Stargazers who cast their eyes skyward this weekend could be treated to a remarkable sight with an unusual lunar phenomenon which last occurred nearly two years ago. May 2026 will witness two full moons appearing within the same calendar month.

The second full moon, referred to as a blue moon, will appear on Saturday night, offering stargazers an additional opportunity to witness one of the year's most spectacular displays. And while it usually isn't blue but rather appears the same colour as an ordinary moon, there are occasions when it does alter its hue.

The occurrence is uncommon as most months will feature just one full moon, with the previous blue moon taking place in August 2024. Astronomy specialist Alan Jones from 365 Astronomy clarifies why this blue moon is noteworthy, when to observe it in the UK, and how to secure the best way of seeing it, reports Wales Online.

When to see May's blue moon

Alan explained: "The blue moon reaches peak illumination on Sunday, the 31st, although the best time for stargazers will be on the evening of Saturday, May 30th, when the moon rises shortly after sunset and stays visible throughout the night. It will sit relatively low in the southern sky, so choosing a location with clear views of the eastern and southern horizon, away from tall buildings and trees, will provide the best experience."

Why this blue moon is special

"A blue moon is the second full moon within a single calendar month, something that happens only every two to three years. Despite the name, the moon will not actually appear blue, " said the expert. "This year's event is also a micromoon, meaning the moon is near the furthest point in its orbit from Earth. It may appear slightly smaller and dimmer than usual, although the difference is subtle."

Why the moon can appear orange or red

Alan said: "As the moon rises or sets near the horizon, it can take on orange, amber or reddish tones because Earth's atmosphere scatters shorter blue wavelengths of light. The well-known 'moon illusion' can also make the moon appear larger when it is low in the sky, even though its actual size does not change."

Is the blue moon worth observing?

"Full moons are excellent targets for casual observers, families and beginner astronomers," said Alan. "A blue moon also carries a sense of rarity reflected in the phrase 'once in a blue moon'. While not exceptionally rare astronomically, these events still capture people's imagination and encourage more of us to look up at the night sky."

Tips for viewing and photographing the moon

"Binoculars are a great way to enhance the view, revealing darker maria and brighter crater regions on the lunar surface," said the expert. "Smartphones can also capture impressive images when mounted on a tripod and used with manual exposure settings.

"For dramatic moonrise photos, include buildings, trees or landscape features in the foreground to help show the moon's scale against the horizon. For closer lunar photography, a telescope with an aperture of around 80mm or more will provide crisp detail. Smart telescopes such as the Dwarf 3, Seestar S30 or S50, eVscope 2 and Vespera II are also excellent beginner-friendly options for capturing detailed lunar images."

When is a blue moon actually blue?

According to the Royal Museums Greenwich, there are occasions when a blue moon genuinely does appear blue. It said: "Blue moons aren't blue! Blue moons remain the same colour as any other full moon except in two rare cases:

• During a lunar eclipse, the moon can turn blood red, lit only by the light bent around the Earth by its atmosphere onto the face of the moon. As lunar eclipses occur only during full moons, and blue moons are one type of full moon, it's very rare that a blue moon will be red!
• In very rare circumstances, the moon can appear blue, but in this case the colour would be caused by viewing the moon through a haze of dust particles in our atmosphere, perhaps from a recent volcanic eruption. From space, however, the moon will look just as grey as it always has!: