Introduction to Global Weather

In a previous section, we have seen the Sun as the source for our weather through the transfer of heat energy to the Earth. The equatorial region receives the bulk of the heat energy but not always directly. Because, relative to the Sun, the Earth's axis is tilted approximately 23½°. This tilt means the amount of radiation any one place receives varies over the course of a year.

This tilt in the Earth's axis combined with the orbit around the Sun is responsible for our seasons. The Northern Hemisphere winter (December through February) occurs when the Earth's North Pole axis points away from the Sun.

This places the South Pole's axis pointed toward the Sun exposing the Southern Hemisphere to greater heat energy, and therefore, Summer. During these three months, daylight hours are shortest for the Northern Hemisphere and Longest for the Southern Hemisphere.

Six months later, the Earth has completed one half an orbit around the Sun and the seasons are reversed. In June, July and August, it is Summer in the Northern Hemisphere and Winter in the Southern Hemisphere. The length of daylight hours is also switched with the longest daylight hours in the Northern Hemisphere and shortest in the Southern Hemisphere.

Twice a year, March 21 and September 23, both hemispheres receive the same amount of radiation. These two days are called the equinox meaning equal night where Both hemispheres have 12 hours of daylight and darkness.

Learning Lesson: The Shadow Knows I

Learning Lesson: The Shadow Knows II