Blue Moon

• Every three years there are two Full Moons in one calendar month.
• In modern times, the second Full Moon has become known as a ‘Blue Moon’.

Description

• Because the Moon cycle takes 29.5 days to complete a full orbit, every 3 years there are two Full Moons in one calendar month.
• However, as February only has 28 days, sometimes it has no Full Moon at all.

Once in a Blue Moon

• This phrase is used to mean an event that occurs very rarely.
• The older meaning of ‘once in a Blue Moon’ derives from the rare occurrence of a blue tinged Moon due to high altitude dust.