Blue Moon Alert - Sunday May 31, 2026

Blue Moon
Spaceweather.com

BLUE MOON ALERT: Tonight's full Moon is no ordinary full Moon. It's a Blue Moon. To see it, step outside at sunset and spin round to face east. Just don't be surprised if it is orange:

This is a "calendar Blue Moon," the second full Moon within a single calendar month. May 2026 opened with a full Moon at the start of the month, and now closes with another. According to tradition, the second full Moon is "Blue."

Two full Moons squeeze into a single month once every two to three years. The phenomenon does not alter the Moon's natural colors. Low-hanging Blue Moons are typically orange (because of scattering in the atmosphere) while overhead Blue Moons are the gray shades of moonrock.

But here's the twist: Moons CAN actually turn blue. It's rare, but real.

True blue Moons require unusual atmospheric conditions caused by forest fires and volcanoes. When the air is loaded with smokey particles slightly wider than the wavelength of red light (about 1 micron across) those particles preferentially scatter red wavelengths while letting blue light pass through. The result: a Moon tinged genuinely blue.

Following the 1883 eruption of Krakatoa, observers reported blue Moons for nearly two years. The 1980 eruption of Mt. St. Helens produced them, as did the 1991 eruption of Mt. Pinatubo. Smoke from wildfires in western Canada in September 1950 turned Moons blue across North America and Europe for weeks.

This Sunday, step outside and look up. The Moon will be full, bright, and, barring a volcanic calamity or forest fire, stubbornly silver. Enjoy the "Blue" moonlight anyway!

--SpaceWeather.com is written by Dr. Tony Phillips