At the Earth’s poles, the transition periods of sunset and sunrise are markedly different from what is experienced elsewhere. During an equinox, around March 21 and September 23, the tilt of the Earth’s axis aligns such that both poles receive the same amount of daylight. This is when the poles experience their prolonged sunsets and sunrises.
At the poles, the sun does not set and rise in the rapid motion seen near the equator. Instead, because of the distinct tilt of the Earth and the way sunlight hits these regions, the sun takes its time to dip below or ascend above the horizon. This results in sunsets and sunrises that last about several days.
Specifically, the sun isn’t ‘on’ or ‘off,’ as it is in regions closer to the equator. Instead, during these periods, the sun slowly moves horizontally relative to the horizon, taking several days to complete. This means a slow, gradual twilight follows where the sun dips under the horizon for a brief moment and then rises again, or vice versa.
Also, atmospheric refraction extends the duration where the sun’s image is visible over the horizon before it has fully set or risen. It should be noted that around the solstices, one pole will have a prolonged period of daylight or darkness (polar day or polar night), leading to the phenomenon where the sun can be seen continuously for months during the summer, and it remains below the horizon throughout the winter.