Blue moon 2020: how to see the rare Halloween Hunter’s mini moon this October from the UK - and when is the next one?
The combination of a few lunar phenomena make October’s second full moon a particularly rare one – here’s how to see it
This year’s holiday on 31 October will be accompanied by a bright, full moon, perfect for aspiring werewolves to howl towards.
But the Halloween full moon gets spookier still, and it’s known as a Blue Hunter’s Moon. It will also be a mini moon, meaning it could technically be referred to as a Mini Blue Hunter’s Moon.
Here is everything you need to know about this rare celestial phenomenon.
What is a Blue Moon?
Blue moons are rare enough that they birthed the phrase, “once in a blue moon”, but the phenomenon itself is slightly less exciting.
Rather than the moon actually changing colour, a blue moon refers to when two full moons appear in the same calendar month.
Seeing as the evening of 1 October also played host to a full moon, that means Halloween’s moon is a blue moon.
They occur because the time it takes for the full 12-moon cycle is around 11 days shorter than the Earth’s orbit of the sun, and happen every two to three years on average.
When was the last blue moon - and when is the next one?
The last blue moon occurred in early 2018, and the next one won’t be seen until August 2023.
There will only be six blue moons between now and 2037, although that year will see two of them.
Will the moon actually be blue?
While the title of blue moon doesn’t actually refer to the colour of Earth’s only natural satellite, there are some very specific atmospheric conditions under which it can appear to turn a different hue.
A moon that actually looks blue is a very rare sight, but the Moon can appear blue at any time if the atmosphere is filled with dust or smoke particles of a certain size.
Instances like this can happen following mass volcanic eruptions, such as that of Mount Krakatoa in 1883 or Mount St. Helens in 1980.
What is a Hunter’s Moon?
In recent years, traditional Native American names for the full moons have become more common in modern day parlance according to the Old Farmers’ Almanac - which first published the Native American names for the full Moons in the 1930s.
However, the Hunter’s Moon is not related to this folklore.
The name is instead traditionally given to the first full moon following the Harvest Moon (which this year took place on 1 October), as this is the time of year when humans and animals alike are stocking up on food in preparation for the long winter ahead.
What is a mini moon?
Much coverage is given to supermoons, full moons which can appear bright and larger in the night sky due to the Moon’s elliptical orbit around the Earth bringing it slightly closer to our planet at certain times.
But much less is said about minimoons, the exact opposite of this phenomenon.
It's not hard to see why: with the moon slightly further away from Earth on its egg-shaped orbit, the full moon will likely appear smaller and slightly dimmer as it rises on Halloween night.
The moon of 31 October will actually be the ‘smallest’ full moon of 2020.
When to see the full moon?
As usual, the moon will be perfectly visible to the naked eye come Halloween night, though of course cloud coverage could scupper your chances of seeing it.
At the time of writing, the MetOffice is forecasting an unsettled end to October, so it may be tricky to spot the moon come Saturday.
On 31 October, the moon will rise shortly after sunset at around 4.50pm, and will stay in the sky for the duration of the night.