Areas in the tropical regions receive sunlight directly. Regions further north and south receive incoming solar radiation at an angle, which reduces the heat and energy that reaches these areas.
The sunlight intensity on some parts of the earth significantly varies over the course of the year as the earth changes its orientation in space. Seasonal variation in solar input occurs because the Earth is tilted on its axis by 23.5˚. As Earth orbits the sun, its orientation to the sun changes.
Winter in the northern hemisphere occurs as the northern tip of the planet tilts away from the sun. During this time, the southern hemisphere receives greater solar input and experiences summer. As Earth reaches the opposing point of its orbit and the northern hemisphere becomes angled toward the sun, the seasons reverse. Tropical regions experience relatively minor changes in temperature, and their seasons are characterized by the presence or absence of rain.