A rare celestial event is set to grace the night sky this weekend as a blue moon appears for the first time in nearly two years. Stargazers across the UK will have the opportunity to witness this phenomenon, weather permitting.
What is a Blue Moon?
A blue moon occurs when there are two full moons within the same calendar month. The second full moon is traditionally called a blue moon. Despite its name, the moon does not usually appear blue in colour, though there are rare exceptions when atmospheric conditions cause it to take on a different hue.
The last blue moon was observed in August 2024. This weekend's event will see the moon reach its peak illumination on Sunday, May 31, but the best viewing time is expected to be on the evening of Saturday, May 30, when the moon rises shortly after sunset and remains visible throughout the night.
Why This Blue Moon is Special
Astronomy expert Alan Jones from 365 Astronomy explains that this blue moon is also a micromoon. This means the moon is near the furthest point in its orbit from Earth, making it appear slightly smaller and dimmer than usual, although the difference is subtle. He advises choosing a location with clear views of the eastern and southern horizon, away from tall buildings and trees, for the best experience.
Why the Moon Can Appear Orange or Red
As the moon rises or sets near the horizon, it can take on orange, amber, or reddish tones. This occurs because Earth's atmosphere scatters shorter blue wavelengths of light, allowing longer red wavelengths to dominate. 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?
According to Alan Jones, full moons are excellent targets for casual observers, families, and beginner astronomers. The rarity of a blue moon, reflected in the phrase 'once in a blue moon,' captures people's imagination and encourages more of us to look up at the night sky. While not exceptionally rare astronomically, these events still hold a special appeal.
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. Smartphones can 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 excellent beginner-friendly options for capturing detailed lunar images.
When is a Blue Moon Actually Blue?
According to the Royal Museums Greenwich, blue moons are not actually blue in colour, except in two rare cases: during a lunar eclipse, the moon can turn blood red, and in very rare circumstances, the moon can appear blue when viewed through a haze of dust particles in the atmosphere, perhaps from a recent volcanic eruption. From space, however, the moon always looks grey.
