According to what phenomenon did the ancient Greeks come to the conclusion that the earth was round?

The ancient Greek philosopher Pythagoras first proposed that the earth is spherical. One day, Pythagoras came to the seaside and looked at the sailboats coming from the horizon. He suddenly found an interesting phenomenon. At first, the mast tip always appears, then the sail appears, and finally the whole hull appears (Figure 1). After thinking, he concluded that the surface of the earth is round.

170 years later, the Greek philosopher Aristotle was the first to provide evidence for this statement. He found that when a person travels north, the heights of various stars in the sky are changing relative to the horizon (Figure 2). He also found that the edge of the moon was a circular shadow when the eclipse occurred. At that time, people already knew that the solar eclipse was formed because the earth blocked the sunlight from reaching the moon. From this, he thinks that the earth.

It was not until the beginning of the 6th century (16) that Magellan, a great navigator, sailed around the earth once. It turns out that the earth is spherical. In September, 2009, Portuguese explorer Magellan and his sailors set out from the Spanish port of San Rugar, sailed westward, crossed the Atlantic Ocean and reached the east coast of America, in order to find out the shape of the earth. They bypassed strait of magellan in South America and continued to sail in the endless Pacific Ocean. Overcoming all kinds of unimaginable difficulties, they finally arrived in the Philippine islands at 152 1 .36866.966966666666 Soon, Magellan died there. His crew continued to sail west, across the Indian Ocean and around the southern tip of Africa. The only Victoria among the five ships returned to Spain on September 6th, 1522. Their brother once completed the great cause of circling the earth once, and proved that the earth is spherical with his own experience. People named the "earth" according to Magellan's conclusion.