...would I have to be so I spend 75% of the time in the dark as the earth spins? Imagine the sun shines on the earth in such a way that it casts a shadow that is at 60 degrees to the axis of the spin of the earth (Assume the Earth's axis is 0 degrees) as shown in my diagram below. I am trying to work out what 'latitude' (shown as P) I have to be at so I spend 75% of my time in the dark and 25% of my time in sun light as the earth spins about its axis. I am not looking for the actual latitude, but how to calculate d2 (diameter) and h2 (height) from below. Can anyone help? I've been at this for ages!