The Winter Solstice

Solstice Defined

The solstice is a moment when the sun reaches an extreme point in the sky, resulting in the longest or shortest day of the year, depending on your location. Gary Arndt explains that this phenomenon is recognized by almost every culture due to its significance in tracking the sun's path 1. While commonly referred to as a day, the solstice is actually a precise moment that can be pinpointed to the second. There are two solstices each year, one in winter and one in summer, determined by the Earth's poles pointing at their maximum angle towards or away from the sun 1.

   

Axial Tilt

The Earth's axial tilt is crucial for the occurrence of solstices and seasons. Gary Arndt describes how the Earth's axis is tilted approximately 23.4 degrees off the ecliptic plane, leading to the variation in sunlight received throughout the year 2. This tilt, combined with the consistent orientation of the poles, results in the changing seasons. Without this axial tilt, there would be no seasons, and one pole would experience perpetual light while the other would be in constant darkness 2.

   

Earth's Wobble

The Earth's axial tilt and its slow wobble, known as precession, cause gradual changes in the timing and intensity of seasons. Gary Arndt explains that the Gregorian calendar helps keep solstices and equinoxes at roughly the same time each year, but minor adjustments may be needed in the distant future 3. Over thousands of years, the tilt of the Earth changes, affecting the extremity of seasons and the positions of the tropics and polar circles. Currently, the Earth's tilt is decreasing, leading to less extreme seasons over time 3.