In 1883, though, people saw blue moons, green moons, lavender suns and even noctilucent clouds that glowed at night. Sounds impossible, right? The reason was Krakatoa, an Indonesian volcano that spewed ash to the top of Earth’s atmosphere. The explosion was equivalent to a 100 megaton nuclear bomb and the atmospheric affects lasted for years. The ash plumes were filled with particles 1 micron wide, about the same wavelength as red light. The particle scattered the red light, allowing the blue to pass through, thus acting like a blue filter.