Final answer:
The higher the latitude, the more days occur where the sun does not set, particularly during the summer solstice in regions near either the North or South Pole due to Earth's 23.5-degree axial tilt.
Step-by-step explanation:
The phrase that completes the sentence is: 'latitude.' The higher the latitude, the greater the number of days will be that the sun does not set. This phenomenon occurs because of the tilt of Earth's axis. During the summer solstice in the Northern Hemisphere, areas near the North Pole experience 24 hours of daylight, known as the midnight sun. Conversely, during the winter solstice, the sun does not rise for several days in these high-latitude regions, leading to polar night.
At high latitudes, the sun's path across the sky takes longer during summer, resulting in longer days. This is due to the Earth's 23.5° tilt and its orbit around the sun. The tilt causes the sun to be above the horizon for extended periods in places far from the equator, especially near the poles.
The opposite occurs in the Southern Hemisphere, where during its summer solstice, locations near the South Pole experience continuous daylight, while during its winter solstice, they endure extended periods of darkness.