LITMIR.BIZ

      Figure 2.5. Image of earth from balloon. (Courtesy Wikimedia Commons.)

      8. Compare shadows: If you are motivated, you can replicate Eratosthenes’s famous experiment (fig. 2.1) yourself. The simplest way to do it would be to take a long flight in a north-south direction. Before you take off, measure the length your shadow casts at a particular time of day at your starting point. Take the flight, and then at the same time on the following day, measure the shadow at your new location. It should be measurably longer or shorter if you have traveled far enough. If the earth were a flat disk and not a sphere, this would not happen, because the sunlight coming in at an angle on a flat disk would always cast the same length of shadow.

      9. Compare time zones: As anyone with jet lag can tell you, traveling east to west, or west to east, around the earth for any significant distance is discombobulating, because changing time zones upsets your biological clock. This is a direct demonstration of how different parts of the spinning earth are facing the sun at different angles, so they are all experiencing a different time of the day relative to the sun. The easiest way to confirm this in this world of instantaneous satellite communication (which in itself is a confirmation of the spherical earth) is to compare the time you are experiencing in your area with the time of someone in a different part of the world. For example, if it’s noon in New York and you email or text or call a friend in Beijing, it’s midnight there, and it’s 1:30 a.m. in Adelaide, Australia. Or if you look up the times for sunrise and sunset at different longitudes around the earth, you see that they occur at different times. This is simply impossible with a flat earth. Flat- earthers have tried to get around this problem by claiming that the sun’s light casts a big circular flat “spotlight” that is pointing in a circle around the different parts of the earth, but that explanation falls apart if you think about it. If you were in a large darkened theater, you could still see the spotlight casting its light on the stage even though you might be in total darkness where you sit.

      10. Compare seasons: If the earth were flat, the sun’s rays would hit all parts of the earth from straight above and would not come in at an angle, like they actually do. In addition, there would be no seasons, because on a flat earth, both the Northern and Southern Hemispheres would get the same amount of solar radiation all year round. We would all experience whatever seasons there were the same way. But thanks to the spherical shape of the earth and its tilted axis, we experience seasons at different times, so winter in the Northern Hemisphere is summer in the Southern Hemisphere, and vice versa.

      11. Feel the pull of gravity: If you accept the laws of gravity worked out by Isaac Newton, then the force of attraction of gravity should get stronger the closer you are to the center of mass. In a flat-earth disk (fig. 2.2), gravity should be strongest in the center of the disk at the North Pole and much weaker as you approach the Antarctic, on the edge of the disk. If you dropped an apple in Australia or southern Patagonia, it should fall somewhat sideways, pulled toward the North Pole, not straight down—but it doesn’t. Anyone with a decent gravimeter (a device that measures gravitational attraction) can measure the gravity anywhere on earth, and the attraction at sea level is nearly always the same (except for local effects like crustal rock beneath you, which is denser or less dense than average). The scientific data for these gravity measurements have been gathered for more than a century and are widely published, although flat-earthers reject all scientists as part of the global conspiracy that includes NASA. (Of course, many flat-earthers don’t believe in gravity, either, but fall back on Aristotle’s antiquated notions that objects fall because they are heavier or lighter.)

      12. Consider the solar system: Anyone with a decent telescope, good night visibility, and a chance to look at the moon or the other planets night after night can confirm what early astronomers (especially Galileo) could see: all the other bodies in the solar system are spherical. You can see the shape of the moon clearly, especially as the shape of the illuminated part of the moon changes with the cycle of the full and new moons every month. After several nights of closely observing Jupiter in a good telescope, you can confirm that it is round and spinning on its axis; even better, each night you can see its four largest moons moving around as they orbit around it. It’s a lot more difficult to do this with Mars or Saturn, but Galileo was able to see it when he first trained a telescope to the skies. So if all the other bodies in space are spherical, why would only the earth be flat?

      If that’s not convincing enough to fair-minded flat-earthers or to people sitting on the fence on the issue or having doubts about the shape of the earth, then they are hopelessly lost in the mind-set of a cultist, and no amount of evidence will convince them. Sometimes they accidentally reveal the disconnect between their worldview and reality, as when a tweet from the Flat Earth Society read, “The Flat Earth Society has members around the globe.” Then there is the humorous internet meme “The only thing flat-earthers have to fear is sphere itself.” So we will consider this case closed and will move on to the next weird idea about earth: geocentrism.

      Ptolemy Revisited

       Religion versus Science

      The scene is a dramatic one, depicted in many plays and novels. Galileo Galilei, now sixty-eight years old, gray haired, losing his sight, and bowed with age, stands before the Inquisition in early 1633 (fig. 3.1). He is on trial for heresy, since he has advocated the notion that the sun is the center of the solar system (heliocentrism), a view first published by Nicholas Copernicus in 1543. This contrasts with geocentrism, the plain, intuitive common-sense idea that the earth, not the sun, is the center of the universe, as Aristotle and people since earliest times long believed (fig. 3.2). In 1609, using one of the first telescopes ever built (invented almost simultaneously in Holland and in Venice) to study the night sky, Galileo concluded that the earth moved around the sun, and he published his celestial observations and ideas in a short book titled Sidereus Nuncius (“Heavenly Messenger”) in 1610.

      By 1616, the Inquisition was scrutinizing his works for signs of heresy. They warned Galileo that he could talk about heliocentrism in a theoretical way but not actually claim that the earth really did move around the sun. Trying to steer clear of antagonizing the Church, Galileo argued that heliocentrism could be made consistent with religious dogma. But Church leaders disagreed, citing such passages as Psalms 93:1 and 96:10 and many other verses. In 1 Chronicles 16:30, the Bible says, “The world is firmly established, it cannot be moved.” Psalm 105:5 reads, “The Lord has set the earth on its foundations; it can never be moved.” Another example is Ecclesiastes 1:5, which says, “And the sun rises and sets and returns to its place.” And in Joshua 10:12, the Hebrew leader Joshua calls on the Lord to make the sun stand still so that they can continue their battle. Thus, Galileo was fighting not only thousands of years of established belief in geocentrism but also the Scriptures, since Europe was still ruled by either the Catholic Church or the Protestants.

      Figure 3.1. Painting of Galileo defiantly facing the Inquisition. (Courtesy Wikimedia Commons.)

      The last straw for the Church fathers was the 1632 publication of Galileo’s provocative book Dialogue Concerning the Two Chief World Systems. Encouraged by the election of his supporter Cardinal Maffeo Barbarini as Pope Urban VIII and the support of some Italian nobles, Galileo framed the argument as a dialogue, a miniature play between three characters.

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