Moon Illusion

Is the moon really bigger on the horizon?


No, but it looks like it is.
  • If you take a photo, hould your thumb out or hold a ruler out at arms length for both a moon on the horizon, and then hours later when it is up high in the sky, you will see it is the same size, though your eyes/brain will say it is now smaller.
  • It is not the earth's atmosphere that makes the moon look larger, though that was the common bielef started centuries ago.
  • It is an optical illusion that makes the moon look bigger. It is because on the horizon there are usually objects we know are big, such as trees, buildings and clouds, and they are looking quite small. We know these objects down low on the horizon are far away.  The moon passes by these objects only briefly at a moon rise or set and 'looks' much bigger then the next view we are more used to. When the moon is high in the sky it is close to these same large objects (trees, buildings or clouds), only these objects look much larger now and look much, much bigger next to the moon as a reference- and so the moon looks much, much smaller in comparison. This tricks our brain into thinking the moon is now further away.
    See Illistration: Which moon is bigger? Measure them and find out (put a ruller on your screen).
  • However, here's the most likely reason your eyes and brain come up with the conclusion that the moon is much larger on a particular night. Usually when you notice a moon that you think is much larger, you are viewing the moon over a landmark that you’re familiar with and usually much closer to, but on the large moon occasion, you are much further away from that landmark. The moon stays the same size but the landmark shrinks the further away you go from it - thus making it look like the moon is getting bigger. Have a look at this example below [coming soon!]