Chapter 2, Problem 1RQ

To determine

The way in which tilt of the Earth on its axis causes seasons.

Answer to Problem 1RQ

Inclination of the axis is the primary cause of the seasons. The orientation of the Earth to the Sun changes continuously when it travels along its orbit, and it results in a seasonal variation. The axis of the Earth is not perpendicular to the plane of its orbit around the Sun. Instead, it is tilted $23{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}^{\circ }$ from the perpendicular, and it is known as the inclination of the axis.

Explanation of Solution

A major factor that causes seasons is the gradual change in the angle or altitude of the Sun above the horizon. The amount of energy that is received at the surface of the Earth is influenced in two ways by the seasonal variation in the angle of the Sun above the horizon. Primarily, the solar rays became the most concentrated and thereby most intense when the Sun is directly overhead. When the angles are less, they spread out and the intensity of solar radiation that reaches the surface becomes less.

In addition, the path that is taken by the rays of the Sun when they pass through the atmosphere depends on the angle of the Sun. When the position of the Sun is directly overhead, then the solar rays strike the atmosphere at an angle of 90 degree, and it travels to the shortest possible route to the surface. However, to reach the surface, the rays that enter at a 30-degree angle should travel twice of this distance, whereas the rays that have a 5-degree angle is able to travel through a distance that approximately equals the thickness of 11 atmospheres. When the length of path is longer, then the chance for sunlight to disperse by the atmosphere is higher, and it reduces the intensity at the surface.