Sunrise, Sunset And Daylength For Any City. Global Monitoring Laboratory Earth System Research Laboratories. National Oceanic and Atmospheric Association. Seasonal variations in daylight, twilight, and darkness. And if you're excited about taking pictures after dark, check out Night Sky Photography: From First Principles to Professional Results by Adam Woodworth (Ilex Press, Feb. Or, take a look at this photo from NASA that shows the gradual transition from day to night through all the stages of twilight, as seen from the International Space Station. You can use this mapping tool from to find out where on Earth is experiencing astronomical twilight right now. Noctilucent clouds become visible at twilight because the sun's light can still reach their high altitudes, highlighting them in a blue or silvery light against a dark sky, horizon and ground. Unlike cirrus clouds, which look similar but form in the high troposphere, noctilucent clouds appear near the polar regions in the thin, frigid air of the mesosphere, some 53 miles (85 kilometers) above sea level. Noctilucent clouds are wispy, high-altitude collections of ice crystals best viewed when the sun is between 6 and 16 degrees below the horizon, according to the World Meteorological Organization (WMO). Related: Planets align over the 'White City' in twilight photo of Tel Aviv In fact, some features are best viewed and photographed before full dark, like city skylines and noctilucent clouds. (Image credit: Moonshot11 via Getty Images)Įven though the night sky isn't at its absolute darkest during astronomical twilight, plenty of photographers find it a good time to take pictures of the heavens. Noctilucent clouds are interesting skywatching targets during astronomical twilight. How do astrophotographers handle astronomical twilight? During nautical twilight, wrote the NWS, sailors could both see the horizon and pick out recognizable stars at the same time, leading to reliable readings and a better idea of where they were headed in a featureless sea.Ĭivil twilight describes the time just after sunset, before the sun reaches 6 degrees below the horizon, or just before sunrise when the sun is above 6 degrees below the horizon. According to the NWS, its name describes its use in navigation at sea. Nautical twilight occurs before astronomical twilight in the evening and before astronomical twilight in the morning when the sun's geometric center is between 6 and 12 degrees below the horizon. Together, astronomical, nautical and civil twilight describe the time between sunset and full dark, and between full dark and sunrise. (Image credit: TWCARLSON/WIKIPEDIA/CC BY-SA 3.0.)Īstronomical twilight is the darkest of the three types of twilight. There are three types of twilight, depending on where the sun is in relation to the horizon. What's the difference between astronomical, nautical and civil twilight? Time and Date's sun calculator gives exact time intervals for astronomical twilight for any location on a given date.The calculator from Cambridge in Colour provides the time that the sun reaches 18 degrees below the horizon anywhere on Earth - the after-dusk end or pre-dawn beginning of astronomical twilight.The National Oceanic and Atmospheric Administration (NOAA) hosts a calculator that will give the exact time of sunset and sunrise anywhere on Earth, but you may have to use NOAA's data to calculate astronomical twilight yourself.gives the exact start and end times of astronomical twilight for any location on a given date.If you're curious about astronomical twilight in your area, you can use one of several different calculators to find out when it will occur: In fact, according to a 1931 paper published in the journal Geographical Review, all three twilight conditions (civil, nautical and astronomical) take no longer than 2 hours and 11 minutes at the equator on the equinox. That's because the Earth spins at a slight angle compared to the plane of its orbit around the sun, creating the planet's seasons - during winter in the northern hemisphere, the north pole is angled away from the sun, so the sun lingers between 12 and 18 degrees below the horizon for a long time.Īt the equator, however, astronomical twilight is a much shorter period. For example, in winter close to the north pole, astronomical twilight can last for weeks, spanning from late October to mid-November and returning once again in January, wrote astronomer Joe Rao for.
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