What makes the harvest moon so special? Mainly it's the path it's following this week. The moon always travels close to the ecliptic, the path of the sun and planets in the sky, but this week the ecliptic is at a particularly shallow angle to the horizon. The result is that the moon never gets too far above the horizon all night long for a number of nights in a row, putting it literally “in your face.” There is a well known but poorly understood optical illusion known as the “moon illusion,” whereby the moon, when low in the sky, appears much larger than it does when high overhead. This really is an illusion, as you can see for yourself by blocking the moon with a finger held at arm's length: the moon is no bigger on the horizon than overhead. When the moon is low in the sky, it is also strongly subject to appearing yellow, orange, or red due to air pollution, particularly caused by forest fires this time of year.