Once in a Blue Moon

If you’re looking for something to happen “once in a blue moon,” look for it this Friday. This actually not so rare event occurs when two full moons appear during one calendar month. Because the previous full moon occurred on August 1^st, the full moon appearing on August 31^st is called a “blue” moon. And while that is how we define a blue moon now, originally a blue moon occurred when there were four full moons during a single season. Does the moon actually appear blue? Well, no. As long ago as the 16th century, the expression “the moon is blue” meant something that was impossible. However, the moon can appear greenish or bluish just before sunrise or just after sunset, if there is enough dust in the atmosphere.

To learn more fun facts about the moon, check out the Los Altos Library’s outstanding science collection. This part of our collection is funded in large part by the Los Altos Library Endowment.

The Book of the Moon

Moon

Return to the Moon