The moon will appear roughly 12 percent smaller and 25 percent less bright
Blue Moon occurs when two full moons happen in one month—a rare event happening roughly every three years, though it won't appear blue. May's Blue Moon is also a micromoon at apogee (farthest point from Earth), making it 12% smaller and 25% less bright than a supermoon.
- Blue Moon reaches fullness May 31 at 5:45 AM, 406,135 km from Earth
- Will be 12% smaller and 25% less bright than a supermoon
- Blue Moon occurs roughly every three years when two full moons fall in one month
- Modern definition of Blue Moon originated from a 1946 typographical error in Sky and Telescope magazine
- Antares (Scorpion's Heart) visible Saturday night, closest approach during moonset early May 31
Brazil will witness rare celestial phenomena this weekend including a Blue Moon (second full moon of May), a micromoon, and alignment with Antares star. The Blue Moon, despite its name, won't actually appear blue.
The final weekend of May will bring three rare celestial events to Brazilian skies, though the most famous of them carries a name rooted entirely in misunderstanding. A Blue Moon—the second full moon to occur within a single calendar month—will reach its fullest phase on Sunday, May 31st at 5:45 in the morning. Despite its poetic name, it will not be blue. The phenomenon happens roughly once every three years, a quirk of lunar timing: full moons arrive approximately 29.5 days apart, so when the first one falls on the first or second day of a month, a second one inevitably follows before the month ends.
What makes this particular Blue Moon unusual is that it will also be a micromoon—the moon at its farthest point from Earth in its elliptical orbit, a position astronomers call apogee. At 406,135 kilometers away, it will be the smallest and dimmest full moon of 2026. Dr. Gabriel Hickel, an astronomer and professor at the Federal University of Itajubá, explains the visual consequence: the moon will appear roughly 12 percent smaller and 25 percent less bright than a supermoon, though most observers will struggle to notice the difference with their naked eye. The contrast exists mathematically more than perceptually.
The naming of the Blue Moon itself is a story of cultural accident and literary whimsy. The term originated in 19th-century British literature as a poetic way to describe lunar observation, eventually imported to the United States. Early observers believed the moon could take on a bluish tint due to volcanic particles suspended in the upper atmosphere. The modern definition—a second full moon within a calendar month—came about almost by accident in 1946, when the American magazine Sky and Telescope published an article that, due to a typographical error, associated the term with this specific lunar occurrence. The definition stuck. By the 1980s, the phrase had become popular across the United States and, through cultural influence, spread globally. The moon only appears genuinely blue under extreme atmospheric conditions: after massive volcanic eruptions or large-scale wildfires that inject particles into the air capable of filtering red light more effectively than other wavelengths.
Alongside the Blue Moon, observers will witness the Scorpion's Heart—the red star Antares positioned near the moon in the night sky. Antares can be seen Saturday night, May 30th, beginning about an hour after sunset. The closest approach between the moon and the star will occur as the moon sets in the early morning hours of May 31st. The region around Antares also contains a broad swath of the Milky Way, visible to those observing from locations free of light pollution.
The optimal viewing window requires some planning. While the Blue Moon technically reaches fullness on May 31st, the best time to prepare for observation is during moonrise on May 30th. All full moons rise as the sun sets and remain visible throughout the night, setting the following morning as the sun rises. Dr. Hickel notes that the moments of moonrise and moonset offer what astronomers call the "lunar illusion"—an optical effect that makes the brain interpret the moon as larger than it actually is. These same moments, however, provide the best conditions for photography, particularly when the moon is framed against the landscape. The weekend offers a rare convergence of celestial geometry and human perception, a reminder that what we see in the sky depends as much on where we stand and when we look as on what is actually there.
Notable Quotes
We will have the farthest full moon of 2026, at 406,135 kilometers from Earth. It will be the smallest and least bright full moon of the year, though people will scarcely notice the difference visually.— Dr. Gabriel Hickel, astronomer and professor at the Federal University of Itajubá
The moments of moonrise and moonset create a lunar illusion that makes the brain interpret the moon as larger than it is, and these are also the best moments for photographs in composition with the landscape.— Dr. Gabriel Hickel
The Hearth Conversation Another angle on the story
Why does a Blue Moon have such a misleading name if it never actually turns blue?
It's almost entirely accident. The term came from 19th-century British poetry as a romantic way to describe the moon, but the modern definition—a second full moon in one month—was pinned to it by a typographical error in a 1946 magazine. The name stuck globally by the 1980s, even though it has nothing to do with color.
So when would the moon actually appear blue?
Only under extreme atmospheric conditions. After massive volcanic eruptions or enormous wildfires, particles in the upper atmosphere can filter red light more effectively than other colors, giving the moon a genuine bluish tint. It's rare enough that most people never see it.
This particular Blue Moon is also a micromoon. What's the practical difference for someone looking up?
Honestly, most people won't notice. It'll be about 12 percent smaller and 25 percent less bright than a supermoon, but the human eye isn't sensitive enough to catch that easily. The real difference is mathematical—it's the farthest full moon of the entire year.
When should someone actually go outside to see these events?
Saturday night after sunset for Antares, the red star. But the real show is Sunday morning around moonrise on May 30th, when the moon and Antares are closest. The moon will set in the early morning hours of May 31st, and that's when you get the best view and the best photographs.
Why does the moon look bigger at moonrise and moonset?
It's called the lunar illusion—your brain interprets the moon as larger when it's near the horizon, probably because you're unconsciously comparing it to landscape features. It's not real, but it's consistent, and it actually makes for better photographs because you can frame the moon against trees or buildings.
How often does a Blue Moon actually happen?
Roughly every three years, but only when the first full moon of a month falls on the first or second day. Since full moons are about 29.5 days apart, that timing creates the second one before the month ends. It's not as rare as people think, but it's rare enough to be worth watching for.