* Decently useful for outdoor purposes for me is somewhere in between civil and nautical twilight, I's say until -10° elevation. Once printed out, this may be sufficiently low tech to fulfil your needs. There are tons of such diagram generators available nowadays (they are used e.g. Some calculators calculate sunrise and sunset based on a so-called shadow file that gives the apparent horizon. Where you can see when (time & date) the sun is at what elevation (angle). More precise numbers can be read from a sun path diagram: You can use this together with twilight duration (from tables) to approximately adjust sunset for being in a deep valley (this approximatin becomes worse at high latitudes in summer - but then you have anyways very long days).Īctual twilight will be somewhere between the sun 6° below your apparent horizon (mountain range) and 6° below azimuth (astronomic horizon). Since daily changes are not that huge (not even far from the equator) and you anyways cannot plan day tours to the minute, noting maybe one day per week should be sufficient - that's a piece of paper that shoud fit into any outfit.Įnd/beginning of civil twilight is defined as the sun being 6° below the horizon. If you go somewhere far from your usual home, consider looking up sunrise/sunset and twilight (and maybe know the current moon phase and what that means in terms of moonrise and moonset) as part of planning your tour. If you have been at roughly this location for a while, knowing yesterday's sunset, maybe an approximate adjustment (like the 50° numbers I gave above) and the approximate duration of twilight shoud give you a decent idea. The daily shift in sunrise/sunset is about 3 min around equinox (and approximately 0 at solstice).This caught me many times, even when I was living in Northern Italy! Lighting conditions were reminding me rather too late to look for a place to stay for the night.) (At 40° N (north side of the mediterranean) twilight is only about half as long. In addition, we get a more than an hour of decently useful twilight* (until the sun is ≈10° below the horizon) all year round (± weather, vegetation, light pollution, obviously).the sun takes about 4 min from first hitting the horizon till being completely down.I live at about 50°N (quite central in Germany). horizon in the Soča valley can be +20° - +25° up. Again, I'd expect the effect to be the stronger, the further you are from the equator. Dark rain clouds can cost you several hours here (50 °N), snow or bright moonshine can make the whole night useful twilight.

useful twilight at the equator is maybe 20 min, but more than an hour at 50° and all night long in summer in Scandinavia.At the polar circles, that's true only at equinox - at solstice you have 24 h of day or night. at the equator, 12 h day/night is a decent approximation all year round.Latitude has a huge influence on how long the sun takes to travel a given vertical angle (declination): Some places of course use time zones other than the 'naturally closest one' and/or daylight saving time. Longitude and local time zone: very much as a rule of thumb, your position within the current time zone makes a difference of ☓0 min. The further you are from the equator, the more prominent is this effect. There are a number of influencing factors, and the further you are from the equator, the more important they get:

Time until sunset