What is a blue moon, a notable astronomical phenomenon scheduled to occur on Sunday?

It’s a history written in the diaries of an astronomy lover. On the evening of this Sunday, August 22, it will be possible to observe the “blue moon”, a relatively rare astronomical phenomenon. Be careful, however, those who expect the star to change color will be disappointed… The moon will still be white, or at best slightly yellow.

What is a blue moon?

The term “blue moon” actually refers to the second full moon of a month with two full moons, or the third full moon of a season with four full moons. This is the second formation that will be possible to observe on Sunday, August 22.

To fully understand the phenomenon, you must know that the cycle of the moon is 29 days, 12 hours and 44 minutes. Every 29.5 days or so, we can see one full moon, or one full moon a month most of the time. But in the end, there are 11 more days in the calendar year compared to the lunar cycle. As a result, it is possible to observe two moons every two or three years. If you miss Sunday, you will have to wait until August 2023.

Where does the term “blue moon” come from?

But why was the color blue stuck to this phenomenon? At this point, no specialist gives a clear and logical explanation. In a pamphlet dated 1528 and hostile to the British clergy, we find the phrase “If they say the moon is blue, we must believe it is true,” editor’s note).

Another track in Indonesia in 1883 where the eruption of the Krakatoa volcano and the ash cloud that followed caused a blue-tinted moon to appear for a few minutes. Unless the explanation is found on the Quebec side, where the term “blue moon” allegedly comes from a bad imitation of the French term “double moon”, which would have become “blue moon”.