Blue moon: Why the moon won't actually be blue tonight

The clever people at Nasa explain why the blue moon isn't really going to be that blue

Kiran Moodley
Friday 31 July 2015 10:43
What is a blue moon?

July 2015 will see two full moons: the first occurred on July 2 and the second will take place on July 31.

This evening's "blue moon" will be the first one since 2012 — and the last until 2018 — is set to be seen in the sky.

However, that does not mean the Earth’s moon will appear blue to anyone that sees the full moon tonight. The history of how the second full moon in a calendar month came to be known as a “blue moon” is rather complex in itself.

Fortunately, Nasa has provided a simple explanation to the terminology in a short video – as well as explaining what it would take for the moon to actually appear blue, rather than its usual hue of pale grey and white.

Blue moons are due to the difference between calendar and lunar months. While a calendar month lasts from 28 to 31 days, a lunar month - the time interval between two full moons - is always 29.53 days long.

Register for free to continue reading

Registration is a free and easy way to support our truly independent journalism

By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists

Already have an account? sign in

By clicking ‘Register’ you confirm that your data has been entered correctly and you have read and agree to our Terms of use, Cookie policy and Privacy notice.

This site is protected by reCAPTCHA and the Google Privacy policy and Terms of service apply.

Join our new commenting forum

Join thought-provoking conversations, follow other Independent readers and see their replies


Thank you for registering

Please refresh the page or navigate to another page on the site to be automatically logged inPlease refresh your browser to be logged in