![]() When someone refers to "midnight tonight" or "midnight last night" the reference of time is obvious. Is midnight the end of a day or the beginning of a day? ![]() Hours of operation for a business or other references to a block of time should also follow this designation rule.įor example, a business might be open on Saturdays from 8 a.m. The same is true for midnight, but there is an added issue of which day midnight refers to (see below). as soon as it the 12:00 appears, and not delay the display of the p.m. For example, it would be applicable for a digital clock changing from 11:59:59 a.m. It is fair to say, however, that the shortest measurable duration after noon should be designated as p.m. Also, midnight is both twelve hours before noon and twelve hours after noon. Since noon is neither before noon nor after noon, a designation of either a.m. To illustrate this, consider that "a.m." and "p.m." are abbreviations for "ante meridiem" and "post meridiem," which mean "before noon" and "after noon," respectively. This is a tricky question because 12 a.m. ![]() What are the definitions of dawn, dusk and twilight?Īre noon and midnight referred to as 12 a.m.When do sunrise and sunset occur throughout the year?.Is midnight the end of a day or the beginning of a day?.Are noon and midnight referred to as 12 a.m.Note that the angles are not to scale so as to show the three twilight categories with more clarity.Sunrise/sunset times and definitions of dusk/dawn/twilight. 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. Begins in the morning, or ends in the evening, when the geometric center of the sun is 18 degrees below the horizon.Nautical Twilight is also known as Nautical Dawn and Nautical Dusk. Absent fog or other restrictions, outlines of terrestrial objects may still be discernible, but detailed outdoor activities are likely curtailed without artificial illumination. ![]() In general, the term nautical twilight refers to sailors being able to take reliable readings via well known stars because the horizon is still visible, even under moonless conditions.
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