What is a Harvest Moon, and and are they really worth the hype?
Harvest Moon is the name given to the full Moon closest in date to the first day of autumn, known as the autumn equinox.
The autumn equinox is when day and night are the same length.
The last Harvest Moon occurred on 29 September 2023 and the next will occur on 18 September 2024, rising at 19:28 BST (18:28 UTC).
The 2024 Harvest Moon will also be a supermoon, and the second of 4 supermoons in a row at the end of 2024.
What’s more, the 18 September full Harvest Moon will also undergo a partial lunar eclipse.
Find out how to see the Harvest Moon, heralding the return of autumn, and find out when the next full Moon is visible.
If you want to capture the event, read our guide on how to photograph the Harvest Moon.
Origins of the name Harvest Moon
A Harvest Moon’s proximity to the September equinox means that the rise times for the near-to-full phases of the Moon are nearly the same on the days before and after.
So, the Harvest Moon is so-called because the difference in rise times from one evening to the next after this date is the smallest for the year.
This means the bright, fuller phases of the Moon appear at approximately similar times, lighting the way to collect the harvest.
Indeed, it was the abundance of bright early-evening moonlight on those consecutive days that traditionally lit the fields for collecting the harvest.
Measure the Harvest Moon
A good exercise is to note the rise time of the Moon on in the days before and after the Harvest Moon, calculating the differences.
Waiting for the fuller phases of the Moon to rise is a great way to experience the visual effect of the Moon illusion, which makes these phases appear enormous when close to the horizon.
You can also observe the next full Moon after the Harvest Moon and you should see a similar pattern in rise times for its fuller phases.
The period close to the March equinox represents the opposite situation, with the difference between successive moonrises for the fuller phases of the Moon being the largest of the year.
A good experiment during the Harvest Moon is to make a note of the rise times for the Moon from the date of the full Moon onwards (find them at www.timeanddate.com/moon) and calculate the difference.
Try to remember to do this next March too, when the difference is greatest.
Is a Harvest Moon bigger?
Some believe the Harvest Moon is much bigger or brighter than other full Moons in the year. This isn’t true though.
This belief may have come about due to a complex optical illusion that makes the Moon look bigger when it’s lower down near the horizon.
How to observe a Harvest Moon
Around the time of year that the Harvest Moon appears, the Sun goes down almost due west, so the full Moon will be rising near to due east.
As the Moon rises, see if it has a wonderful ochre red colour, especially when it’s low on the horizon.
This is an effect of the Moon’s light being filtered, as it travels through more of the Earth’s atmosphere than when it’s overhead.
Since red light is scattered least by the Earth’s atmosphere, the Moon takes on this lovely red colour.
Find out more about this in our guide on why the Moon sometimes looks orange.
The lower and less built-up your horizon, the better your chance of seeing the Harvest Moon rising in all of its glory – a fantastic sight that heralds the start of autumn.
Pictures of a Harvest Moon
Below is a selection of images of Harvest Moons captured by BBC Sky at Night Magazine readers and astrophotographers.
If you manage to capture an amazing image of the Moon, don’t forget to send us your images or share them with us via Facebook, Twitter and Instagram.
