For those interested in astronomy, Saturday (June 30) could be a landmark day, for they will be in a position to cite a `Blue Moon’.

According to a Sydney Morning Herald report, the “Blue moon” is a quirky astronomical term used to describe the second full moon in a calendar month, an event which occurs only once every two and a half years.But it hasn’t always been this way. Up until the 1940s, the term blue moon was used to describe the third full moon in a season.However you define it, a blue moon isn’t a common event. On average they occur once every two and a half years, which probably led to the term ‘once in a blue moon’.

So if the moon doesn’t change colour, why use the term ‘blue’?

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