'Blue moon' appears for a second time in 2018

The blue moon rises behind Lisbon's Saint George Castle as night falls on Saturday, March 31, 2018. [Photo: IC]View of the Blue Moon from the village of Sant Elm on in Majorca Island, in eastern Spain, on Saturday, March 31, 2018. A 'blue moon' appeared for the second time this year on Saturday, March 31, 2018. A blue moon is means a second full moon within one a calendar month, which is quite rare. The next blue moon is due in October 2020. [Photo: IC]