'Once in a Blue Moon' is of course the saying that means something happens rarely, but it's a Blue Moon on Friday!
It's very rare to see a moon that actually looks blue in the night sky (so Roley is lucky!) Atmospheric conditions could though make this happen. Ash from volcanoes or dust particles from large forest fires, water droplets or ice crystals sometimes give the moon a bluey grey appearance like a colour filter.
Friday's blue moon is termed as such because it is the second full moon in a month. There was one at the beginning of August as well. The next Blue Moon will not be for another year - 21st August 2013. But 2018 will be a very special year for blue moons as there will be two that year. In the meantime make the most of this Friday's Blue Moon.
And if you would like to see if Roley ever found the moon visit http://www.amazon.co.uk/beautifully-illustrated-childrens-picture-ebook/dp/B007KJDHOA/ref=sr_1_1?ie=UTF8&qid=1346233723&sr=8-1
Happy sky watching!