People all over the world will be able to see a blue micromoon in the night sky this weekend––a rare celestial event that isn’t expected to happen again for more than 25 years. 

During the event, the moon will be the smallest-appearing and farthest away from Earth of any full moon this year. 

Here’s what to know about the micromoon, and how to see it best.

What is a blue micromoon?

A blue moon refers to the second full moon in a single month, which is a fairly uncommon occurrence in and of itself, happening only roughly every two to three years. The last blue moon was on August 31, 2023, and the next one will come on December 31, 2028, according to EarthSky. 

A blue moon is not actually blue in color; the name simply refers to the rarity of the phenomenon. Before first being applied to the second full moon in a month—mistakenly—in a 1946 issue of Sky and Telescope magazine, the term used to refer to the third of four full moons in a single season. 

A micromoon, meanwhile, is a full or new moon at the farthest distance in the moon’s orbit from Earth, a point called apogee. 

Saturday night’s blue micromoon is a combination of the two phenomena: it will be the second full moon of May, and it will also reach apogee, making it appear roughly 10% dimmer and 6% smaller than an average full moon, according to Gianluca Masi of the Virtual Telescope Project, who spoke to The Associated Press. 

The moon will be this year’s smallest-looking moon, at approximately 252,360 miles (406,134 km) away from Earth. The average distance of the moon from the Earth is around 238,900 miles (384,472 km). 

The opposite of a micromoon is a supermoon, which occurs when a full moon reaches perigee, or its closest point to Earth on the moon’s orbit. During the last supermoon—of which the past year has seen several—the moon was roughly 225,130 miles away (362,311 km). 

The moon’s distance from Earth varies due to the elliptical trajectory of its orbit, which also changes how big it appears in the sky, though relatively imperceptibly. 

A moon being at perigee makes only a marginal difference in one’s perception of its size, despite the fact that it is closer to the Earth. What makes the moon appear quite large sometimes is effectively an illusion based on its position relative to the horizon. When situated against a backdrop––say, mountains, buildings, trees––the moon can appear to be inflated compared to those smaller objects that take up less room in one’s view.  

The first full moon of this month––the flower moon, so dubbed for the season it occurs in––was on May 1. 

When can you see it?

The blue micromoon will be visible the night of Saturday, May 30, into Sunday, May 31.

It will peak at 4:45 a.m. EDT on Sunday. 

How can you see it best?

Like many solar events, the blue micromoon is best seen with an unobstructed view, clear skies, and away from bright lights. However, the small differences in the moon’s brightness and size won’t be obvious to the naked eye. 

For those in the Northern Hemisphere, the moon will be closely situated near Antares, a bright star at the heart of the constellation Scorpius, which resembles a scorpion in the sky.

South of the equator and across the Pacific, some will see the moon cross over the constellation and obstruct the view of Antares temporarily.