Notes: Fri 13 Sept

The Sun's Energy

altitude= angle of solar elevation = angular difference between horizon and sun

subsolar point= zenith= point directly beneath sun (where sun's rays are perpendicular to the Earth's surface). This point migrates between the Tropic of Capricorn and the Tropic of Cancer.

declination= angular distance between equator and subsolar point.

Similar to figure 5.8 in text - shows contours of energy received at different latitudes and times of the year. Note that poles get little energy; most energy is at the equator. Why is there more energy received in the southern summer than the northern summer? Because the distance to the sun is different at those two times. Remember Earth is closer to the sun during the northern hemisphere winter.

More on the sun's energy
Most of the sun's energy is in the form of light. Visible light is part of the electromagnetic spectrum. Electromagnetic energy is transmitted through waves made of an electrical field interacting with a magnetic field. This wave has a wavelength and an amplitude. The sun's energy is strongest in the blue visible light wavelength.

The Atmosphere

The atmosphere is the moveable gaseous body around Earth with the ability to distribute heat and moisture. We know it as "air," an odorless, colorless (except when there's pollution), tasteless mix of gases. It screens and selectively transmits solar and terrestrial radiation, and diffuses, scatters, absorbs,and retransmits electromagnetic radiation.

composition: N2 78%, O2 20.9%, and Ar 0.93%, plus trace gases. The main gases are also called the constant gases and total 99.83% of the atmosphere. Note that nitrogen and argon are inert while oxygen is not and is important for life. The trace gases include:

The atmosphere has weight, and it is compressed by gravity. That explains why air is denser at the Earth's surface. As you go away from Earth's surface, the density of air drops off exponentially similar to the way gravity does. Most of the air is in lower levels.

Back to GS 201 homepage