On October 31st we will have a monthly blue moon. It is a rare astronomical phenonema that only occurs every two to three years. But what is it? A monthly blue moon is the second full moon when you have two full moons in the same month.
There is also a second kind of blue moon that is a little rarer.
A seasonal blue moon is a blue moon that is the fourth full moon in a season. They also occur every two to three years. Over 1000 years, there might be 450 monthly blue moons compared to 400 seasonal blue moons. Both are commonly just called a blue moon.
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We have two definitions of a blue moon because of a mistake.
The real blue moon is a seasonal blue moon. The monthly blue moon was created by James Hugh Pruett, an amateur astronomer. He wrote an article in Sky & Telescope magazine in 1946 that described a blue moon as the second blue moon in a month. He had misinterpreted the real definition. His definition then was quoted on a radio show, included in Trivial Pursuit, and generally became accepted.
So, no, unfortunately, the moon’s color will not change blue.
Although, the moon can sometimes change to the color red. That is called a blood moon . It happens when there is a total lunar eclipse. During the eclipse, the earth casts a shadow over the moon. The moon doesn’t get completely black because light from the atmosphere shines on the surface of the moon. The light makes the moon look red. The next blood moon is May 26, 2021.
This Halloween, take a moment to appreciate the moon.
No, it will not be blue, or red, or any fancy color. And no, technically it is not a blue moon. But it is beautiful. And we can all use an excuse to stop and appreciate our beautiful solar system.
h/t: timeanddate.com
Last Updated on October 15, 2020 by Jennifer Seaton
