The Earth-Sun Relationship

A look at the Earth-Sun system provides important insight into current environmental phenomena. Since the beginning of the Earth's evolution four and a half billion years ago, the atmosphere and landscape have changed significantly. Today, global atmospheric problems such as global warming and ozone depletion arise from changes in the delicate balance of the Earth's atmosphere that alter the amount of the sun's radiation reaching humans and other living creatures. The Earth's immediate physical environment is patterned by three primary influences:

  1. The nearness of the sun.

  2. The Earth's atmosphere, a mixture of gases held in a layer surrounding the Earth by the Earth's gravitational force. This layer has reached the current and somewhat steady composition of approximately 80% nitrogen and 20% oxygen over the last four and a half billion years.

  3. The composition of the solid mass of the Earth, which gives rise to the materials in and on the Earth (including water, an essential to our type of life). Also resulting from the composition and manner of the origin of the Earth is the temperature of the Earth's core.

This section will focus predominantly on the first two influences: the Earth's atmosphere, and the Earth's relationship to the sun.

From a physical point of view alone, the Earth-Sun system can be represented simply as in Figure 1. The two main forces and effects of the sun on the Earth are the gravitational force (maintaining the Earth in an orbit around the sun), and the electromagnetic radiation from the sun (keeping the Earth's atmosphere at a particular temperature).

Figure 1: Earth-Sun system with primary influences.

Different components of the sun's (solar) spectrum interact with the atmosphere. Over billions of years, this interaction has produced both the ozone layer and current climatic conditions with feedback from life that evolved. These phenomena form the major topics of this unit. We begin with a description of solar radiation.