It hasn’t happened on New Year’s Eve since 1990 and won’t happen on one again until 2028. Tonight, look up into the sky and see a rare phenomenon, the second full month in the same month, a Blue Moon. Assuming the night is clear, and that’s a big assumption here in Chicagoland, I’ll be looking high in the sky.
Why is this a rare thing? Because most years only have 12 full moons which occur approximately monthly. However, the solar calendar year contains about eleven days more than the lunar year. After a period of time those days add up to an extra cycle giving us 13 full moons every two or three years.
Will it look blue? No, but it should be brighter than usual. Tonight the earth will be at a point where it comes closest to the sun. Both the earth and the moon receive more sunlight, making the moon brighter this month. It will appear about 7% larger than average. And yes, that’s correct, we are now closer to the sun even though it is freezing cold here. That is because the northern hemisphere is tilted away from the sun giving us shorter days and less heat.
Then why is this called a Blue Moon? It can be traced to a 55 year old mistake. It’s use comes from a misinterpretation of the Maine Farmer’s Almanac in an article in the March 1946 Sky and Telescope Magazine. Widespread adoption of the definition of a “blue moon” as the second full moon in a month followed its use on the popular radio program StarDate on January 31, 1980. What is the traditional use of the term Blue Moon? According to the Farmer’s Almanac it is the fourth full moon in a season, a season being 3 months such as winter, spring, etc.
A safe and happy New Year’s Eve to everyone. See you next year.