'Supermoon' brightens up skies for stargazers

Skywatchers have enjoyed spectacular views of this month's "supermoon" - when the Moon appears larger and brighter in the sky.

The supermoon phenomenon happens when the Moon reaches its closest point to Earth, known as a perigee Moon.

The Moon circuits the Earth in an elliptical or oval orbit - a supermoon occurs when the perigee Moon is also a full Moon.

The supermoon was the last opportunity to see one in 2017.

To observers, the Moon appears about 7% larger and 15% brighter, although the difference is barely noticeable to the human eye.

Last year the Moon made its closest approach to Earth since 1948 - it will not be that close again until 25 November 2034.

Nasa has called this weekend's sighting the first in a "supermoon trilogy", external over the next two months, with others to come on 1 January and 31 January.

December's full Moon is traditionally known as the cold Moon.

The full Moon on Sunday afternoon - when it sits opposite the sun in the sky - was 222,761 miles from Earth, closer than its average 238,900 miles.

This Moon's elliptical orbit means that its distance from Earth is not constant but varies across a full orbit.

But within this uneven orbit there are further variations caused by the Earth's movements around the Sun.

These mean that the perigee - the closest approach - and full moon are not always in sync.

But occasions when the perigee and full moon coincide have become known as supermoons.