Question

why norway is called the land of midnight sun

Answer 1

Due to Norway's high latitude, there are large seasonal variations in daylight. From late May to late July, the sun never completely descends beneath the horizon in areas north of the Arctic Circle (hence Norway's description as the "Land of the Midnight Sun") and the rest of the country experiences up to 20 hours of daylight per day. Conversely, from late November to late January, the sun never rises above the horizon in the north, and daylight hours are very short in the rest of the country.

Answer 2

Due to high latitude in Norway, 60 deg North in the northern hemisphere, the Sun is visible even at midnight hour during middle of the summer.  That is why it is called the land of midnight summer.  There is darkness for very little time during summer and light for almost the entire day.