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TIL Hydrogen-alpha solar telescopes work thanks to an optical device called an etalon, made up of two semi-reflective, optically flat plates. The flatness of the plates and how parallel they are defines the quality of the view of the Sun, which has an ‘orange peel’ appearance through the telescope

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4XRgJ TIL after his arrest, Serial Killer Rodney Alcala was discovered to have over a thousand photographs of various women and boys in his possession. In 2016, Alcala was charged with a 1977 murder after a dead woman was identified from one of the photos. Police are looking for help to ID more subjects.
6ENrw TIL Most people are not hypersensitive to cat fur, they are actually allergic to the saliva. When a cat grooms themselves, these allergens are placed on the fur. The saliva contains different major and minor allergens which can cause sneezing, congested eyes and blocked nose.
rwrM TIL there is a single ATM in Antarctica, operated by Wells Fargo Bank. It takes Wells Fargo ten months to prepare to service its ATM, and the employee sent must undergo a psychological evaluation in case they are stranded in Antarctica when flights are cancelled for the season.
DQwBg TIL that Zambia produces the most emeralds in the world. Between 2016 and 2020, the country produced 129,400 kilograms of emerald gemstones. Emeralds from Zambia have grown in popularity due to their level of clarity, the depth of their color, and their tendency to be stronger than other emeralds
LkNb0 TIL in 1875 three French men traveled to a height of 28,000ft in a balloon. When it landed only one man remained alive and was permanently deaf.