Weather refers to short-term atmospheric conditions in a small area that can change rapidly, while climate describes long-term patterns over 100+ years in a large area that changes very slowly. Seasons are caused by the tilt of the Earth's axis of rotation relative to its orbit around the sun, which determines how direct sunlight strikes each hemisphere over the course of a year. The summer solstice marks the longest day of the year when the sun's rays are most direct, while the winter solstice is the shortest day with the most indirect sunlight.