The full moon on Saturday appeared to be unusually big. In fact, it was what's known as a supermoon.

That's the nickname for full moons that happen when our celestial neighbour is relatively close to Earth. That distance varies because the moon follows an elliptical orbit. When it's close and full, it appears bigger and brighter than normal, although in fact the difference can be hard to detect.

If you saw Saturday's moon close to the horizon it may have seemed huge, but that's just an illusion caused by its position in the sky.

Two other full moons this summer, on Aug. 10 and Sept. 9, are also supermoons.

It's not all that unusual to have a supermoon. There were three in a row last year.