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The second full moon of May shines at 5:44 AM (Brasília time), appears visually smaller than normal, and rises next to the red star of Scorpio. See the step-by-step guide to observe it with the naked eye, anywhere in the country.
Those who look to the sky on the dawn of May 31st will witness an astronomical arrangement that only repeats every few years. The so-called Blue Moon, the second full moon within the same calendar month, reaches its peak illumination at 5:44 AM Brasília time, will also be the most distant micromoon of 2026, and will visually rise next to Antares, the giant red star of the constellation Scorpio. No telescope or trip to the countryside is needed. In any city in Brazil, a clear sky and an open horizon are enough to observe the phenomenon.
And there’s a detail that completely changes how this moon is seen.
The Blue Moon doesn’t turn blue. So why is it called that?
The answer is older than it seems.
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The expression comes from the English “once in a blue moon,” used since the 16th century to describe something improbable. Back then, saying the moon was blue meant saying something would never happen. Over time, the meaning changed: the phrase came to designate something rare, but possible.
In modern astronomy, the term gained a mathematical definition. A Blue Moon is the second full moon that occurs within the same calendar month. Since the lunar cycle lasts about 29.5 days and months have between 28 and 31 days, it is possible for two full moons to fit into a single month. But the coincidence is not trivial.
According to the science communication portal EarthSky, cited in a CNN Brazil report, this configuration occurs only seven times every 19 years. Hence the survival of the expression “once in a Blue Moon” as a synonym for a rare event.
And there’s a curious effect behind this. The phenomenon is connected to the so-called Metonic cycle, an astronomical relationship in which 235 lunar months are approximately equivalent to 19 solar years. This discrepancy between cycles causes a full moon to “remain” from time to time, creating the said Blue Moon.
In 2026, this encounter happens on May 31st. And it doesn’t come alone.
Why this full moon will be different from all others this year
Here’s what sets this event apart from the rest.
The Blue Moon of May 31st coincides with the furthest point of the lunar orbit in relation to Earth. This point is called apogee. When the full phase occurs near the apogee, the satellite appears slightly smaller and less bright than normal. It’s the opposite of the famous supermoon. Astronomers call the phenomenon a micromoon.
Estimates reproduced in specialized publications indicate that this moon may appear between 12% and 14% smaller than a traditional supermoon. To the naked eye, the difference is subtle. In a comparative photograph, it is evident.
And there’s another element entering the scene.
On the same night, the Moon will be visually close to Antares, one of the most well-known stars in the night sky. Antares is a red supergiant, classified among the largest stars observable with the naked eye, and shines with an unmistakably orange hue. The contrast between the silvery-white of the full Moon and the red of Antares creates a visual effect that often yields good images, even with cell phone cameras.
In other words: three phenomena in a single night. Blue Moon, micromoon, and apparent proximity to Antares. For those who have never observed the sky carefully, the combination serves as an ideal entry point.
When, where, and how to observe (step by step)
Now for the practical part.
The peak illumination occurs at 5:44 AM on May 31, Brasília time. This corresponds to 8:45 AM Coordinated Universal Time (UTC). At this exact moment, in part of Brazil, the Moon will already be close to setting on the western horizon, near dawn.
Therefore, the observation window starts earlier.
The full moon looks practically the same to the human eye around 24 hours before and 24 hours after its peak. This means observation is good from the evening of the 30th until the morning of June 1st. For those living in São Paulo and a good part of the Southeast, the evening of the 31st offers another opportunity: the Moon rises in the east around 5:30 PM, still low on the horizon, and gains that larger apparent size due to an optical effect, a phenomenon known as the lunar illusion.
To make the most of the observation:
- Look for a place with an open horizon and little artificial lighting. Rural areas, mountainous regions, and viewpoints offer the best visibility.
- Wait for your eyes to adapt to the dark for about 15 to 20 minutes before drawing conclusions about the brightness of the sky.
- Neither a telescope nor binoculars are necessary. But using common binoculars helps to perceive craters and reliefs on the lunar surface.
- On cell phone cameras, activating night mode and HDR balances the Moon’s light with the surrounding sky, preventing blown-out highlights.
- To photograph the microluna next to Antares, it’s best to wait for the Moon to rise a little above the horizon and use optical zoom, not digital.
And there’s a detail that few outlets have mentioned in the articles published so far.
The Moon has actually turned blue. And the reason is grim
Although the name is just a convention, the Moon has appeared with a literally bluish hue in historical records. And it wasn’t because of the astronomical phenomenon that shares the same name.
The most famous case occurred in 1883.
That year, the Krakatoa volcano in Indonesia erupted in one of the largest explosions recorded by modern science. The column of ash and smoke released into the atmosphere spread fine particles worldwide. In several countries, observers reported seeing sunsets with strange colors and the Moon with a bluish hue for months.
The explanation lies in the size of the particles. According to EarthSky, the Moon can acquire a bluish appearance when the atmosphere carries particles with a diameter slightly larger than 900 nanometers. This type of particle filters red light and preferentially allows blue light to pass through, reversing the common effect seen in sunsets and moonrises.
Similar cases were recorded after large forest fires in Canada in 1950 and after the eruption of the El Chichón volcano in Mexico in 1982.
In other words, a true Blue Moon exists. But it requires atmospheric circumstances that no one desires.
May’s sky already delivered another spectacle (and most missed it)
Before the Blue Moon closed the month, May started busy for astronomy enthusiasts.
Between the night of May 5th and the dawn of May 6th, Brazil experienced the peak of the Eta Aquariids meteor shower, considered one of the most active observable from the Southern Hemisphere. The phenomenon is formed by fragments left by Halley’s Comet, which cross the Earth’s atmosphere at high speed and form the luminous trails popularly known as shooting stars.
Under ideal conditions, the shower can produce between 40 and 50 meteors per hour.
CNN Brazil interviewed three specialists about the event. Astronomer Marcelo Rubinho evaluated the forecast as “a good forecast, a great event.” Emerson Perez, from Urânia Planetário, indicated the best observation time as the interval between 3:30 AM and 4:00 AM, with the gaze directed between the east and north of the sky. Professor Thiago S. Gonçalves, from the Federal University of Rio de Janeiro (UFRJ), highlighted that the proximity to the full moon on May 1st ended up hindering the observation of weaker meteors.
In other words: those who live far from urban lights and woke up early saw a piece of a comet crossing the sky. Those who missed it still have the Blue Moon as a second chance in the same month.
When will the next Blue Moon be
For those who miss the May 31st observation, there’s good news. Due to a rare combination, 2026 features two monthly Blue Moons.
The first is in May. The second is scheduled for October.
This duality only occurs in years where February has no full moon, a situation that makes room for extra full moons in other months of the calendar. After that, the next seasonal Blue Moon, a less discussed type defined by the presence of four full moons in a single season, is scheduled for May 20, 2027.
But it is the May 31st Blue Moon that simultaneously brings together the most unusual conditions: the second full moon of the month, the year’s most distant microluna, and visual proximity with Antares.
Lunar calendar for May 2026 (Brasília time)
- Full Moon (Flower Moon): May 1st, at 2:22 PM
- Waning Moon: May 9th, at 6:13 PM
- New Moon: May 16th, at 5:03 PM
- Waxing Moon: May 23rd, at 8:12 AM
- Full Moon (Blue Moon, microluna): May 31st, at 5:44 AM
Print it, note it on your phone, save it wherever you prefer. In just over two weeks, the sky will present the rarest phenomenon of the year so far.
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