Talk:Season/DaysAtPoles draft

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search

The fluctuations in the amount of sunlight are more pronounced at higher latitudes. The Equator does not have any noticeable fluctuation at all, while the North Pole and South Pole have extreme fluctuations. At the exact poles, the sun rises slowly from late spring through early summer, reaching its apex in the middle of summer, and gradually sets through the rest of summer and early fall. Outside those times, it is below the horizon, resulting in several weeks of "twilight" in the late autumn and "dawn" in the early spring and many weeks of near darkness, climaxing in the middle of winter. The sun essentially does not appear to move at all during a 24-hour period. This is sometimes described as being one "day" and one "night" with one sunrise and one sunset; this is accurate only if one realizes that it is equivalent to a normal 24-hour day-and-night cycle stretched evenly over a 365-day period.

Any point above the 60th parallel has one period during the summer during which the sun never dips below the horizon, and one period during the winter during which the sun does not rise above the horizon. At progressively lower lattitudes, the periods of "midnight sun" (or "midday dark" for the other side of the globe) are progressively shorter, and the sun appears to move more and more in the sky during a 24-hour period, such that near the pole the midnight sun lasts for weeks but further south it is less and less until, below the 60th parallel (in the north, or above the 60th in the south), the sun always goes below the horizon and rises above it once during each 24-hour period.

Example[edit]

At the military and weather station called "Alert" on the northern tip of Ellesmere Island, Canada (about 450 nautical miles from the North Pole), the sun simply appears to make a small circle in the sky during each 24-hour period, all year long.

Before mid-April, that small circle takes place below the horizon, so the station is more or less in darkness. In mid-April, the sun's small circle begins to peek above the horizon before dropping back out of sight, and each day it climbs a bit higher, and stays up a bit longer. However, mid-April is not first light. The sky (as seen from Alert) has been showing twilight, or at least a pre-dawn glow on the horizon, for increasing hours each day, for more than a month before that first sliver of sun appears.

In the weeks surrounding June 21, the sun is at its highest, and it appears to circle the sky without ever going below the horizon. Eventually, it does go below the horizon, for progressively longer and longer periods each day until, around the middle of October, it disappears for the last time. For a few more weeks, "day" is marked by decreasing periods of twilight. Eventually, for the weeks surrounding December 21, nothing breaks the darkness. In later winter, the first faint wash of light briefly touches the horizon (for just minutes per day), and then increases in duration and pre-dawn brightness each day until sunrise in April.