What is the significance of a blue moon?

The significance of a blue moon lies in its definition as a rare occurrence of two full moons happening within a single calendar month. This phenomenon typically happens because the lunar cycle, which lasts about 29.5 days, occasionally allows for this alignment when there are two full moons in a month that already has 31 days. This concept of a blue moon contributes to its popularity in culture and idiomatic expressions, where it symbolizes rarity.

While the other options reference various characteristics about moons, they do not accurately describe the blue moon phenomenon, thus highlighting the uniqueness of having two full moons in a single month as the true hallmark of a blue moon. Understanding this helps clarify the common misconceptions related to lunar events and emphasizes the cultural significance attributed to lunar cycles.