I found this on Answers In Genesis.
Reasons We Know That the Earth Is Spherical
Earth’s Shadow
So how did people in the ancient world know that the earth is spherical? The earliest recorded discussion of a spherical earth is from Pythagoras in the sixth century BC. Pythagoras correctly understood that the cause of lunar eclipses is the shadow of the earth falling on the moon. This can happen only when the moon is opposite the sun in our sky, which coincides with full moon. The earth’s shadow is larger than the moon, so we cannot see the entire shadow at once. However, during a lunar eclipse we see the earth’s shadow creep across the moon. Because the edge of the earth’s shadow always is a portion of a circle, the earth’s shadow must be a circle. If the earth were flat and round, similar to a disk, it could cast a circular shadow, but only for lunar eclipses that occur at midnight. For a lunar eclipse at sunrise or sunset, the earth’s shadow would be an ellipse, a line, or a rectangle, depending upon how thick the disk was compared to its diameter. However, the earth’s shadow during a lunar eclipse is always a circle, regardless of the time of night when the eclipse occurs. The only shape that consistently has a circular shadow, regardless of its orientation, is a sphere.
The only shape that consistently has a circular shadow, regardless of its orientation, is a sphere.
Visibility of the Stars
Another argument involves the stars that are visible in the northern and southern parts of the sky. The North Star lies within a degree of the north celestial pole, the direction in space that the earth’s rotation points at. As the earth rotates each day, the stars, the sun, and the moon appear to spin around the north celestial pole, so the north celestial pole remains fixed in the sky. In the ancient world, many people thought that the celestial sphere rotated each day around a non-spinning earth. For our purposes here, it doesn’t matter which is the case. The north celestial pole makes an angle with the northern horizon. We call this angle the altitude of the north celestial pole. Since the North Star is so close to the north celestial pole, we can approximate the altitude of the north celestial pole with the North Star’s altitude.
Vela and Surrounding Constellations
The altitude of the North Star is noticeably higher in the sky at northern locations than it is at southern locations. For example, the North Star is much higher in the sky in the northern United States and Canada than it is in Florida, as anyone who pays attention on a trip, such as a vacation, can attest. This can happen only if north-south motion is along an arc. This is further underscored by other considerations. There is a region around the North Star in which the stars do not rise or set but instead are continually up and appear to go in circles around the north celestial pole. We call these circumpolar stars, meaning “around the pole.” The region of circumpolar stars is larger at northern locations than in southern locations. Likewise, there is a circumpolar region below the southern horizon whose stars are always below the horizon. The northern circumpolar region, where stars are always visible, is very large, and the southern circumpolar region, whose stars are never visible, is also large. Closer to the earth’s equator, the two circumpolar regions are smaller. For example, for many years I lived in South Carolina, about four degrees farther south latitude from where I now live in Northern Kentucky. I can see that the North Star is slightly higher in Northern Kentucky than it was in South Carolina. Furthermore, during winter in South Carolina, the bright star Canopus barely rose above the southern horizon each night; but in Kentucky I can never see Canopus. This is because in Northern Kentucky, Canopus is in the southern circumpolar region where stars are never visible, while in South Carolina it is not. This too shows that the earth is curved in the north-south direction.
Curvature of the Earth
Not only is the earth curved in the north-south direction, it also is curved in the east-west direction. There is a time difference of three hours between the east and west coasts of the United States. That is, the sun rises and sets approximately three hours earlier on the east coast than it does on the west coast. This is easily verified by anyone who has flown between the east and west coasts of the United States. Not only will your watch show that there is a time difference of three hours, but your body will notice the difference in time as well. If one drives from one coast to the other, the trip will take several days, so our bodies will not notice the time difference as much. However, our watches reveal that the time has changed. Such rapid transportation was not possible in ancient times, but the ancients could see this time difference a different way. A lunar eclipse obviously must happen simultaneously for everyone on earth, but it will be different times at different locations. For instance, a lunar eclipse may start shortly after sunset in the eastern Mediterranean, such as in Greece. However, in the western Mediterranean, such as in Spain, the moon would already be in eclipse when the moon rose that night. This means that the lunar eclipse began before sunset/moonrise in Spain, but after sunset/moonrise in Greece. Communication was such in the ancient world that people were aware of this effect. This shows that the earth is curved in the east-west direction. If the earth is curved in both the north-south and east-west direction, the most likely shape of the earth is a sphere.
