The discussion centers around the phenomenon of seeing unusually large moons, often described as "giant moons." Participants share personal experiences of witnessing these impressive sights, particularly when the moon is low on the horizon, which can create an optical illusion known as the Ponzo effect. This effect makes the moon appear larger when compared to foreground objects. However, some contributors argue that certain atmospheric conditions can create a more pronounced visual effect, making the moon seem significantly larger than usual, even without nearby reference points. The conversation also touches on the moon's elliptical orbit, which brings it closer to Earth during certain times, such as during full moons at perigee. While many agree that the moon's perceived size is primarily an illusion, there are claims of experiencing a truly massive moon that defies typical explanations, suggesting a rare atmospheric phenomenon. Overall, the thread highlights the interplay of perception, atmospheric conditions, and the natural beauty of the moon.