By now you have probably heard about today's supermoon.
It happens because the moon's orbit around Earth isn't a perfect circle, so sometimes it's further away from us, and sometimes it's closer.
But remember: The change in distance (and therefore size) happens gradually over the month, so it's not like the moon is going to appear much bigger today than it did yesterday.
The moon is so far away and so small in the sky that, even when it's a supermoon, you're unlikely to be able to detect any change by eye.
Astronomer Phil Plait explained on Slate in 2013:
While this is technically true, you’d never notice the difference in size or brightness by eye. The full Moon will look pretty much like every other full Moon you’ve ever seen. Which is to say, big, bright, beautiful, and completely worth your time to outside and see! But Supermoon? Not so much.