My family and I want travel somewhere with polar night. I looked up Tromsø, Norway.
"Down all day" beneath means 24 h darkness, no sun and thus no sun-light. Right?
But if no sun and sun-light, why's there still twilight?
Civil twilight: the sun is between 0 and 6 degrees below the horizon
Nautical twilight: the sun is between 6 and 12 degrees below the horizon
Astronomical twilight: the sun is between 12 and 18 degrees below the horizon
I believe if the sun is lower than 18 degrees below the horizon, all sun rays can no longer reach your location. Hence it is completely dark.
From an human eye perspective.
Civil twilight=you will be able to read a newspaper.
Nautical twilight=you will be able to see the contours of mountains and the brightest stars will be visible.
Astronomical twilight=you will no longer be able to see the contours of mountains and the atmosphere will have a very dark color,lots of stars are visible.
Night=the sky is black and all of the stars are visible you will need additional light to be able to find your way(all of this is for areas with no manmade illumination)
Twilight occurs when the sun is just slightly below the horizon. You cannot see the sun but light will still be available due to atmospheric processes. The different stages of twilight depend on the angle of the sun to the horizon leading to different degrees of darkness.
Down all day just means that the sun will never pass the horizon. But twilight may still occur since around midday the sun will still be close to the horizon.