June 19, 240 B.C.: The Earth Is Round, and It's This Big. Eratosthenes actually calculated the circumference of the Earth. Greek astronomer, geographer, mathematician and librarian. Eratosthenes calculates the Earth's circumference. His data was rough, but he wasn't far off.
Eratosthenes was an all-around guy, a Renaissance man centuries before the Renaissance. Some contemporaries called him Pentathalos, a champion of multiple skills. The breadth of his knowledge made him a natural for the post of librarian of the library of Alexandria, Egypt, the greatest repository of classical knowledge. He figured the circumference to be 252,000 stades. So how big is 252,000 stades? Depending on which classical source you trust, it's somewhere between 24,663 and 27,967 miles. The accepted figure for equatorial circumference today is 24,902 miles. Pretty darn good for a guy without modern measurement tools.
Eratosthenes went further and computed the tilt of the Earth's axis to within a degree. He also deduced the length of the year as 365¼ days. He suggested that calendars should have a leap day every fourth year, an idea taken up two centuries later by Julius Caesar.
Grade-school tales aside, it was thus known long before Columbus that the Earth was round and even how big it is, approximately. But it was just not widely known among the masses in 15th-century Europe. One reason is that Eratosthenes' very own library of Alexandria had been destroyed, and there was no complete backup of its data. Who knows how much information about the past was lost when the library burned.
Eratosthenes was an all-around guy, a Renaissance man centuries before the Renaissance. Some contemporaries called him Pentathalos, a champion of multiple skills. The breadth of his knowledge made him a natural for the post of librarian of the library of Alexandria, Egypt, the greatest repository of classical knowledge. He figured the circumference to be 252,000 stades. So how big is 252,000 stades? Depending on which classical source you trust, it's somewhere between 24,663 and 27,967 miles. The accepted figure for equatorial circumference today is 24,902 miles. Pretty darn good for a guy without modern measurement tools.
Eratosthenes went further and computed the tilt of the Earth's axis to within a degree. He also deduced the length of the year as 365¼ days. He suggested that calendars should have a leap day every fourth year, an idea taken up two centuries later by Julius Caesar.
Grade-school tales aside, it was thus known long before Columbus that the Earth was round and even how big it is, approximately. But it was just not widely known among the masses in 15th-century Europe. One reason is that Eratosthenes' very own library of Alexandria had been destroyed, and there was no complete backup of its data. Who knows how much information about the past was lost when the library burned.
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