Sunrise/Sunset Estimator

Sunrise and sunset times shift by minutes per day, more dramatically near the equinoxes, and depend nontrivially on your latitude. Looking up the exact time for a specific date and place means going to a weather site or running an astronomy library — overkill if you just need a rough number for trip planning or photography.

Provide latitude and date and the estimator returns sunrise and sunset times, plus day length and the change versus the previous day. Calculations use the standard NOAA solar position algorithm with a typical atmospheric refraction correction. Accuracy is within about a minute for most temperate latitudes and dates — fine for most practical use, less reliable extremely close to the poles where the math becomes unstable.

Does not account for terrain. If you're in a deep valley or behind a mountain, your visible sunrise will be later than the calculated one. The number returned is the geometric horizon time, which is what almanacs publish.

The NOAA solar position algorithm (also called Reda-Andreas algorithm in its full astronomical form, with simpler approximations sufficient for sunrise/sunset) computes the sun's position from the date, time, latitude, and longitude using astronomical formulas. The core math finds the sun's declination (its angle north or south of the equator on a given date) and hour angle (its position east or west of local meridian). Sunrise and sunset are when the sun's center crosses a chosen altitude — for "geometric" sunrise this is 0° (the horizon plus refraction correction of about 34 arcminutes), for civil twilight it's −6°, nautical −12°, astronomical −18°. The atmospheric refraction correction matters: it bends light around the horizon so the sun appears above the horizon when geometrically below it.

Worked example: latitude 40.7°N (New York City), date June 21 (summer solstice). Solar declination ~23.4°N. Day length is roughly 15 hours; sunrise approximately 5:25 AM local solar time, sunset approximately 8:31 PM. Now December 21 (winter solstice): declination -23.4°. Day length about 9 hours; sunrise around 7:17 AM, sunset around 4:31 PM. The dramatic seasonal swing depends on latitude — equatorial latitudes vary little (almost 12 hours year-round), polar latitudes go to 24-hour day or 24-hour night near solstices.

Limits the algorithm has: at high latitudes (above ~67° N or S during certain seasons), the sun stays above or below the horizon for entire days. The math has no real solution for sunrise/sunset on those days; the tool returns "sun does not set" or "sun does not rise" rather than an erroneous time. Atmospheric refraction varies with temperature, pressure, and humidity — the standard correction assumes typical conditions, and unusual atmospheric conditions can shift apparent sunrise by a minute or two beyond the calculation. Local terrain (mountains, deep valleys) adds further deviation; the tool computes geometric horizon, not visible-from-your-window horizon.

For practical applications: photography (golden hour, blue hour timing), trip planning (daylight remaining for hiking), gardening (daylight hours for plant growth), the tool is more than accurate enough. For navigation or precise scientific use, prefer dedicated astronomical libraries (NOAA's official tools, PyEphem, Astropy) that include corrections the simplified version omits. The simpler estimator gets you within a minute or two for most populated latitudes, which is sufficient for any decision a typical user is making.