This week is a special week for lunar sightings thanks to a ‘once in a blue moon’ event.
A ‘blue moon’ doesn’t refer to the moon’s colour, but the number of times it can be seen. On Sunday 31 May, there will be a full moon – the second in the month of May – known as a blue moon. Usually, in each calendar month, there is only one full moon, but May is an exception to this rule.
Coincidentally, this will also be a ‘micromoon’, as the moon will appear smaller than usual thanks to it being further away in its orbit from the earth.
According to the Royal Observatory, we are due another blue moon on 20 May next year. The last time there was a blue moon was August 2023, according to AccuWeather.
It’s been a very auspicious time for stargazing and celestial events lately – earlier this month saw the annual Lyrid meteor shower litter the skies.
What is a ‘blue moon’?
‘Blue moon’ was originally the term for the third full moon of a season containing four moons. Now it’s also given to a second full moon in a single calendar month.
Why is there a ‘blue moon’?
What makes a blue moon rare is that they only occur every two to three years.
Because the phases of the moon take 29.5 days to complete, it takes 354 days to complete the full 12 cycles. But since there are 365 days in a year, this means that approximately every two and a half years a 13th full moon is spotted.
According to the Royal Observatory, the last full Moon was at 6.23pm on 1 May 2026. The next full Moon is on 31 May at 9.45am in the UK. As this is the second full moon in a month, it’s known as a ‘blue moon‘.
What causes the phases of the moon?
The phases of the moon are determined by where the moon, sun and earth are positioned.
Since the moon doesn’t produce light on its own, we can only see parts of it when it is light up by other objects. Distant stars emit a small amount of light and earthshine, the reflection of light from the earth, can all help showcase some of it, but it’s the sun that provides the moon’s main source of light.
Do you need any equipment to see it?
No – the blue moon should be visible without telescopes or special equipment depending on the weather conditions. Those further away from city lights with access to a clear sky will have the best chance of seeing it.
