What causes the seasons?

What causes seasons? Weather cycles through the four seasons like clockwork. But what is the reason behind these seasons, and why are the changes so consistent? The answer comes from Earth’s slight tilt on its axis, about 23.4 degrees on average relative to its orbital plane. This angle changes the amount of light each hemisphere receives as Earth revolves around the Sun. When the North Pole is pointed toward the Sun, it exposes the Northern Hemisphere to more light, resulting in longer and warmer days than those in the Southern Hemisphere, which receives comparatively less light as a tradeoff. The pattern reverses every six months on days called equinoxes. This pair of dates occur when the hemispheres receive equal amounts of sun and mark the beginning of spring and fall. The equinoxes occur around March 21 and September 23, when the Sun is directly over the Equator. By contrast, summer and winter begin on the set of days known as the solstices. They occur when Earth’s axis is tilted at its most extreme relative to the Sun, causing days that are the longest and shortest of the year. The solstices take place around June 21, when the Sun is directly above the Tropic of Cancer, and December 21, when the Sun is directly above the Tropic of Capricorn. Because of the tradeoff between how much sun each hemisphere receives, seasons in the two hemispheres are always opposite of each other. For example, the June solstice marks the beginning of summer for the Northern Hemisphere and the beginning of winter for the Southern Hemisphere.