A spectacular full moon is coming – but it is also dividing opinion

The supermoon at the end of August was also a blue moon – the second full moon in a calendar month (Picture: Danny Lawson/PA)

Next week, on Friday, September 29, skygazers will be treated to another gorgeous full moon – but will it be a supermoon? Opinion is divided.

Here on Earth, we see a supermoon when our natural satellite is closer than normal, appearing up to 14% bigger and 30% brighter in the sky than the faintest full moon of the year.

This is because the Moon travels around Earth on an elliptical orbit, meaning it is slightly oval, not a perfect circle. The point at which it is closest to us is called lunar perigee. The opposite point, when it is furthest away, is known as lunar apogee.

However, there is no internationally accepted distance from Earth at which a full moon earns the title ‘super’, so depending on your point of view – or what you read online and in the papers – next week’s spectacle could be the third or fourth supermoon this summer. Or not super at all.

‘There is no standardised definition of what a supermoon is and a number of different definitions are in place,’ said Dr Greg Brown, astronomer at the Royal Observatory Greenwich. ‘Each organisation will choose, for whatever reason, the definition that they follow.

‘Because of this, various organisations will claim there are two, three or four supermoons this year. They don’t disagree on how far away the Moon is, only on how far away it needs to be to be considered a supermoon.

The Moon at its furthest and closest points in 2020 (Picture: Nasa)

‘Based on the definition that the Royal Observatory Greenwich has adopted, a fixed distance of 360,000 kilometres – about 223,694 miles – the Moon will be just outside of that [next week] and would not be counted as a supermoon.

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‘That doesn’t make other organisations wrong, or indeed us correct, it is simply a matter of preference over the definition.’

Across the Atlantic, Nasa agrees.

‘The coming full Moon will be larger than average, but it will not be the largest full moon of the year – that was at the end of August,’ said Dr Noah Petro, project scientist for Nasa’s Lunar Reconnaissance Orbiter mission.

A plane passes in front of July's Buck full moon — A plane passes in front of July’s Buck full moon (Picture: AP)

No points for guessing why it was given that name – the Harvest moon is the full moon closest to the autumnal equinox, marking the start of the new season and the time during which the summer’s crops are gathered.