New/Old Wind Chill Calculator Misconceptions in Meteorology: Bad. Weather Page for : Clear Sky Charts Local-National Dark Sky Convection. Note that the angles are not to scale so as to show the three twilight categories with more clarity. storm chasing, and Mount Washington-worst weather in the world. The figure below shows civil, nautical and astronomical twilight. But diffuse light sources such as galaxies, nebula, and globular clusters need to be observed under a totally dark sky, again when the sun is more than 18 degrees below the horizon. Point light sources such as stars and planets can be readily studied by astronomers under astronomical twilight. But to test the limits of naked eye observations, the sun needs to be more than 18 degrees below the horizon. Under astronomical twilight, the horizon is not discernible and moderately faint stars or planets can be observed with the naked eye under a non light polluted sky. In astronomical twilight, sky illumination is so faint that most casual observers would regard the sky as fully dark, especially under urban or suburban light pollution. ![]()
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