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9Ybn7 TIL People such as astronomers who spend a lot of time in dark environments prefer to use red lighting when they need just a little light. Eyes are less sensitive to red light and they are less likely to mess with the dark-adaption of our eyes
7rykZ TIL Reflector telescopes can have varying focal ratios to keep the optical tube size manageable. The largest privately owned reflector telescope has a 75” mirror, is mounted on a trailer and is pulled by a truck