# Mathematically calculated sunrise and sunset with GPS

In the GPS Altimeter app, sunrise and sunset are automatically calculated with a proprietary mathematical algorithm based on the current GPS coordinates. No internet connection is required, so you will always know at all times when it gets dark.

## Plan your excursion to the fullest: calculating the timing of an excursion

### Know exactly when the sun will set, it allows you to better plan your excursion.

The duration of the excursion (or of the various phases, from stage to stage) can be taken from the hiking guides, from the websites where we found information (if shown), from the signs and indications we find on the spot, always bearing in mind that , errors aside, the times are still subjective. The times shown on the signposts are generally medium or medium-high, or very often with a good workout you can stay below. Unfortunately sometimes they must be taken with the benefit of inventory as it happens that the signs show indications that are not entirely correct (signs moved from place to place without regard to timing, glaring errors, etc.), if you notice you will find “correct” (plates glued on top of the original writing). If you ask for advice to mountain guides or excursionists also budgeted to multiply their times by 1.5 at least because they always have a quick pace 🙂

If, on the other hand, we cannot find indications on the timing of the excursion, the only thing to do is to get them by studying the map. The general indications found on internet sites and / or excursion guides are generally always the same and, as far as I am concerned, quite apt. Generally it is said that a hiker manages to overcome (uphill) an altitude difference of 300-400 meters per hour and a distance of about 2-4 Km.

This can be verified also experimentally taking as an example some excursions of this site but let’s remember that these ARE ALWAYS MEDIUM AND INDICATIVE VALUES since the time of ascent depends on the type of path, from the physical conditions and from the training of the excursionist, from the conditions environmental and meteorological factors and countless other factors. In principle and in the absence of other indications, however, they allow us to estimate the duration of the excursion, remembering that the difference in altitude exceeded in 1 hour increases if the route is steep (it is said that “it rises quickly to altitude”) while the distance traveled per hour increases if the route is not very steep (in which case the difference in level exceeded in 1 hour is also little, compared to the aforementioned 300 meters).

## Practically:

if the route is moderately steep (for many excursions or excursions it is so) the indication of 300-400 meters / hour is correct, if it is very steep it would also be necessary to hypothesize 450-500 meters / hour and the indication of 2- 4 Km / hour becomes less reliable.

If the path is less steep (extreme case: plateau or long stretches on a slight slope, with modest gradients), the indication of 300-400 meters / hour of difference in height is almost meaningless and it is necessary to look at the distance assuming calmly 4 Km / hour .
Let us not pose the problem of real or topographical distance because the difference is still small, given the approximation of these calculations. However, we will have to consider whether the path climbs straight (the real distance is almost the same as the crow flies between start and finish) or a winding path (the real distance is much greater than the crow flies).

In the latter case we should consider the real distance (but it would probably be more accurate to calculate the time based on the difference in height because the path will be steep). If the excursion is long (climb over 4 hours), it is necessary to consider the fatigue for which the times can be further extended.

The descent time is generally considered equal to 2/3 of the ascent time, obviously it can be even less if the route is steep. Even this evaluation, we have verified, is almost always correct.

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