To Accurately Calculate Earth’s Circumference

To Accurately Calculate Earth’s Circumference

How was a man living over 2,000 years ago able to accurately calculate Earth’s circumference? How could he even know that Earth is spherical? How can some people today believe that our planet is flat when everyone has seen pictures of Earth taken by satellites in space?

Those may be too many questions at once. Let’s try looking at them one at a time. The first man to accurately calculate Earth’s circumference in about 240 B.C. was a Greek polymath named Eratosthenes. He was a brilliant mathematician, geographer, astronomer, music theorist, and poet, and his calculations were amazingly accurate.

A myth originated from a fiction work by nineteenth-century American author Washington Irving and other authors. Irving wrote a less-than-accurate “biography” of Christopher Columbus. In it, the Spanish authorities questioned Columbus’ plan to sail west to Asia by going east because they thought the ships would drop off the edge of a flat Earth. The truth is that European scholars at that time knew that our planet is a sphere. In fact, Columbus did too, but he believed that it was 25% smaller than it actually is. He should have paid more attention to Eratosthenes.

Ancient Greek scholars, as early as the fifth century B.C., recognized the spherical nature of the planet based on observations. (We have talked about that before.) So Eratosthenes set out to accurately calculate Earth’s circumference. Let’s look at a simplified description of how he did it.

Eratosthenes was the librarian of the famous library of Alexandria in Egypt. Syrene was a city 5,000 stadia south in what is now Aswan, Egypt. (5000 stadia was approximately 800 km or 497 miles.) At noon on the summer solstice, Eratosthenes placed a rod vertically into the ground in Alexandria. At the same time, his assistant had placed a rod of the same length at Syrene. Since Syrene is very close to the Tropic of Cancer, where the Sun is directly overhead at noon on the solstice, the rod did not leave a shadow. In Alexandria, the rod produced a shadow of 7 degrees, which is 1/50 of the circumference of a circle. That means Earth’s circumference would be 50 times the distance from Alexandria to Syrene. Multiplying 50 times 5,000 stadia results in 250,000 stadia for Earth’s circumference. Depending on exactly how long a stadion was, that measurement is accurate to within -2.4% to +0.8%.

That answers the first two questions, but what about people today who believe the Earth is flat when there is plenty of evidence otherwise? That is an example of people believing what they want to believe and refusing to accept the evidence. There is a connection here to the so-called war between science and faith, and it relates to what we read in Romans 1:20. More on that tomorrow.

— Roland Earnst © 2023

Vernal Equinox Arrives Today

Vernal Equinox Arrives Today

The orbit of the Earth around the Sun produces variations in the seasons with four orbital positions having particular significance. Today, March 19, 2020, the Sun will pass directly overhead at the equator. The exact time will be 11:49 p.m. EDT (0349 GMT March 20, 2020). We can rejoice that the vernal equinox arrives today!

This is the earliest equinox in the United States in 124 years! As you can see in the diagram, the usual date for the vernal equinox is March 20 or 21, depending on where you live on the Earth. The reason it arrives on the 19th this year in North America is somewhat complicated, but it has to do with leap years and daylight saving time. We won’t get into that, but I thought we should explain why the diagram differs from this year’s dates.

There is wonderful history of how the Greek scholar Eratosthenes of Alexandria used the equinox to measure the circumference of the Earth. He knew that on the equinox, a pole stuck vertically in the ground left little or no shadow at noon, depending on location. He compared the length of the shadow of a pole in Syene, a town in southern Egypt, with one in Alexandria in northern Egypt. Using the difference in the shadow lengths, he calculated the circumference of the Earth. His calculation was very close to the known circumference today, and it proved the Earth was round. He did that in 245 BC, long before Columbus sailed.

The four polar positions roughly predict the seasons that have been used by every culture to control planting, harvesting, and preparing the soil. In Genesis 1:14, God said, “Let there be lights in the expanse of space to divide the day from the night, and let them be for signs, and for seasons, and for days, and years.” God not only instituted day and night, but He also positioned the Sun and Moon so they could be used to mark the seasons we would need to live on this planet.

As the vernal equinox arrives today, we wish you a happy equinox!! Enjoy the season and the official end of winter in the Northern Hemisphere. We will have more on the spring equinox tomorrow.

— John N. Clayton and Roland Earnst © 2020

Operating on Faith

 Operating on Faith - Eratosthanes

Philosopher Rene Descartes (1596-1650) told the story of a king who refused to eat until he knew with certainty that his food had not been poisoned. The more he thought about how little he knew with certainty about his chef and his attendants, the more concerned he became. He finally starved to death. This story makes the point that everyone is operating on faith.

Atheists ridicule Christians for operating on faith not realizing that they depend on faith, and so does science. A classic example was a Greek scholar named Eratosthenes of Cyrene born in 276 BC. Eratosthenes noticed that on a specific day of the year, the Sun was positioned so that it illuminated the bottom of a well where he lived. From that fact, he had faith that the Earth was spherical.

On the day that the Sun shone to the bottom of the well in Syene (modern Aswan, Egypt), Eratosthenes placed a vertical rod in the ground at Alexandria and measured the angle of its shadow. Using the difference in angle of the Sun’s rays and the distance between the two locations, he calculated the circumference and diameter of the Earth with high accuracy. He even established the concept of latitude and longitude from his measurements. Scholars of Eratosthenes’ day ridiculed his idea because everyday experience suggested the Earth was flat and endless. They indicated that he was mistaken or his measurements were wrong. Their criticism did not sway the strong faith of Eratosthenes in what he believed.

A modern-day Eratosthenes would be Albert Einstein. His radical ideas were still not accepted by many in the scientific community some 40 years after he originally proposed them. The critics were silenced only when Einstein’s ideas could finally be tested and proven correct.

For many scientific discoveries in the past, that pattern has been repeated. A scientist operating on faith expressed a hypothesis based on his or her observations. The hypothesis could not be tested when the concept was proposed, but from that faith, something important was eventually discovered.

The definition of faith in Hebrews 11:1 fits this scientific concept of how discoveries are made: “Faith forms the solid ground of things hoped for, perceiving as real what is not revealed to the senses.” (Amplified Bible).

–John N. Clayton © 2019