THE REASON FOR SEASONS Earth’s four seasons (the amount of daylight and the temperature) are caused by its orientation to the sun. The orientation is related to its orbit around the sun, its rotation on its axis, and the degree its axis is tilted. Earth rotates counterclockwise on its axis once every 24 hours, creating day and night. Earth orbits the sun in a 365-day cycle. Earth’s axis is tilted at an angle of approximately 23.5°. This angle remains constant throughout its rotation and orbit. The distance between Earth and the sun varies slightly during its orbit, however this distance has little impact on seasons. Instead it is the tilt of Earth on its axis and the orientation of the axis to the sun that creates variations in daylight and temperature, creating seasonal variations. In summer, when the northern hemisphere is tilted toward the sun, it receives a greater amount of solar energy, and therefore experiences warmer temperatures and increased daylight. In winter, when the region is tilted away from the sun, a reduction in solar energy leads to cooler temperatures and reduced daylight. About June 21st, the northern hemisphere is tipped directly toward the sun. Known as summer solstice, this date marks summer’s beginning. For most of the hemisphere it is the day of the year with the longest period of daylight. About September 22nd, Earth has moved around the sun so the poles neither point towards nor away from the sun. This is known as the autumnal equinox, when the entire planet experiences 12 hours of daylight and 12 hours of darkness. This marks the beginning of fall, or autumn. The winter solstice occurs about December 21st when Earth is oriented so the North Pole is facing away from the sun and the South Pole into the sun. Northern regions experience the shortest period of daylight on this “first day of winter.” About March 20th, begins the spring equinox. Earth is similarly positioned to that which occurs in September, only on the other side of the sun. Again, the orientation produces 12 hours of daylight and 12 hours of darkness, and signals the beginning of spring, or the vernal equinox.