Overview
- The month began with a full moon on May 1 and will end with a second full moon on May 31, 2026, making May a blue moon month under the modern definition.
- The modern use of 'blue moon' means the second full moon in a single calendar month and became widely used after a 1946 misreading of an almanac.
- Both May full moons occur near lunar apogee so they will be micromoons that look about 6–7% smaller and roughly 10% dimmer than typical full moons.
- The term does not mean the Moon will actually be blue for most viewers because ordinary atmospheric conditions do not change its color.
- Large volcanic eruptions can make the Moon appear blue by lofting 1‑micron aerosols into the stratosphere, a phenomenon documented after Krakatoa in 1883, and skywatchers and photographers are advised to watch from dark, open areas for the best views.