Rare seasonal “Blue Moon” rises tonight

This month we will see a Full Moon on August 22, 2021, known to some early Native American tribes in the northeastern United States as the Sturgeon Moon. The name was given to the Moon because the large sturgeon in the Great Lakes and other large lakes were easier to fish at this time of year. But that’s not all! We are also fortunate to see a Blue Moon!

We’ve all heard the phrase “once in a blue moon,” which usually refers to something that rarely happens. Blue moons occasionally occur in the night sky of Earth, giving rise to this phrase. But what is a Blue Moon?

Well, we have two types of blue moons – monthly and seasonal.

A monthly Blue Moon is the second Full Moon of a calendar month with two Full Moons. Then there is a blue moon season – the third full moon of an astronomical season that has four full moons.

In astronomy, a season is the period of time between a solstice and an equinox, or vice versa. Each season – winter, spring, summer, or fall – lasts three months and typically has three full moons, spaced approximately 30 days apart. Since the June full moon came just a few days after the June (summer) solstice, we will see four full moons during the current summer season, which ends at the September equinox on September 22.

The third full moon – our seasonal blue moon – will be on August 22. All full moons are opposite the sun as seen from Earth rising fully illuminated at local time at sunset and setting at sunrise.

You may be wondering if the Moon takes on a blue color. Well, blue colored moons are extremely rare and have nothing to do with the calendar or the phases of the moon; neither do they have to be full moons. When a blue colored Moon occurs, the blue color is the result of water droplets in the air, certain types of clouds, or particles thrown into the atmosphere by natural disasters, such as ash. volcanic and smoke. In addition, blue colored moons in photos are created using special blue filters for cameras or in post-processing software.

In 1883, an Indonesian volcano called Krakatoa produced such a large eruption that scientists compared it to a 100 megaton nuclear bomb. Ashes from the Krakatoa explosion rose into the atmosphere for up to 80 kilometers (50 miles). Many of these ash particles can be around 1 micron in size, which could scatter red light and act as a blue filter, causing the Moon to appear blue.

Blue-colored moons appeared for years after the 1883 eruption. Many other volcanoes throughout history, and even forest fires, are known to affect the color of the moon. Typically, to create a bluish moon, the dust or ash particles should be larger than about 0.6 microns, which scatters red light and allows blue light to pass freely. That said, what we call a Blue Moon usually appears a pale gray, white, or yellowish color just like the Moon on any other night.

Typically, blue moons occur every 2 to 3 years. Our last blue moon was on October 31, 2020 – Halloween night. March was red and very tall because it was closer to Earth, and it was seen in the sky near the Blue Moon. Coincidentally, this year’s Blue Moon will appear near the planets again, but this time Jupiter and Saturn! We won’t see another Blue Moon until August 2023.