Tonight's the night: the 2021 full Harvest Moon will grace our skies in the UK, making it the perfect time to try out some astronomy or even astrophotography.
Unfortunately, for most of us in the UK, the weather might be cloudy this evening. But just in case it's not, read on to find out when you can see the full Moon, what features you can see on the lunar surface and how you can photograph it. We've answered these with the help of Prof Michael Merrifield, an astronomer at the University of Nottingham.
Don't worry if you miss it – there will be one next month. Make sure to check the full Moon calendar for the date of the next one. In the mean time, take a look at the meteor shower calendar to find out when to catch the Draconids, or read our guide to astronomy for beginners.
When is the full Harvest Moon 2021?
The Moon will reach peak 'fullness' at 12:54am on 21 September 2021 in the UK. Though the Moon is technically full for only a moment, you can enjoy great views (weather permitting) for more or less a full day before and after this time.
Why is it called the Harvest Moon?
Full Moons all have a name, and that name is usually related to the time of year.
"It is a tradition to give each of the full Moons of the year a name, and, since we are at harvest time now (at least in the Northern Hemisphere), it is a pretty good way to identify the full Moon with the time of year," says Merrifield.
How often do full Moons happen?
Full Moons happen roughly once every 29.5 days. This is how long it takes the Moon to orbit the Earth once. In fact, the concept of a month was originally based on the length of the lunar cycle – though in our modern calendar, we've adjusted the months to line up with the length of a year.
We normally see one full Moon a month – but because calendar months aren't the same length as lunar months, it's possible to get two full Moons in one month. When there are 13 full Moons in one year, we call the bonus one a 'blue Moon'.
What details can I find when looking at the full Moon?
"It really depends how good your eyesight is! Without a telescope, you might be able to pick out the darker regions called 'mares' or 'seas'. They aren’t, of course, actual oceans – they are expanses of ancient lava flow that have left these dark stains across the Moon," says Merrifield.
"With a pair of binoculars or a small telescope, you ought to be able to start picking out plenty of individual craters. Away from full Moon, looking close to the terminator – where night turns to day on the Moon – should help, as that is where the shadows are longest, helping to pick out these features."
There are a few craters you can pick out by eye on the Moon's surface. If you're in the northern hemisphere, look slightly to the left of the Moon's centre and you'll see a bright crater named Copernicus. To the left of Copernicus, you'll see the Aristarchus crater, and down near the bottom is Tycho.
If you're in the southern hemisphere, the Moon will appear the other way up.
What’s the best way to photograph the Harvest Moon?
When the Moon is full, it's always tempting to pull out your phone and snap a picture – but more often than not, it'll end up as a pale splodge in the sky, and not the impressive sight you can see with your eyes. So is there a good way to take a picture of the full Moon?
"Counter-intuitively, the full Moon is not a particularly good time to photograph the Moon," says Merrifield. "The issue is that we are effectively looking at the Moon at midday, so the shadows are very short – when the Sun is a little lower in the lunar sky, the shadows cast make it easier to pick out the three-dimensional structures of mountains and craters, so you might get a better view of the Moon a week before or after full Moon.
"But it is an impressive-looking thing when full, so worth a try. If you have a zoom lens, do make full use of it. Even a cheap telescope can get a nice shot of the Moon if you point your phone into the eyepiece.
"If you have a fancier camera that allows you to change things manually, reducing the exposure time or stopping down the lens (so setting a higher 'F number') can often prevent over-exposure, which can produce much clearer images."
About our expert, Prof Michael Merrifield
Michael is a professor of astronomy at the University of Nottingham. He studies the formation and structure of galaxies, cosmology, and X-ray and gamma astronomy.