The duration of the twilight period between dawn and sunrise varies greatly depending on the [[observer]]'s [[latitude]], from a few minutes in [http://en.wikipedia.org/wiki/Tropics equatorial regions] to many hours in [http://en.wikipedia.org/wiki/Polar_region polar regions]. Dawn may easily be [[determined]] by observing a thread. When the color of a thread can be determined, changing from black to the threads distinctive [[color]], the 'crack of dawn' has occurred. This same measure of ambient light can be used to determine, conversely, the instant of 'dusk'.[http://en.wikipedia.org/wiki/Dawn] | The duration of the twilight period between dawn and sunrise varies greatly depending on the [[observer]]'s [[latitude]], from a few minutes in [http://en.wikipedia.org/wiki/Tropics equatorial regions] to many hours in [http://en.wikipedia.org/wiki/Polar_region polar regions]. Dawn may easily be [[determined]] by observing a thread. When the color of a thread can be determined, changing from black to the threads distinctive [[color]], the 'crack of dawn' has occurred. This same measure of ambient light can be used to determine, conversely, the instant of 'dusk'.[http://en.wikipedia.org/wiki/Dawn] |