Last Sunday night you may have seen something in the sky that only happens once every 18 years. It was a super moon.

A super moon looks a lot bigger and about 30 times brighter than the moon normally is. That’s because it’s closer to the Earth than normal. Its official name is a super “perigee moon,” but people just call it “super moon.”

The above picture was taken in my garden at around 2am. Later the moon turned red but the sky wasn’t so clear.

The moon moves around the Earth in an oval shape, not a perfect circle, so there are times when the moon is closer to the Earth or farther away from it. On Saturday, the moon was really close to the Earth.

People all over the world could see the super moon on Saturday, including Australia, Russia, Canada and the United States. According to NASA, the last time a super moon like this was visible was 1993.

Could you tell that Saturday’s moon was different from regular full moons? It was very tricky, because the moon was only 14 per cent bigger than usual. Because the moon is so far away, it is hard to tell the size difference without a telescope. In fact, many people who saw the super moon last Saturday said they didn’t think it looked that much larger than normal.

The biggest difference between a super moon and a regular full moon is how bright it is. A super moon illuminates the ground and lights up the Earth. Before electricity was invented, super moons would have been very helpful for seeing at night in the dark.

Sometimes a full moon looks even larger because it is close to the horizon. The horizon is the line where the earth and sky meet. Objects like trees and buildings on the horizon look like they are close to the moon and make the moon look bigger–that is called the “moon illusion.”