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Is there a relatively reliable way of calculating the time until sunset, without any specialist equipment, when I'm in the wilderness?

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A watch. You check when does the sun set. Subtract the current time from that and that's it. I guess error could be up to one hour because of the landscape (mountains). –  Vorac Jul 10 '12 at 10:01
    
@Vorac "You check when does the sun set" - and how exactly if you're in the wilderness? –  berry120 Jul 10 '12 at 11:29
    
First way - in the internet, before departing to the wilderness. You can also check how many minutes a day does that change. Second way - the first evening see at what time it sets. Of course, all this is provided you have a watch. –  Vorac Jul 10 '12 at 11:45
    
@Vorac The first way doesn't work if you've forgotten to check - and the second isn't much good on the first evening! –  berry120 Jul 10 '12 at 12:38
    
I live in a valley and I look at the shadow on the east mountains. When it is at the base it takes about 20-30 minutes for the mountains to be covered. At that point, I have about 15 minutes of "good" twilight that I can still ride at the skatepark with out it being dangerous. –  BillyNair Jul 16 '12 at 21:33

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up vote 7 down vote accepted

One method I've found to be particularly reliable is the finger method - hold your arm straight out in front of you, facing towards the setting sun like so:

Sunset diagram

Place your hand so your little finger is level with the horizon, and your fingers are stacked on top of each other. Each finger represents around 15 minutes of sunlight before the sun sets behind the horizon.

This method can be used relatively accurately up to two hours before sunrise, by using both hands.

See also this page.

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Which latitude have you tried this? It will have different results depending on where you are, eg where I grew up (quite far north!) a hand's breadth could give you hours before the sun set. –  Rory Alsop Jul 4 '12 at 8:39
    
@RoryAlsop This works well for me in the UK - I would imagine unless you're at the extremities, it works reasonably well. I've just checked the collins ultimate navigation manual where I got it from, and for this particular technique it makes no reference of it working better / worse in any particular place. –  berry120 Jul 4 '12 at 10:10
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In Orkney at midsummer, the sun doesn't go down so much as around - only briefly dipping under the horizon to the north. And north of the Arctic circle it won't go down at all in the summer. I wonder if it works at the equator... –  Rory Alsop Jul 4 '12 at 10:27
    
Winter vs summer and closer/farther from the equator has an impact on the accuracy of this technique (in the summer here it almost seems to hover above the horizon and skim to the right for a while before dipping lower). @berry120 - start with this technique and test it a few times in early then mid summer and then in the fall and winter to see the differences at your latitude. (fall and spring will be similar) –  BillyNair Jul 16 '12 at 21:29

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