While seasonal changes in daylight hours are experienced throughout most of the earth, the Polar Regions experience more extreme changes because of their locations in relation to the sun during winter and summer. The axis or tilt of the earth account for Alaska and Antarctica’s extraordinary periods of extended hours of daylight and darkness.
To see why: imagine a tennis ball with a long needle passing through its center from top to bottom. The needle extends out both “poles” creating an axis. A black line that runs the circumference of the ball indicates the ball’s “equator.” Now imagine a roughly circular track for the ball to follow, and incline the axis 23.5 degrees towards the outgoing track, so that the ball is slightly inclined. Finally, place a light source in the center of this imaginary track.
As the ball moves around the track, its axis remains fixed, though by virtue of it moving around the track, its inclination, relative to the center light (the sun) changes. At one point along the track, the northern pole gets greater exposure to the light, being inclined inward, towards the light. At the opposite end of the orbital track, the same northern region is pointed away from the light source with the southern pole exposed “inward.”
This inclination of the earth is what creates our seasons, and is also responsible for Alaska's long summer days. When the North Pole is inclined inward towards the sun, the region receives extended exposure to the sun. From the viewpoint of someone standing at true north on the summer solstice, the sun raises high into the sky, and then circles the horizon without ever setting. Elongated exposure to sunlight during the summer season allows the region to retain more heat. Shadows are shorter because the sun is higher overhead.
At the South Pole in Antarctica, the opposite is occurring. Here, the region is inclined away from the sun, so that on the winter solstice, the sun skirts the horizons never quite rising. In outlying regions further from “true south” where the sun does raise low in the sky for short periods of time, the sun’s angle is very oblique. This creates longer shadows, additional atmospheric filtering, and weaker radiation or warmth. Thus, when Alaska is experiencing endless summer days filled with direct light, heat and warmth, desolate Antarctica is steeped in days of near total darkness and weak sunlight. Conversely, when Antarctica sees summer, Alaska is having winter. Because of its unique location, both winter and summer seasons are fascinating to experience in Alaska.
In spring and autumn seasons the earth’s axis is aligned along its orbital path, rather than towards or away from the sun. Hence, the sun shines most directly on the equatorial regions, or center of the earth. On the solstices that mark these seasons, March 21st and September 21st, we have 12-hour days and 12-hour nights. For each day that passes after a spring or fall equinox, the days begin lengthening in one hemisphere and shortening in the other.
Some people mistakenly attribute seasons to the slightly elliptical orbit of the earth, believing the closer the earth is to the sun, the warmer the season. In reality, earth’s orbit is nearly circular, and the small deviation in distance is not enough to cause seasons.