Astronomers are in for a treat as 2018 gets under way, with the arrival of a blue moon at the end of January. According to tradition, when two full moons appear in the same calendar month the second is termed a “blue moon”.
It is the celestial phenomenon that gave rise to the phrase “once in a blue moon”. The last one took place back in July 2015 . Even though it is called a blue moon, there’s no colour change in store for our lunar neighbour. The moon won’t suddenly appear with a blueish tinge.
In certain situations (such as the eruption of the Krakatoa volcano in 1883) dust particles in the atmosphere can scatter red light. That makes the moon reflect the blue light, and appear to us down on Earth as if it’s glowing blue.
Here’s everything you need to know about 2018’s rare lunar spectacle.
When will the blue moon take place?
January’s first full moon will take place on the night of New Year’s Day or the morning of January 2nd.
But the second, the blue moon, will take place on the night of January 31.
What’s more, on the night of January 30, the moon will reach the closest point in its orbit, technically making it a supermoon the night before it becomes a Blue Moon.
What is a blue moon?
(Image: Stefano De Rosa)
It’s the rare moment when a second full moon appears during one calendar month, although its traditional meaning is slightly different. A lunar month lasts about 29.5 days, whilst human months last anything between 28 and 31 days.
Occasionally, this means that a full moon can be seen twice in a month – which is referred to as a blue moon.
How do I see the blue moon?
(Image: Getty)
When it gets dark, go outside and look up. You won’t be able to miss it. Weather permitting, the moon will be round and full, allowing smartphone snappers to get a great image. As we get closer to the date, we’ll know more about weather conditions and possible cloud cover that could interrupt the view.
Where does the phrase blue moon come from?
Traditionally, the blue moon refers to an “extra” lunar cycle taking place in a year. Normally, a year would have 12 moons, but when a moon appears for the 13th time – an unusual occurrence – it was referred to as a “belewe” moon, which means betrayer.
The earliest English language reference is thought to be found in an anti-clerical pamphlet written in 1528.
