‘Blue Moon’ on Friday: Where Does the Phrase Come From?
On Friday morning at 6:43 am EDT, astronomy enthusiasts can witness a lunar event that takes place only once in a blue moon: a blue moon.
By its modern definition, a blue moon is the second full moon in a calendar month, an astronomical phenomenon that occurs about once every 2.7 years. (The calendar year is 365.24 days long, while a lunar month is 29.53 days; that leaves about 11 extra days after a 12-moon cycle. Every three years or so, that adds up to an extra full moon in a calendar year.)
Read the article “‘Blue Moon’ on Friday: Where Does the Phrase Come From?” on csmonitor.com.