Lesson 28: This lesson is really complicated!!! Basically a guy named Eratosthenes around 3rd century BC was able to understand that the world is round, and then he used some crazy math to calculate the circumference of the earth. He was able to do this by measuring the angles of shadows in different cities. In one city at exactly noon on a certain day, the shadow was not there because the sun was directly overhead, and the next year, on the exact same day and time, he measured the shadow of a pole. He used this to calculate what degree of change of tilt there was from one pole to the other pole, and then also the distance between the two cities to figure out the circumference of the earth. I didn’t really understand how the math part worked out, so I’m excited to see it in class!
Lesson 29:Hipparchus and the Moon
Hipparchus was very interested in why the moon sometimes appears to be larger in the night sky. He built a device to help him measure the size of the moon. His device helped him to determine that the size of the moon does not change size, but it only appears to, it is an optical illusion. It seems to be larger when it is at the horizon, because your brain naturally compares its size to the objects around it, like silhouettes of trees, houses and hills. Conversely, when it is up high in the sky, it is not near anything, and so it looks smaller. Many centuries later, scientists discovered that the moon doesn’t travel around the earth in a circle, but rather in an oval. This is barely perceptible because it is so slight however, so Hipparchus wasn’t able to detect it with his device. When the moon is farthest from the earth, it is at “apogee” and when it is closer, it is at “perigee.” You can remember this by recalling that both apogee and away start with an a.
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