Moon Illusion

The Moon appears to be larger when viewed nearer the horizon than when higher up. By rights, it should be smaller when on the horizon - which indeed it is, if you were to measure it with scientific instruments. The Moon will be further away from you than when it is high in the sky.

Some sources state that the illusion is caused by comparison with nearby buildings. In which case you would expect the illusion to be absent if you viewed the Moon over the ocean.