July's supermoon will appear full for up to three days, according to Nasa.
Known as a Buck Moon, it will be closer than normal in its orbit around the Earth.
This is because the Moon's orbit is not a perfect circle due to the Earth's gravitational pull; instead it is elliptical, like an elongated circle or oval.
Because of this, there are times in the Moon's 27.32-day orbit when it is closer to the Earth and other times when it is further away.
A supermoon happens when the Moon is at the closest point to Earth in its orbit and also in its full moon phase.