When I was a kid, one of my mum's most commonly-uttered phrases was 'There'll be a blue moon tonight.'
You know the sort of thing; you ate up all your broccoli without complaint or tidied your room without being asked, and she'd ruffle my hair and mutter 'There'll be a blue moon tonight'.
Except tonight there actually WILL be a blue moon, and no-one has had to eat a plate of greying broccoli or tidy up their toys to make it happen, as far as I am aware.
Here's what the Metro says about this strange phenomenon:
That rare lunar phenomenon that everyone talks about is about to happen.
But newsflash: it’s not going to be blue. And it’s not actually that rare. Oh.
A blue moon occurs when there are two full moons in a month, and that happens around every three years.