[header] How to find out how much time is left before sunset [title] Find the location of the sun. [step] This method will work best if the sky is clear and there are no clouds. However, if it's cloudy, or the sun is obstructed by trees, you may have to approximate. 
[substeps] If it is cloudy and you can see a vague outline of the sun, you can still do the measurement between the horizon and the sun. There will be a haze around the sun in the clouds: use that haze as the position of the sun.