Which latitude mark defines the Antarctic Circle?

The Antarctic Circle is defined at latitude 66.5 degrees south. This line marks the point where, at least once a year, there is a 24-hour period of continuous sunlight in the summer and a 24-hour period of darkness in the winter for locations south of this latitude. The positioning of the Antarctic Circle is significant because it directly correlates to the tilt of the Earth's axis at approximately 23.5 degrees, which affects the amount of sunlight and duration of day and night experienced in polar regions.

Understanding the latitudinal divisions helps break down Earth's climate zones, with the regions inside the Antarctic Circle experiencing polar climates characterized by extreme variations in daylight throughout the year, contrasting sharply with the experiences of regions near the equator or other latitudes.