Have you ever looked up at the night sky and seen a blue moon? A blue moon doesn't happen at1fixed time and it is not a common sight. And most of the time, it isn't actually blue. A blue moon takes place when there2two full moons in one month. Most months have 30331 days, so sometimes a month will have two full moons.
In fact, the moon doesn't change the color to make4appear orange, red or blue. Instead, particles (微粒) in the Earth's atmosphere (大气层) lead to the result. For example, the moon5appeared blue in Indonesia in 1883. That year, the volcano Krakatoa erupted (爆发). The ash (灰)6into the air, which stayed in the atmosphere for quite a while. It had the effect of making the moon appear blue.
In 2020, sky-watchers were in for a treat when a blue moon lighted up the night sky7October 31, the first time that had happened in nearly 20 years.
The blue moon also has another8. Have you ever heard the phrase "once in a blue moon"? When people say that, they mean9something uncommon happens—like a blue moon.
What other colors have you seen the moon takes on? Carry on watching the night sky and you are sure10a beautiful moon at some point.