Ancient Sources
Ancient sources, such as Aristotle, also mentioned that the hulls of ships disappeared before their masts did as ships sailed away. This would happen only if the earth is spherical. Without optical aid, this is difficult to see. However, one easily can see a related effect. If one is perched atop the mast of the ship, one can spot land or other ships before people on the deck can. This is why spotters often were placed in a crow’s nest high above a ship’s deck. If the earth were flat, there would be no advantage to being above the deck. A similar thing can be observed on land. The Door Peninsula in Wisconsin forms the eastern shore of Green Bay. The distance across Green Bay from the northern portion of the Door Peninsula to Northern Michigan is more than twenty miles. Looking across Green Bay from the beach on the west side of the Door Peninsula, one cannot see Northern Michigan. However, if one ascends the bluffs above the beach, one can see the shoreline of Northern Michigan. This is possible only if the earth is spherical.
Not only did ancient people know that the earth was spherical, one of them accurately measured the size of the earth around 200 BC. Eratosthenes worked at the Great Library in Alexandria, Egypt. Eratosthenes is the father of geography because he coined the term and commissioned the creation of many maps. One particular year on the summer solstice, Eratosthenes was in southern Egypt near modern-day Aswan. Being on the northern limit of the tropics, the sun was directly overhead at noon on the summer solstice. Eratosthenes realized this, because he could look down into a deep well and see the bottom.
Normally, the bottom of a well is not visible because the sun’s light does not shine directly on the bottom, but it did at noon on the summer solstice because the sun was directly overhead. The sun never was directly overhead in Alexandria, because it is not in the tropics. Back in Alexandria the following year, Eratosthenes measured the altitude of the sun at noon on the summer solstice. He did this by constructing a vertical pole of known height and measuring the pole’s shadow at noon. Trigonometry allowed Eratosthenes to compute the sun’s altitude. The difference between ninety degrees and the altitude was how far the sun was from being vertical. Eratosthenes found that the angle was about one-fiftieth of a circle. This meant that Alexandria and Aswan were separated by one-fiftieth of the earth’s circumference. Eratosthenes knew the distance between those two locations, so multiplying that distance by fifty gave him the earth’s circumference.
Why do so many people today assume that everyone thought that the earth was flat until the time of Columbus? The argument at the time of Columbus was not over the earth’s shape, but over the earth’s size. Muslims had closed to Europeans the overland trade routes to the Far East. Everyone realized that travel to Asia by sailing west from Europe was possible, but why would you want to? There was a vast ocean (they didn’t know about the two American continents in between) separating Europe and Asia. It was much shorter to sail eastward from Europe, perhaps around Africa, to reach Asia. In the small ships used at the time, it was not advisable to sail more than a few days out of sight of land. Columbus was proposing a voyage of a few months over open, uncharted waters. That was very dangerous. To make his proposed voyage more palatable, Columbus overestimated the eastward distance from Europe, and at the same time he decreased Eratosthenes’ measurement of the earth’s circumference. The difference in these two was Columbus’ expected distance to Asia by sailing westward from Europe. In Columbus’ estimation, it was shorter to reach Asia by sailing westward than eastward. A glance at a modern globe or map of the world reveals that this is false. In other words, Columbus was wrong, and his critics were right!
Accusation of Christianity
In the late nineteenth century, two atheistic skeptics, Andrew Dickson White and John Draper, created the conflict thesis that Christianity held back the progress of science. One of their major arguments was that throughout the Middle Ages the church had taught that the earth was flat. In creating this myth, Draper and White suggested that the church could redeem itself for this supposed error on the earth’s shape by getting in on the ground floor of Darwinism. This ploy was very successful in that much of the church capitulated on evolution. It also falsely altered history. It is this false version of history that most people have learned.
It's a figure of speech----meaning as far as you can see---which in a flat dessert is a lot further than in a jungle.
