The last supermoon of 2023 rises tonight, just after sunset. And it’s possibly the Moon with the most well-known name of them all; the Harvest Moon. But when is the best time to see the supermoon from the UK? Which constellation will the Moon be in? We’ve rounded up everything you need to know below.
Why not make the most of the longer nights with our full Moon UK calendar and astronomy for beginners guide? And in case you missed it, veteran astronomer Pete Lawrence has put together a comprehensive guide to how to take great pictures of the Moon; all you need is a smartphone to get started.
When can I see the Harvest supermoon in 2023?
The Harvest supermoon will be visible tonight, 28 September 2023, in the UK and around the world. If you’re unable to see 2023’s last supermoon at its peak, it will also appear full the night after on 29 September.
The Harvest Moon will rise in the east at 6:41pm on 28 September (UK time) and set exactly 12 hours later, in the west at 6:41am on 29 September. This is thanks to our proximity to the autumn equinox.
The Sun will set just a few minutes earlier at 6:45pm, so the Moon will rise into a twilight sky.
If rainstorms, clouds, or Storm Agnes hampers things, or you are unable to see the full Harvest Moon at its peak, it will also appear full tomorrow night on 29/30 September.
When is the best time to see the Harvest Moon?
Weather permitting, the best time to see the full Harvest supermoon is soon after rising, while the Moon is still low on the horizon. At this time, although not the exact moment of full, it may appear orange in colour, and larger thanks to the effects of the Moon illusion (more on that below).
The Harvest supermoon this year will reach peak illumination at 9:57am on 29 September, however, this is after the Moon has set in the northern hemisphere. The moment of full illumination will last for just a moment, and this moment has a name: syzygy. It occurs when the Earth is directly between the Sun and the Moon, in a straight line.
Even if the Moon was above the horizon at this time, our human eyes wouldn’t be able to notice much in terms of increased brightness. So with the weather looking grim, you’re better off stealing a glimpse where you can in between clouds, when the Moon rises this evening.
Will the Moon look orange?
The Moon may look more yellow, orange or even reddish when near the horizon. The orange colour is down to a process known as Rayleigh scattering. When the Moon is near the horizon, you're looking through more of the Earth's atmosphere, and light has a longer distance to travel.
The more atmosphere, the more those colours with shorter wavelengths, like blue, get scattered. The colours with longer wavelengths, like red, orange, and yellow, are left behind – and that’s why the Moon takes on an orange hue when it’s near the horizon.
What is the Moon illusion?
The Moon can look bigger when it’s nearer the horizon, and this is what we call the ‘Moon illusion’.
Although it’s not actually bigger; it’s just our human eyes playing tricks. Most people agree that it’s a result of the way we perceive the Moon in context to other things. In this case, our brains will compare the Moon with distant objects on the horizon (such as foliage, hills, cityscapes, buildings, or masts) and fool us into thinking it’s much larger.
Add a supermoon to the equation, and the Moon will look bigger still.
Why is it called the Harvest Moon?
Also known as the Corn Moon in the Americas, the nomenclature of the Harvest Moon is somewhat special. It’s the only full Moon name that’s determined by the equinox, and is so-called because it’s the full Moon nearest the equinox (some people refer to the Harvest Moon as the first full Moon after the equinox). That means that sometimes, the Harvest Moon can fall in October.
The Harvest Moon is special for another reason; there’s no interval between sunset and moonrise, making it the earliest full Moon rise of the year.
The Harvest Moon is so-called because prior to the invention of floodlights, the Moon would cast a welcome light over farmer’s crops, allowing them to extend their working day and continue harvesting past sunset. For a similar reason, the Harvest Moon is also sometimes called the Corn Maker Moon or the Barley Moon.
What constellation will the Moon be in?
Yesterday, 27 September 2023, the Moon was in its waxing gibbous phase and was 2.7 degrees south of Saturn in the constellation Aquarius. Then a few days after full on 2 October 2023, it will pass 3.4 degrees north of Jupiter and 2.9 degrees north of Uranus later that same day.
Tonight, when the full Harvest supermoon rises on 28 September 2023, it will be in the constellation Pisces, just below The Circlet; a ring of stars that make up one of the fish’s heads. Look towards Aquarius, and you’ll be able to pick out Saturn near the binary star system Iota Aquarii, while the mighty Jupiter is visible between the constellations Aries (above) and Cetus (below).
Is the Harvest Moon in 2023 a supermoon?
Yes, the Harvest Moon in 2023 is a supermoon. It’s also the fourth and final supermoon of 2023!
Supermoons are an unofficial designation for when the Moon is 360,000km or closer to Earth in its orbit, and we'll often see two or three full supermoons in a row. In 2023, the July full Moon, the Buck Moon, the first full Moon in August the Sturgeon Moon, and last month’s Blue Moon, were all supermoons.
What causes a supermoon?
The Moon has an elliptical (oval-shaped) orbit around the Earth, so depending on where it is in that orbit, its distance from us changes over time. When the full Moon coincides with the perigee – the point in its orbit when it comes closest to the Earth – and providing the Moon is closer than 360,000 km to the Earth, we get a supermoon.
Although an unofficial designation, it's a term that has gained in popularity over recent years, and doesn’t look set to disappear any time soon.
Visually speaking, a supermoon appears around 7 per cent larger and around 15 per cent brighter than a regular full Moon
At the opposite end of the spectrum, when a full Moon is at its furthest distance in its orbital path around the Earth (called the apogee), the Moon appears smaller, and has (again, unofficially) been termed a micromoon. If we compare a supermoon to a micromoon, a supermoon looks around 14 per cent bigger and 30 per cent brighter.
Is a full Moon always at 100 per cent illumination?
Not always! Sometimes a full Moon will only appear 99.9 per cent illuminated. This is because the Moon orbits the Earth at a slightly inclined angle of 5 degrees, when viewed in relation to the Earth’s orbital plane (called the ecliptic). If the full Moon phase occurs when the Moon is above or below the ecliptic, then that angle reduces the percentage of illumination by a small amount.
How often do full Moons occur?
Full Moons occur every 29.53 days (29 days, 12 hours, 44 minutes and 3 seconds, if you want the exact figure). This is how long it takes the Moon to orbit the Earth and complete one phase of the lunar cycle, as measured from new Moon to new Moon. Another name for this is one synodic month.
There are usually 12 full Moons in a year, however this year we have 13. This is because the lunar cycle takes a little under one calendar month, which occurs around every two to three years. The extra moon this year was last month at the end of August, the Blue Moon.
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