What aspect of sunlight varies with the change in seasons?

The duration of sunlight varies with the change in seasons due to the tilt of the Earth's axis and its orbit around the sun. As the Earth orbits the sun, different parts of the Earth receive varying amounts of sunlight at different times of the year. During summer months, regions experience longer daylight hours because the North or South Pole is tilted towards the sun, resulting in more hours of sunlight. Conversely, during winter months, the pole is tilted away from the sun, leading to shorter days.

This variation in duration directly affects the solar energy that locations receive throughout the year, influencing temperature and weather patterns. While the angle and intensity of sunlight are also factors in seasonal changes, the duration is what varies most distinctly as day length changes dramatically from summer to winter. Thus, the duration of sunlight is a clear indicator of the seasonal changes experienced on Earth.