Polar night — sun never rises (0 daylight hours)
Midnight sun — sun never sets (24 daylight hours)
Twilight seasons — the period when the sun both rises and sets (0 < daylight hours < 24)
These phenomena are defined astronomically by the sun’s altitude.
Polar Night occurs when the sun altitude never reaches 0° (the horizon), and Midnight Sun occurs when it never goes below 0°.
The periods shown here are an approximation, derived from daylight-hour calculations.
Source:
Open-Meteo.