In a recent Instagram video, shared by The Museum of Science breaks down why the upcoming blue moon is rare and why the moon will not actually turn blue.May 2026 Blue moon (Pinterest)“Once in a blue moon” is usually just a saying people use for something that rarely happens. But on May 31, the phrase will match a real event in the night sky.A rare blue moon is expected to appear, catching the attention of skywatchers, moon lovers, and astrology followers. If you are imagining a glowing blue moon hanging in the sky, there is one thing to know first. That is not what a blue moon means.What is a blue moon?A blue moon has nothing to do with the moon’s colour.According to the Museum of Science, a blue moon happens when two full moons fall within the same calendar month. Since the moon’s cycle lasts about 29 and a half days, most months only have one full moon. Every few years, however, the timing works out differently, and a second full moon slips into the same month.That uncommon timing is what gives the event its name.Also Read May 2026 ends with two Full Moons, and the second one brings a powerful shift to zodiac signs, as per an astrologerWill the moon actually look blue?Not this time.The Museum of Science explains that the May 31 event is a calendar phenomenon, not a colour change in the sky.The moon can occasionally appear bluish because of smoke, dust, or unusual atmospheric conditions, but that is a separate phenomenon.Why are people talking about the May 31 blue moon?Part of the excitement comes from how uncommon these events are. A second full moon in the same month does not happen every year. According to the Museum of Science reel, blue moons show up only every couple of years.For skywatchers, that makes it a good excuse to step outside and spend a few minutes under the night sky.For astrology followers, rare full moons often carry symbolic meaning. Some people connect them with reflection, emotional awareness, or taking stock of where life is heading.Also Read Full Moon May 2026: An expert shares powerful rituals to release negative energy during this rare Blue MoonWhether you follow lunar events for science, symbolism, or simple curiosity, the May 31 blue moon is one of those moments that invites people to look up and pay attention. After all, “once in a blue moon” does not come around very often.Disclaimer: This article is based on user-generated content from social media. Reader's discretion is advised.