The first Full Moon is on July 1, 2015 and goes by various names depending on what tradition you look up. There will be another post with some of the names for this full Moon in it.
The second full Moon is on July 31, 2015 and is known as a Blue Moon. Whenever there are two full Moons in the same month, the second is always called the Blue Moon. This usually happens once a year.
This is why the ancient Celtics, Native Americans, Mayans, ancient Egyptians and other older culture yearly calendar had thirteen months. The first and last day of the month was on a full Moon. These months were approximately twenty-nine days long. There was not anything like leap year because it was not needed. Many Pagan traditions still honor the thirteen-month year when celebrating Esbats and Sabbats. I personally follow a thirteen-month calendar for Esbats as I have incorporated many Celtic traditions in my Craft and spirituality.