Tonight’s Blue Supermoon – What Is It?

Moon Set Behind Cascade Mountain, Banff. October 5, 2012.

Tonight, August 30-31, 2023, the full moon will be bigger and brighter than most full moons. So go out and look. I love the night sky, so in my book, any time spent looking up at the night sky is time well spent, supermoon or not.

There are two definitions of a “Blue Moon” and the most recent is the result of a mistake in a Sky and Telescope magazine article back in 1946. (Both Blue Moon definitions arose out of religious calendars and/or folklore, not science.)

Blue Moons are not hugely rare. They happen every 2 or 3 years. Our last Blue Moon was August 21-22, 2021, and our next Blue Moon is tonight.  After tonight, the next Blue Moon will be August 19, 2024 and the next Blue Supermoon will be in January 2037.

This week’s full moon is a “monthly” Blue Moon because it is the second full moon this month. A monthly Blue Moon is the more recent definition of a “Blue Moon” thanks to that 1946 article.

The original, pre-1946 definition of a Blue Moon is a “seasonal” Blue Moon which is the third Full Moon of an astronomical season that has four Full Moons.

This week’s full moon is also a supermoon because it is closer to earth (which is around perigee when the moon’s orbit takes it closer to the earth than usual). When the full moon is farther away it is a micromoon (which is around apogee when the moon’s orbit takes it farther from the earth than usual). A supermoon is 14% bigger and 30% brighter than a micromoon.

The term supermoon is not scientific and was created in 1979 to create a little more hype for full moons near perigee and get more people outside to look at the moon.

A Blue Moon has nothing to do with the color of the moon. On rare occasions the moon will look blue thanks to an abundance of tiny particles in the atmosphere that are slightly wider than 900 nanometers. That usually happens after volcanic eruptions or large wildfires. Those 900+ nanometer particles deflect a lot of light in the red wavelengths, leaving a higher percentage of blue light rays to reach our eyes. So the moon looks blue.

FYI: Most photos or videos of the moon looking blue in color were created using blue filters over the camera lens, or by digitally manipulating the photos using software. This is sometimes done for advertising photos when some art director wants a blue colored moon. It also happens in movies and TV shows.


How to Photograph Tonight’s Blue Supermoon

What Is a Blue Moon and When Is the Next One?

Blue Moon: What is it and when is the next one?

Blue moon? What is it and when is the next one?