‘Supermoon’ brightening up skies for stargazers
Image copyrightDANNY LAWSONSkywatchers have begun catching glimpses 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. This supermoon is the last opportunity to see one in 2017.
Image copyright: SEAN QUINNTo observers, the Moon will appear about 7% larger and 15% brighter, although the difference is barely noticeable to the human eye.
Robert Massey, of the Royal Astronomical Society, said this supermoon will appear brightest at midnight – when at its highest point above the horizon. BBC weather presenter Ben Rich says there should be opportunities to see the supermoon with some clear spells for most parts of the country, although there will also be areas of clouds.
Last year the Moon made its closest approach to Earth since 1948 – it won’t be that close again until 25 November 2034.
Nasa has called this weekend’s sighting the first in a “supermoon trilogy”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.
This 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.
Image copyright: KARLI FRANKLINMoon illusion
Mr Massey said the “most spectacular views” would be during moonrise, on Sunday afternoon, and moonset, on Monday morning. This is because an optical illusion, known as the Moon illusion, makes it look unusually large when it appears close to the horizon.
Mr Massey said: “It’s a nice enough phenomenon.
“You won’t necessarily think that it’s huge. It will appear a bit bigger than usual, but don’t expect it to look five times bigger.”
Image copyright: OWEN HUMPHREYS/PAThis 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.
Read more at www.bbc.co.uk
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