The Harvest Moon isn’t always in October, and this is one of those years.
A Harvest Moon is defined as the full moon closest to the autumnal equinox. This is the full moon of October about 75% of the time. This year’s autumnal equinox occurs on September 22. That means that the full moon on September 8 is a few days closer than the full moon of October 8. So in 2014 the full moon names flip, with the Harvest Moon in September and the Hunter’s Moon in October.
As to the “Supermoon”–this term began with astrologer Roger Nolle in 1979; it’s not an astronomical term. Since the moon’s orbit is an ellipse, its distance from the earth varies. Its furthest point is called “apogee”, and it’s farthest point is called “perigee”. Consequently, a full moon at perigee is up to 14% larger and 30% brighter than one at its farthest point.
Even though “supermoon” isn’t technically correct astronomically, at least the media coverage has gotten people to go out and look at the night sky, and that’s a good thing!