The moon appears so large, a full seven percent larger, because its orbit around the Earth is oval rather than perfectly round.
– When the moon is closest to the Earth, and it coincides with a full moon, it's called a 'supermoon,' says Peter Linde, associate professor of astronomy and president of the Swedish Astronomical Society.
In addition, the full moon will be low on the horizon in late summer, affecting its perception.
– You have reference points with trees or buildings. So there is an optical illusion that makes it look even bigger, Linde explains.
The best chance to see the phenomenon is in Norrland.
– The chances of seeing it are quite high the further north you go in the country, says SMHI meteorologist Emma Härenstam.
If you're lucky, you may also catch a glimpse of the planet Saturn, which will appear as a faint star just above the moon.
– All in all, it will be a beautiful spectacle. It's much nicer to see the moon near the horizon than when it's high in the sky, says astronomer Linde.
The occurrence of two full moons in the same month is called a "blue moon". The last time was on August 1, and it was also a supermoon. The "blue supermoon" phenomenon, two supermoons in one month, will not occur again until 2037.
– 'Once in a blue moon' is an English saying, and the meaning is not that the moon is blue, but that there are two full moons in the same month, says Peter Linde.