The apparent motion of the Sun across the sky is a result of two primary factors: the Earth's rotation on its axis and the Earth's orbit around the Sun.
Earth's Rotation: The Earth rotates on its axis, completing one full rotation in approximately 24 hours, which we perceive as a day. As the Earth rotates, different parts of its surface come into view of the Sun, creating the cycle of day and night. From an observer's perspective on Earth, the Sun appears to rise in the east, move across the sky during the day, and set in the west.
Earth's Orbit: Simultaneously, the Earth orbits the Sun in an elliptical path, taking approximately 365.25 days to complete one revolution. This orbit is slightly tilted relative to the Earth's axis, resulting in the changing seasons. As the Earth orbits the Sun, the Sun's apparent path across the sky also shifts gradually.
The apparent path of the Sun across the sky, known as the ecliptic, is not a perfectly straight line but rather an arc that changes its height and position throughout the year. This path is determined by the tilt of the Earth's axis, which causes the Sun's rays to strike different latitudes at different angles as the seasons change.
During the Northern Hemisphere's summer, the Sun appears higher in the sky and takes a longer and higher path across the sky. In contrast, during winter, the Sun appears lower in the sky, and its path is shorter and lower. This variation in the Sun's path is responsible for the differences in daylight duration, intensity, and temperature between seasons.
In summary, the Sun's apparent motion through the sky is a combination of the Earth's rotation on its axis, which causes the daily cycle of sunrise and sunset, and the Earth's orbit around the Sun, which results in the changing position of the Sun along the ecliptic throughout the year.