ELI5: Explain Like I'm 5

Lune of Hippocrates

Have you ever seen the moon when it is shaped like a crescent? It looks like a curved line or a banana, right? That shape is called a lune. Now, the lune of Hippocrates is a special type of lune that is named after a man named Hippocrates who lived a long time ago.

Hippocrates was a very wise man who knew a lot about medicine and the human body. He was interested in finding a way to measure the different times of the year when the daylight and nighttime were equal. He found a pattern in the movement of the moon and the sun, which helped him create the lune of Hippocrates.

So, can you imagine drawing a banana shape using two circular arcs? This is how the lune of Hippocrates looks like. One arc is the shape of the moon, and the other one is the shape of the sun. When the light part of the moon (crescent) lines up with the curved arc of the sun, it means that it is the time of the year when the night and day are equal in length. This time is called the equinox, and it happens twice a year, in March and September, when the spring and autumn begin.

Therefore, the lune of Hippocrates is a way to show how the sun and the moon interact to create the changing seasons, and how Hippocrates was able to measure this accurately.