Nascer e Pôr do Sol (estimativa)
Estima horário aproximado de nascer e pôr do sol a partir da latitude e dia do ano (UTC).
Nascer / Pôr (UTC h)
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Estimating sunrise and sunset from latitude and day of year
A first-order estimate of sunrise and sunset leans on the solar declination delta and the hour angle H, tied together by cos(H) = -tan(latitude) * tan(delta). You take solar noon to be 12:00 UTC, then sunrise = 12 - H/15 and sunset = 12 + H/15, both in UTC hours and both before you've applied any time zone or equation-of-time correction. The method itself is ancient, traceable to Ptolemy's Almagest around 150 AD. Modern tools like the NOAA Solar Calculator run on the same idea, just with extra refinements layered on top.
Example: in Sao Paulo (-23.5 degrees) on June 21, sunrise lands near 06:45 and sunset near 17:30 in local time, once you fold in UTC-3 and refraction. That works out to about 10h45 of daylight.
Practical uses
Photographers chase the golden hour, the stretch right after sunrise and just before sunset, and the blue hour roughly 30 minutes before sunrise or after sunset, leaning on apps like SunCalc, PhotoPills and Stellarium. Islamic prayer schedules tie Fajr and Maghrib to civil twilight and sunset. Engineers at solar plants size battery storage and panel tilt against the sunrise and sunset bounds. And sailors and pilots still keep sunrise and sunset on hand as a celestial-navigation backup.
FAQ
Why does the result come in UTC? The simple formula pins solar noon to 12:00 UTC on the prime meridian. For your local clock time, add the longitude correction of 4 minutes per degree, plus your time zone offset.
What is the equation of time? It's the gap between true and mean solar noon, a correction of up to plus or minus 16 minutes over the year that comes from Earth's elliptical orbit and its axial tilt.
Why does my watch show sunrise slightly earlier than this estimate? Two things bend the timing: atmospheric refraction of about 34 arcminutes, and the Sun's own angular radius of about 16 arcminutes. Together they make sunrise look like it begins a few minutes before the geometric center actually crosses the horizon.
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