When the moon's a balloon

The big ol' moon is going to be bigger, shinier and a tad bit closer to Earth this weekend.

On Sunday evening we earthlings are going to see a "super-moon" rise from the horizon. It is going to be 16% larger and 30% brighter than usual, and will definitely look bigger while it sits on the horizon.

The moon is going to be 356 922km from Earth.

That is 1 362km closer than it was a little less than a month ago and makes it the closest that the moon is going to be to Earth this year.

It is what astronomers call a "perigee", the shortest distance between the Earth and a body during its orbit.

Supermoons aren't that rare. Three are slated for this year. The first was on July 12, then on Sunday, and again next month.

On each of these occasions the moon is full and at perigee, but this supermoon is going to be different.

"This time the moment of full moon will be within minutes of it being closest to Earth," explained the director of the Johannesburg Planetarium, Dr Claire Flanagan.

And according to National Geographic, the timing of the moon this weekend couldn't be better, with perigee occurring only 26 minutes before the moon officially reaches its full phase at 18:10 Universal Time (or 6.10pm) on Sunday.

At that time the moon will be straight overhead in the sky, above the Indian Ocean. Such timing won't occur again until 2034.

But don't be surprised if you can't spot the difference from other full moons. The difference in distance between Earth and the moon compared to last month's supermoon will be no more than a few hundred kilometres - something the human eye can't really detect.

For moon-watchers and photo-hounds the best time to view the big cheese is just after sunset on Sunday, just as the full moon begins to rise.