What Makes a Season?

A season is one of the major divisions of a year on Earth. Each season is marked by an annual change in weather. Seasons occur because the Earth’s axis is tilted in relation to the Sun. This tilting is what creates the four seasons of the year - spring, summer, autumn (fall) and winter. Since the axis is tilted, opposite parts of the Earth are positioned to receive more direct rays from the Sun at different times of the year.

Why Do Seasons Occur?

Seasons result from the yearly path the Earth travels around the Sun in combination with the tilt of the Earth’s axis. In temperate and Polar Regions, the seasons are marked by changes in the energy of the Sun’s rays that reach the Earth’s surface and changes in the length of days and nights. Differences in the strength of sunlight may cause animals to go into hibernation or to migrate, and plants to become dormant.

During June, July, and August, the northern hemisphere is exposed to more direct sunlight because the northern hemisphere is tilted toward the Sun. This tilt toward the Sun makes the energy from the Sun stronger and warmer when it hits the northern hemisphere. The southern hemisphere is exposed to less direct sunlight during this time because it is facing away from the Sun. Also, during this time, days are longer and nights are shorter in the northern hemisphere since the Sun is at a higher angle in relation to the Earth. The same is true of the southern hemisphere in December, January, and February. The combination of longer days and more direct sunlight creates the warm summer season whether in the northern or southern hemispheres. Generally there are four recognized seasons in temperate and Polar Regions: spring, summer, autumn and winter.

Special Seasons

In most tropical and subtropical regions, especially near the Earth’s Equator, there are commonly only two recognized seasons. These are the rainy (wet or monsoon) and the dry seasons. Because the angle that sunlight hits the Equator does not change much over the year, the tropical and subtropical regions enjoy twelve hours of daylight and twelve hours of night year round. The strength of the Sun’s rays that reach these regions also stays constant throughout the year, so average temperatures stay very constant. However, the amount of rain and precipitation the areas receive changes throughout the year. Rather than having seasons based on the average temperature, as is true in the temperate and Polar Regions, seasons in the tropical and subtropical regions are based on how much rainfall generally falls during periods over the year. For example, in Central America, the dry season is called summer (Oct to May) and the rainy season is called winter (Apr to Nov) even though it is located slightly north of the Equator in the northern hemisphere and temperatures stay very constant.

In many areas of the world, local or special "seasons" have been created to celebrate events such as planting or harvesting of crops, the coming and going of mythological characters, the migrations of certain important birds, fish or mammals needed for food, or based upon important weather events such as a hurricane season, tornado season, pack ice season or a wildfire season.