We were walking back to the unit after rockpooling at night when we saw this circle around the moon. Fortunately, a number of people in the Apollo Bay/Otways Facebook group had noticed the same thing and had posted information about what it was called.
It is a moon halo or 22° halo. It happens when as direct moonlight is refracted in millions of hexagonal ice crystals suspended in the atmosphere.
We dipped on the invertebrates we were looking for this trip, so it was pretty awesome to get another surprise.