Fundamentals of Seasons
Earth’s Axial Tilt and Orbit
The Earth’s axial tilt, which is about 23.5 degrees, plays a crucial role in the formation of seasons.
When Earth orbits the Sun, this tilt causes different hemispheres to receive varying amounts of direct sunlight throughout the year, resulting in the annual temperature and climate changes we know as seasons.
The northern and southern hemispheres experience opposite seasons due to their contrasting positions relative to the Sun during Earth’s orbit.
Solstices and Equinoxes
Solstices and equinoxes mark the beginning of our astronomical seasons.
During a solstice, either the North Pole or the South Pole is tilted most towards or away from the Sun.
The summer solstice occurs around June 21, when the North Pole is tilted towards the Sun, resulting in the longest day of the year in the Northern Hemisphere.
Conversely, the winter solstice takes place around December 21, when the North Pole is tilted away from the Sun, leading to the shortest day in the Northern Hemisphere.
Equinoxes happen twice a year, marking the point when the Earth’s equator aligns with the center of the Sun.
During these times, day and night are approximately equal in length all around the world.
The vernal equinox occurs around March 20 and signifies the beginning of spring in the Northern Hemisphere.
Meanwhile, the autumnal equinox takes place around September 22, marking the start of fall in the Northern Hemisphere.
Although our understanding of seasons is largely based on astronomical events, the way we define them in daily life often aligns with the Gregorian calendar.
This widely-used calendar system organizes seasons into roughly three-month periods, with the December solstice, March equinox, June solstice, and September equinox serving as their starting points.
Seasonal Impact on Earth and Life
Climatic Variations
Seasons are caused by Earth’s tilted axis, which affects the amount of direct sunlight received by different parts of the planet throughout the year1.
This leads to variations in temperature, rainfall, and weather conditions, depending on the climate of a region.
For example, countries in South Asia typically experience wet and dry seasons, while in the United States, regions such as the Midwest and Eastern Time Zone have more distinct meteorological seasons.
Finland and Sweden, found closer to the polar regions, can experience extreme darkness in the winter months and abundant sunlight during the summer.
Flora and Fauna
Changes in vegetation and leaves falling correlate with seasonal transitions.
The growth of plants and flowers is influenced by light, temperature, and water availability.
In spring, many plants come out of dormancy and begin to grow, while in autumn, they prepare for the colder months.
Animals also adapt to seasonal variations.
For example, some birds migrate to warmer locations, and mammals like bears hibernate during the winter months.
In colder regions, animals like the Arctic fox may grow thicker fur for insulation.
Human Activities and Culture
Seasons often impact human activities and culture, with diverse observances and festivities depending on the region and climate.
For example, in Latin America, many countries celebrate Day of the Dead in autumn, while in India, the Hindu calendar marks six seasons, known as ritu, and various cultural festivals are associated with these seasons.
In Australia and New Zealand, the summer season coincides with Christmas, leading to unique celebrations.
Similarly, in Argentina, summer occurs during what is traditionally the hurricane season in other parts of the world.
Seasonal variability can also affect agriculture, tourism, outdoor sports, and many other activities that depend on weather conditions.
In colder climates such as Alaska, winter provides opportunities for ice fishing and skiing, while summertime in the tropics often brings rain and humidity.