If you go out on a clear night when it’s the full moon, you may notice how gigantic the Earth’s satellite looks when it’s near the horizon. But, in fact, that moon is the exact same size as every other time as you’ve ever seen it in the sky. You can test this by holding your thumbnail at arm’s length and comparing it to the size of the Moon when it is near the horizon and high in the sky, and you’ll see it doesn’t change size. Photographs of the Moon at different elevations also show that its size remains the same. In fact, it plays a trick on your brain which called the “Moon Illusion”. This illusion has been known since ancient times, and an explanation of this optical phenomenon is still debated.

The moon illusion is subtle for some and dramatic for others (including me). A small fraction of people even don’t see it.

Yesterday, I stumbled upon a YouTube channel named The Science Asylum. In this channel, physicist Nick Lucid covers some popular science subjects. For example, the video below, titled “How Far Away Is The Moon?” explains the distance between the Earth and the moon, and how our brains aren’t good at dealing with the big numbers.