Seasons on Earth: Causes, Types, Classification, Effect & Diagram

Our Earth takes 365.24 days to complete one full revolution around the Sun. We refer to this duration of one revolution as a “year”.  This year is further distributed into various seasons. From specific climatic conditions and time periods to daylight duration and ecology, every season is demarcated by its own unique set of features. The extent and impact of these seasons also depend on the location of a place on Earth. This article gives you an insight into the seasons of the year, their features, reasons behind the occurrence of different seasons, and the key differences between season and weather-climate.

What is a Season?

A season refers to a division of the year based on ecological transitions, weather changes, amount of daylight, and the time duration. Different climatic regions have different criteria for classifying the seasons. The impact of seasons also varies from region to region.

Classification of the Seasons

Seasons are broadly classified on the basis of climatic region, ecology, and the amount of daylight received during the period.

1. Temperate & Sub-Polar Region: Most of the temperate and sub-polar regions follow the four-season model as per the Gregorian calendar. This classification is the most common of all the classifications and it is mainly followed in the temperate and sub-polar regions. In sequence, these seasons are spring, summer, autumn, and winter. Autumn is also known as Fall in some areas.
2. Temperate Region (Six Season Cycle):  Apart from the general four-season classification, there is a six-season model that is commonly used by ecologists. The six seasons as per this model are – prevernal, vernal, estival, serotinal, autumnal, and hibernal. The time period for each season may vary depending upon the climatic condition of a region. At times, the seasons also make a shift from one year to the next year.
3. Tropical Region: In hot tropical climatic regions, seasons are mainly divided into – rainy/wet season and dry seasons. The rainy season is also referred to as monsoon in some areas of the Indian subcontinent.
4. Polar Regions: Based on the duration of daylight received in the poles, the seasons are divided as polar day and polar night.

Astronomical Seasons

It is the date of equinox and solstice that marks the duration of astronomical seasons.  Spring and autumn equinoxes mark the beginning of the spring and autumn seasons. Similarly, summer and winter solstices mark the beginning of the summer and winter seasons. The length of astronomical seasons in a year usually varies. This is due to the change in timings of equinoxes and solstices every year.

Cause of Seasons on Earth

There are two main causes of seasons on Earth:

• The revolution of Earth on its orbit
• The axial tilt of Earth relative to the ecliptic plane

Seasons in Northern & Southern Hemisphere

Northern and Southern Hemisphere experience exact opposite seasons at any given time of a year. When Northern Hemisphere experiences summer, it’s winter in the Southern Hemisphere. Similarly, when the Southern Hemisphere experiences spring season, it’s autumn or fall for the Northern hemisphere. It is mainly due to the axial tilt of Earth that when one hemisphere faces the direct sun, the other hemisphere moves away from the direct sunlight range.

Month Range & Seasons in Both the Hemispheres

Range of Months	Season in the Northern Hemisphere	Season in the Southern Hemisphere
June – August	Summer	Winter
September – November	Autumn/Fall	Spring