Why does the Moon look bigger on some nights?

Have you ever seen the Moon rising over the rooftops, big and golden like a giant lantern? Later that night, high in the dark sky, it looks smaller and paler. Tonight you could peek out your window and see how the Moon looks for you.

So why does the Moon look bigger on some nights? Let's follow the Moon on its journey and find out together.

The Moon travels all the way around our Earth, again and again, because Earth's pull keeps tugging it along. We call this path an orbit, which means the loop the Moon follows around us.

The Moon's orbit is not a perfect circle. It's a tiny bit squashed, like a hoop someone pressed gently into an oval. So on one side of the orbit, the Moon swings closer to Earth, and on the other side it drifts farther away.

When the Moon reaches the close part of its orbit, it truly looks a bit bigger in the sky. It works like a ball that grows bigger to your eyes as a friend carries it toward you. The change is small, though, so it's hard to spot just by looking.

Now think about that giant golden Moon rising over the rooftops. Down low, it sits right beside trees, houses and hills, things you know are big. Do you think the Moon has come closer to you, or is something else going on?

Here's the surprise: the low Moon is no closer and no bigger than when it's high above. Your eyes and brain are playing a trick on you. We call this trick an illusion, which means something that looks one way but is really another.

Nobody knows for sure exactly how this illusion works. One good idea is that your brain compares the Moon with the faraway rooftops and trees, and decides it must be huge. High up in the empty sky, there's nothing beside it to compare, so the Moon looks smaller again.

Sky watchers check the illusion with one little fingernail. They hold an arm out straight and cover the low Moon, then try again when the Moon is high. Both times, the fingernail covers the Moon exactly the same.

A rising Moon looks huge because an illusion tricks your brain when the Moon sits low beside rooftops and trees. And on nights when its oval orbit swings it closer to Earth, the Moon really does look a little bigger.

Far above the quiet rooftops, the Moon climbs into the dark sky, small and silver now. On and on it sails along its oval orbit, around and around our Earth.