August’s second full moon will light up the skies tonight, and for the third straight time it will be a supermoon.
A second full moon in a month is known as a blue moon – at least by some definitions – though others would dispute this.
The phenomenon is relatively rare – only around 3 per cent of full moons are blue moons, according to Nasa.
Here’s what is meant by a blue moon and how to see it from the UK tonight.
When is the next full moon?
The next full moon falls on Thursday 31 August, reaching its peak in the UK at 2.35am, according to the Greenwich Royal Observatory – the first full moon of the month peaked at 7.31pm on Tuesday 1 August.
These timings mean that it will be most visible overnight from Wednesday.
Astronomy Professor Don Pollacco, from the University of Warwick, advises stargazers: “To see the full moon, look East after Sunset. If you have a clear horizon it should be obvious.
“The moon is so bright that we can see it when it’s not particularly dark or even if the weather isn’t particularly clear. It will be visible all night and set in the West around sunrise.”
What is a blue moon?
Just for the avoidance of any doubt, a blue moon doesn’t mean it will actually turn blue.
Instead, a blue moon is a phenomenon that occurs because full moons take place every 29.53 days – which means the lunar “year” of 12 cycles lasts just over 354 days.
The lunar year therefore comes in almost 11 days shorter than the time it takes the Earth to orbit the sun, resulting in some years having “extra” full moons.
A blue moon is traditionally defined as the third full moon in an astronomical season containing four full moons.
Astronomical seasons begin and end at the year’s two solstices and two equinoxes – there are usually three moons in each astronomical season, making 12 in total for the lunar year.
Given that we use the standard Gregorian calendar, this definition of a blue moon can be a little confusing for most people, so there is a simpler option.
A blue moon therefore more commonly (and erroneously, according to the Greenwich Observatory, which blames such fake news spreaders as 80s-era Trivial Pursuit) denotes the second full moon in a calendar month – this is what’s happening in August.
The origins of the term blue moon are mysterious, with the observatory suggesting that it could be a mispronunciation of “belew,” meaning “to betray” – denoting the Moon deceiving observers by arriving too early in the seasons.
What is a supermoon?
A supermoon occurs because the moon moves closer to and further away from the Earth at different points in its elliptical orbit.
This means there can be a difference of up to 30,000 miles in its distance from our planet. The closest point is called the perigee, and the furthest is called the apogee.
If the moon becomes full when it is reaching or approaching its closest perigee, it is considered a supermoon.
According to US astrologer Richard Nolle, it should be within 90 per cent of its closest approach to Earth in order to earn the label – around 225,000 miles.
According to the Natural History Museum’s website, supermoons appear so bright because they “cast about 30 per cent more light on the planet than when the moon is at its dimmest”.
2023 full moon schedule
Here is the full calendar of full moons for 2023, along with the times they peak:
- 6 January (11.07pm)
- 5 February (6.28pm)
- 7 March (12.40pm)
- 6 April (5.34am)
- 5 May (6.34pm)
- 4 June (4.41am)
- 3 July (12.38pm)
- 1 August (7.31pm)
- 31 August (2.35am)
- 29 September (10.57am)
- 28 October (9.24pm)
- 27 November (9.16am)
- 27 December (12.33am)
How often do supermoons occur?
Supermoons tend to fall around three or four times a year, and they come in a row. This is the third of four consecutive supermoons in 2023, with the final one coming in September.
The phenomenon is therefore relatively common. However, sometimes the heavens align to such an extent that we see an extra-supermoon (not an official term).
In November 2018, for example, the moon reached its fullest point within about two hours of its perigee, according to Nasa. As a result, it appeared as much as 14 per cent bigger and 30 per cent brighter than it would have at the apogee.
This made it the largest supermoon since 1948 – and we won’t see a full moon as close to earth again until 25 November, 2034.
