A Rare Blue Moon Lights Up the Sky on May 31

May closes with a spectacular celestial double the month’s second full moon rises tonight, and skywatchers won’t get another chance like this for over two years.

Full Blue Moon rising in the night sky on May 31 2026 — rare second full moon of the mont — The full moon illuminates the night sky — May 31, 2026 marks a rare Blue Moon, the second full moon of the month. The next will coincide with New Year’s Eve in December 2028. (Photo: RIA Novosti / Sergei Kirkach)

What Is a Blue Moon And Why Does It Happen?

May 2026 is closing with a rare astronomical treat a second full moon rising on the very last day of the month. Scientists from the Solar Astronomy Laboratory at Russia’s Institute of Space Research explained the phenomenon. They noted that full moons occur roughly every 29.5 days. Because that cycle is slightly shorter than most calendar months, two full moons occasionally fall within a single month. When this happens, the second full moon earns the nickname the Blue Moon.

The term comes from the old English expression “once in a blue moon,” meaning something extraordinarily rare. The Blue Moon doesn’t actually turn blue in color it’s purely a calendrical quirk. The first full moon of May 2026 rose on May 2nd. Tonight’s Blue Moon on May 31st completes the pair a rare back-to-back appearance in one month.

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When Did This Last Happen And When’s the Next One?

“The last time this occurred was in August 2023 I personally watched that second full moon on August 31st from the Ostankino Tower. The next time it will happen is in December 2028. The Blue Moon meaning the second full moon of that month will rise on December 31st, coinciding with New Year’s Eve,” the Solar Astronomy Laboratory wrote in its official Telegram channel.

That means skywatchers have a long wait ahead. The next Blue Moon won’t appear for more than two years making tonight’s event well worth stepping outside for a look.

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A Sky Event You Shouldn’t Miss Tonight

The Blue Moon is one of those quiet, unhurried sky events no special equipment needed, just clear skies and a good view of the horizon. Since full moons rise around sunset, tonight is the perfect opportunity for an evening stroll under a brilliantly lit sky. Scientists also remind that while the Blue Moon is a special calendar event, the Moon itself appears identical to any other full moon just as bright, just as beautiful, and arguably more meaningful when you know how rarely it comes around.