; In the fall, throughout the Northern Hemisphere, "it will be extremely obvious to the ordinary person. The cloud of dust and gases from Mt. Pinatubo 's eruption last month , over twice the size of Mexico 's El Chichon in 1982 , rose into the stratosphere and covers 50 % of the globe . Sulfur contained in the plume becomes sulfuric acid and etches airliner windows . The plume may remain aloft for many years and is tracked by satellite . Suns appear green and moons blue in tropical summer , and in northern autumn the horizon will glow purple at sunrise and sunset . In the past 80 years , three events may have had global climatic impact -- El Chichon , observed in Bali in 1963 , and Pinatubo .
The cloud of dust and gases from Mt. Pinatubo 's eruption last month , over twice the size of Mexico 's El Chichon in 1982 , rose into the stratosphere and covers 50 % of the globe . Sulfur contained in the plume becomes sulfuric acid and etches airliner windows . The plume may remain aloft for many years and is tracked by satellite . Suns appear green and moons blue in tropical summer , and in northern autumn the horizon will glow purple at sunrise and sunset . In the past 80 years , three events may have had global climatic impact -- El Chichon , observed in Bali in 1963 , and Pinatubo .