NASA and astronomers have confirmed a rare Blue Moon will occur on May 31, 2026 [1].
This event is significant because it combines two rare lunar occurrences: a calendar Blue Moon and a micromoon. The alignment provides a unique opportunity for global observation of the lunar cycle at its furthest point from Earth.
NASA said the full moon on May 31 qualifies as a Blue Moon because it is the second full moon to fall within a single calendar month [1]. While the term "Blue Moon" is common, it does not refer to the actual color of the moon. Instead, it describes the timing of the lunar phase within the Gregorian calendar.
In addition to being a Blue Moon, this event will be the smallest full moon of 2026 [3]. Astronomers refer to this as a micromoon, which happens when the moon is near its lunar apogee, the point in its orbit farthest from Earth [5]. Because of this distance, the moon will appear slightly smaller than average [3].
The event will be visible worldwide, including to observers in locations such as Oregon, U.S. [1, 4]. The timing of the micromoon also coincides with the Eta Aquariids meteor shower [5]. This meteor shower originates from debris left by Halley's Comet [5].
Skywatchers can expect to see the moon reach its full phase at the end of May [1, 2]. While some reports suggest the event will dazzle observers, the physical size of the moon will be at its minimum for the year [3].
“"The full moon on May 31 qualifies as a Blue Moon because it is the second full moon to fall within a single calendar month."”
The occurrence of a micromoon during a Blue Moon phase highlights the eccentricity of the lunar orbit. Because the moon's path is elliptical rather than circular, its distance from Earth varies, affecting its perceived size. The overlap with the Eta Aquariids meteor shower adds a secondary astronomical layer to the event, though the brightness of a full moon typically makes observing meteors more difficult.
