category : Biodiversity and nature preservation
Reasons for the seasons
The earth revolves around its axis. The Earth’s axis is a line of thought that passes through the centre of the Earth and crosses the Earth’s surface at two points: the North and South Poles. The seasons occur in a strictly defined and unchanging sequence due to the inclination of the earth’s axis (23.5 degrees). When the axis is inclined towards the Sun, the Northern Hemisphere receives more light and heat and it is summer there. When the North Pole is tilted towards the sun in Bulgaria and Serbia is summer. More sunlight and more solar energy reach us in one hour. In winter, the Earth is inclined to the Sun from the South Pole and therefore we receive less light and heat.
In fact, even during its orbit around the Sun, the Earth’s axis does not change its inclination. If the earth’s axis was upright, we wouldn’t have seasons.
Due to the tilt of the Earth’s axis, in spring and autumn the Earth is tilted in such a way that the Sun shines equally on the North and South Poles. Autumn begins in September and ends in November. Spring begins in March and ends in May. Summer begins in June and ends in August, and winter – in December to February.
That is why they exist – the autumn equinox, the vernal equinox, and the winter and summer solstices.
Continents and countries with fewer seasons
For the same reason, some countries that are closer to the equator and where the slope of the earth’s axis is less pronounced have two seasons or only one – summer, and others that are closer to the poles one season – winter.
In winter it is dark even during the day. The weather is usually cold and it often snows. Some animals hibernate or sleep for a long time. Many birds have moved to warmer places. Some plants die and others stop growing.
When spring comes, temperatures get higher. Plants and trees produce new leaves and flowers. The birds return from their winter homes and the animals wake up from hibernation.
In summer the temperatures reach their highest levels. The sun shines late and is warm even at night. There are more hours of daylight and the sun is stronger. This extra sunlight helps the plants grow.
Temperatures fall again with the beginning of autumn. Some trees and plants lose their leaves. Furry animals have thicker hair to keep warm in the coming winter. Many birds travel to warmer places.