This week’s question was asked by a friend.

QUESTION: Who first measured the size of the Earth?

ANSWER: Phillip V, king of Macedonia, commissioned Eratosthenes to get the job done in the year 240 BC. Today the countries of Croatia, Bosnia, Herzegovina, Montenegro, and Serbia sit where Macedonia was. It was already known that the Earth was a sphere, but no one knew how big a sphere.

Eratosthenes lived in the city of Alexandria, where the Nile River flows into the Mediterranean Sea. Alexandria had the most famous library in the known world. He had read that at noon on the summer solstice (June 21) in the city of Syene, Egypt, a vertical rod did not cast a shadow, but at his house in Alexandria, some 5,000 stadia (500 miles) north, on the very same day and time, a vertical rod cast a shadow of a bit more than seven degrees.

There’s another account that Eratosthenes read that on June 21, no shadow was cast in a well at Syene at high noon. Same idea − well or rod − it doesn’t make any difference.

Eratosthenes set up a simple ratio of seven degrees divided by 360 degrees equals 500 miles divided by the unknown circumference. He came mighty close to the true circumference of almost 25,000 miles.

Eratosthenes was a mathematics and science genius. He devised a system of latitude and longitude and a calendar that included leap years. He compiled a star catalog that showed 675 stars. Eratosthenes invented a mechanical device used by early astronomers to demonstrate and predict the apparent motions of the stars in the sky.

Some researchers claim that Eratosthenes measured the distance from the Earth to the Moon and the distance from the Earth to the Sun. Any proof of those accomplishments has been lost.

Eratosthenes yearned to understand the complexities of the entire world. In his three-volume work Geography, Eratosthenes described and mapped his entire known world, dividing the Earth into five climate zones: two freezing zones around the poles, two temperate zones, and a zone encompassing the equator and the tropics. We continue to use the system today. Eratosthenes is considered the father of geography and has a crater on the Moon named after him.

In old age, Eratosthenes became blind and died of self-induced starvation. He lived to age 82, quite remarkable for that time period.

Eratosthenes was a friend of Archimedes, who also lived and worked in Alexandria. Archimedes was the greatest mathematician and inventor of the age.

The king who hired Eratosthenes, Phillip V, had plenty of troubles of his own, especially with the Roman Empire. His younger son Demetrius kissed up to the Romans. The Romans, in turn, encouraged Demetrius to succeed his father, Phillip, ahead of the probable succession of the older son, Perseus. There was a quarrel between the two sons and it forced Phillip to reluctantly execute his younger son, Demetrius. That decision took a toll on Phillip’s health, as one might expect, and he died a year later, at age 59. His elder son Perseus did become the next king. “Uneasy lies the head that wears a crown,” Shakespeare would write centuries later in his play Henry IV.

Send questions and comments to: lscheckel@charter.net.

Larry Scheckel is a retired Tomah High School physics teacher.

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