The term ‘supermoon’ carries with it a heavy dose of expectation, with the coined term leaving unaware individuals with the idea that the moon will appear much bigger and brighter than it normally is in the sky.
While the supermoon is indeed at perigee – that is, at the closest it will be to the Earth in that particular orbit around our planet, the difference in size as seen to the naked eye from Earth is unfortunately rather small.
A supermoon occurs when the moon is at perigee and at syzygy at the same time.
The moon is at syzygy every new moon and every full moon, with syzygy referring to the straight-line configuration between the sun, the Earth and the moon. Sometimes, the closest point to Earth in the orbit of the moon occurs when it is in the full moon phase, and this coincidence is called a supermoon.
There is unfortunately nothing really super about the supermoon however, as although it does indeed change its distance from Earth across its orbit, the closest it can reach is still some 350,000km away, and the average orbit distance is around 375,000km away from Earth.
The difference in size, however, can be noticed through a telescope if prior knowledge of the size of the normal full moon through a telescope is known.