Evening civil twilight is the period from sunset until the sun is 6¡ below the horizon. 

Evening nautical twilight begins when the setting sun is 6¡ below the horizon, and ends when the sun is 12¡ below the horizon. 

Evening astronomical twilight begins when the sun is 12¡ below the horizon, and ends when the sun is 18¡ below the horizon. 

Morning astronomical twilight begins when the rising sun is 18¡ below the horizon; 

morning nautical twilight begins when the rising sun is 12¡ below the horizon, 

and morning civil twilight begins when the rising sun is 6¡ below the horizon.