The appearance of a blue sun is triggered by volcanic dust, smoke from forest fires, desert dust, smog and other forms of pollution. Wavelengths of visible light that are blue in color become scattered from the rays of the sun reflected off of smog, smoke, or ash particles. The phenomena are extremely rare because the particles suspended in the air scatter blue wavelengths only when they are of a particular size. Smoke, volcanic ash and smog often provide clouds that are gray in color, setting the perfect backdrop for blue light to scatter off the particles composing the cloud. The size of these particles must be less than 0.85 micrometers, which is very tiny (0.03 thousandths of an inch!). The sun can take on a greener hue when the particles are larger than 1.1 micrometers. Reports of a blue sun have occurred in Egypt in December 2006, as a result of smoke from farmers burning brush. According to the AccuWeather.com Almanac, that notes historical weather events, the southern U.S. observed a blue sun that continued for several days in August of 1831 centered on August 13. This event likely happened as a result of local forest fires in Virginia, but the August 13 blue sun is said to have been "a signal" taken by Nat Turner to begin his rebellion in Southampton County, Virginia. Nathanial “Nat” Turner was an enslaved man who led the rebellion of enslaved people on August 21, 1831. His action set off a massacre of up to 200 black people and a new wave of oppressive legislation prohibiting the education, movement, and assembly of enslaved people. The rebellion also stiffened proslavery, anti-abolitionist convictions that persisted in that region until the American Civil War. The blue sun that prompted the rebellion, hardened positions and helped hasten the conflict between slaver holder and abolitionists that brought about the Civil War and ultimately emancipation. Reports of a blue sun came from Egypt in 2006, as a result of smoke from farmers burning brush. In 1978, dust storms in Mongolia are said to have caused a blue sun to be visible in Beijing, China.
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