomer in Egypt, Eratosthenes, made am exciting discovery. He found that when the Sun was directly overhead in one city, it cast a shadow in another city, 500 miles (800 km) to the north.

Eratosthenes figured that this meant Earth's surface curved. He also figured out that Earth was a ball about 25,000 mile (40,000 km) around. Today, we know he was right.

Hipparchus later studied Earth's shadow when it eclipsed the Moon. From the size of the Moon, he decided it must be about 240,000 miles (384,000 km) from Earth. He was right about that, too!


Binesh Das