As the famous phrase says : “Once in a Blue Moon” – so what is this Blue Moon. Blue Moon is a phenomenon as explained by science –
Full moons occur every 29.5 days on average, when the moon is directly opposite the sun from the perspective of Earth. This causes its whole disk to be fully illuminated as a large, bright circle. Usually, when the moon is full, it passes either above or below Earth’s shadow, but sometimes, when it is perfectly aligned, it travels right through the shadow, causing a lunar eclipse, when its disk is dark.
Blue Moons don’t happen too often, which is why the phrase “once in a Blue Moon,” has sprung up to mean only very rarely. After Tuesday’s event, the next Blue Moon isn’t set to occur until 2015.