You might use the expression ‘once in a blue moon’, but do you have any idea what one actually is?
Because when the moon rises tonight at around 21:00, it will be a blue moon, but not because it is remotely blue!
It will be a blue moon because it is the second full moon this month.
So, provided that it is possible to catch a glimpse behind the endless clouds, it will appear exactly the same, but it is something of a unique experience – hence the expression.
Not until 2018
The term ‘blue moon’ derives from the time when it was known as the ‘Blewe’ or ‘traitor’s moon’, when two full moons would occur during Lent and force devout Christians to continue abstaining from eating certain foods for another month.
A blue moon occurs once every two to four years. The next one will take place on 31 January 2018.
