On July 31, 2015, what’s known as the Blue Moon will appear. Every month has a full moon but about every three years, due to the lunar cycle and the calendar year, we see two in the same month. The last time the Blue Moon appeared in the US was August 2012.
The Blue Moon is a bit of a misnomer. In most of the US, it won’t be blue. It’ll be pearly-gray. But in the West, forest fires produce ash and/or oily-smoke that contain the particles that could make the Blue Moon blue. For best viewing, NASA suggests stepping outside at sunset and looking east.