This Tuesday night, the moon will turn full but it will be the smallest we've seen for the year. Last Saturday, we saw a large luminous moon during the International Observe the Moon Night, and now we'll see the opposite tonight.

The moon is going to appear at a small size due to its increased distance from Earth when it is full. Because it will also be orbiting much slower, we are likely to see this small full moon for the next several days.

Regularly, full moons reoccur at roughly 29-day periods. The moon's distance from the Earth is described by its apogees and perigees. Apogees refer to the furthest point from us, while perigees are the closest point from Earth. Thus, what is happening now is a full moon overlapping with a perigee, which causes the next perigee to occur earlier by a few days. As a result, the full moon about a half a year later will be coinciding with its apogee. Essentially, this is what we will be seeing tonight.

As predicted, we will experience another perigee coinciding with the new moon around Oct. 26.