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About this tool
Work out when to leave to reach a viewpoint before golden hour, using NOAA solar equations for the light and Naismith's rule for the climb.
Calculates sunset, golden hour and the end of civil twilight for any latitude, longitude and date using the NOAA solar position equations, then works backwards through the climb with Naismith's rule — one hour per 5 km plus one hour per 600 m of ascent — to give the time you have to leave home. Sunset is solved at a zenith of 90.833 degrees, the standard allowance for refraction and the solar disc, and golden hour is taken as the sun between +6 and −4 degrees elevation.
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NOAA's published equations, not a fixed offset from sunset — golden hour length changes with latitude and season.
Ascent time and Langmuir's descent correction included, plus an honest pace factor for camera gear or children.
At high latitudes it tells you the sun does not set that day instead of returning a nonsense time.
Conventionally when the sun sits between +6 and −4 degrees of elevation, which straddles sunset itself. Its length depends entirely on latitude and season: in London in late June it runs about 80 minutes, while near the equator it can be under 40, because the sun drops through those degrees almost vertically.
Until civil twilight ends, when the sun reaches 6 degrees below the horizon — enough light to walk and read outdoors without artificial light. In mid-latitudes that is roughly 30 to 45 minutes after sunset in summer and shorter in winter; in the tropics it can be under 25 minutes. Past that point you need a torch on any rough ground.
Naismith's rule, published in 1892: allow one hour for every 3 miles (5 km) of distance, plus one extra hour for every 2,000 feet (600 m) of ascent. Langmuir's correction adjusts for descent — subtract 10 minutes per 300 m on moderate slopes of 5 to 12 degrees, add 10 minutes per 300 m on anything steeper. The rule assumes fit walkers, good ground and no significant stops, so add a margin for anything else.
At least 20 to 30 minutes before golden hour starts, which is roughly an hour before sunset in mid-latitudes. That leaves time to find the actual composition rather than the first gap in the trees, and covers the walk being slower than planned. Always plan the descent as well — the light after golden hour goes quickly, and a route that was obvious on the way up rarely is on the way down.