# I have a compass but no watch, how can I tell when it will get dark?

I was reading all of the answers to Are there any situations while backpacking that would require a watch? and surprised at the number of answers that said you need a watch so you would know how long until dark. People have been walking around the world for a very long time, portable time pieces have only been readily available for about hundred years. They do have a longer history but spent much of that time as very high end luxury items.

The compass has a much longer history, it is simpler instrument, with a much lower cost to acquire and maintain.

A watch alone, will not tell you when it going to get dark, nor when the tides will be low, but combined with other information it can help you determine when the forecast event will occur.

If I have a compass, how can I use it to estimate how long until sun set?

• The compass and your shadow can tell you when it is noon. Then if you know the date, you can estimate your latitude from the length of your shadow. Time from noon to sunset is a function of date and latitude. – WGroleau Feb 25 '17 at 12:06
• @WGroleau a few more details and that could be an answer.... :) – James Jenkins Feb 25 '17 at 12:08
• When I geta better internet connection, perhaps. :-) – WGroleau Feb 25 '17 at 12:41
• My understanding of this is that while it can be done, it requires more tables and math than I would like to do in the outdoors. – Charlie Brumbaugh Feb 25 '17 at 17:39
• @BenCrowell one example To know when it's going to get dark! – James Jenkins Mar 1 '17 at 17:16

You don't need a compass, nor any mechanical tool at all. You just need your fingers. I've linked an article with illustrations at the end, but here is the basic idea:

1. Stand facing the sun, extend your arms out fully, and bend your hands inward.
2. Rotate your fingers to be parallel to the horizon, and move your hand(s) to position them between the horizon and the sun.
3. Count how many fingers are between the horizon and the bottom of the sun.
4. Each finger means 10 to 15 minutes (different sources give different estimates, my own experience doing this is closer to 10.)

As pointed out in comments, this technique only gives an approximation. Its usefulness may depend on terrain and even your latitude.

Here's the article: How to Find Out How Much Time Is Left Before Sunset.

• This method will beat a watch anytime in mountain or canyon areas where sun's path is intercepted by the terrain. – Charlie Brumbaugh Feb 25 '17 at 17:49
• This answer is wrong, as is the linked wikihow page. As an extreme example, if you're above the arctic circle, then it could be 6 months until sunset. This kind of thing depends on both the latitude and time of year. – Ben Crowell Feb 25 '17 at 21:15
• @BenCrowell It's an excellent approximation technique. As most people in the outdoors don't need to know the exact time, this method will work fine for most of them. – Charlie Brumbaugh Feb 25 '17 at 21:44
• @CharlieBrumbaugh: No, it's not an excellent approximation technique if it tells you the sun will set in 1 hour and actually it will set in 6 months. – Ben Crowell Feb 25 '17 at 23:29
• If you are one of the 0.053 percent of the human population that lives above the arctic circle then yes it might throw you off. However, for the vast majority of the population its is a good approximation to at least a quarter hour or so. – Charlie Brumbaugh Feb 25 '17 at 23:36