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A rare celestial event is set to dazzle skywatchers across the United States in the early hours of Sunday, (May 31), as a blue micromoon reaches its peak fullness. This phenomenon occurs when two full moons fall within the same calendar month, with the second one, called a blue moon, coinciding with the moon's apogee, the farthest point from Earth in its orbit.
The last time a monthly blue moon graced the sky was several years ago, and the next won't appear until December 31, 2028. The "micromoon" title means this full moon will appear about six percent smaller and over ten percent dimmer than average.
The best viewing opportunity will be during moonrise late on Saturday, (May 30), shortly after sunset. Stargazers should look for an open eastern horizon as dusk settles in. While the event is called a blue moon, the moon itself will likely glow golden-orange near the horizon due to Rayleigh scattering, the same effect that makes sunsets red and orange. No special equipment is needed, though binoculars can enhance the view of the moon's surface.
This month's lunar show follows the Flower Moon, which peaked on Friday, (May 1), making this second full moon a rare sight in May. As noted by The Old Farmer’s Almanac, the moon will be at its fullest at 4:45 a.m. EDT on Sunday, (May 31). The micromoon occurs just before the moon reaches apogee on Monday, (June 1).