Spring starts today (22) in the Southern Hemisphere, at 10:04 pm, and thus we leave winter behind. This is the moment that marks the end of a period of drought in the central region of Brazil, which begins to experience more rainy and humid days. The other regions are also affected by the beginning of the transport of moisture coming from the Amazon, explaining the incidence of rains in the Southeast, Midwest and North of the country.
But what are the seasons and how do they occur? The explanation comes from the tilt of the Earth in relation to the sun. The Earth makes two movements, rotation and translation. The rotation is a movement of the planet around its own axis and lasts for 24 hours. The translation is a movement around the sun and lasts 365 days.
These movements of the planet cause phenomena such as longer and shorter days, in addition to the change of the seasons: spring, summer, autumn and winter. But this is only due to the tilted position of the Earth. If it weren’t tilted on its axis, there would be no change of seasons and every day would have 12 hours of light and 12 hours of darkness.
And it is the rotation and the translation that allow the calculation of the exact day and time for the change of seasons.
The seasons vary according to the inclination of the sun’s rays and the position of the Earth in relation to the sun. When the movement of the Earth positions the South Pole towards the sun, the Southern Hemisphere (where South America and Australia are, for example), gets warmer, bringing summer. At the same time, it is winter in the Northern Hemisphere (where the United States and Europe are, for example). Six months later, the position of the poles is reversed and it is the turn of the North Pole to receive more light and heat, bringing summer to the countries further north. At this time, the Southern Hemisphere is experiencing winter.
Spring, which begins today, marks the end of winter, being the transition season until summer, scheduled to begin in the Southern Hemisphere on December 21. The start of spring date is when we have the same amount of sunlight in both hemispheres, Southern and Northern, and day and night are the same length.
Traditionally, spring brings back longer and warmer days, but not as hot as summer. It is usually a time of moderate temperature. It is during this period that animals reproduce and some insects fly in search of nectar from flowers.
This year, however, the beginning of spring will not be so pleasant. According to the National Institute of Meteorology (Inmet), a cold front is arriving in the southern region of the country and in the states of Mato Grosso do Sul and São Paulo, which reduces temperatures and increases the amount of rain.
As explained by Heráclio Mendes, meteorologist at Inmet, the weekend arrives very cold in the south of the country. “With the advance of this cold front between Thursday and Friday, the chance of a much lower temperature in Rio Grande do Sul, Santa Catarina, even with a chance of frost formation,” he told National Radio. He added, however, that this scenario is changing as summer approaches, in the second half of December.
In summer, the temperature is higher and the days are longer, especially in countries further away from the equator. The trees are more fruitful and there is an incidence of rain due to water vaporization. Therefore, sometimes the sky is cloudy, thanks to the accumulation of water from rivers and seas transported to the atmosphere in the form of steam. In the Southern Hemisphere, summer starts on December 21 and ends on March 21.
Autumn marks the harvest season. The days get shorter and cooler, and the fruits and leaves are ripe and start to fall off. A typical autumn landscape features trees with yellowish or reddish leaves, and the ground is also full of them. In the Southern Hemisphere, autumn begins around March 21st and runs until June 21st.
Finally, winter is the coldest period, where the hemisphere has less direct contact with the sun. The days are much shorter, especially in countries further away from the equator, and the nights are colder. In southern Brazil, snow and frost are not uncommon. It is during this season that some animals go into hibernation and retreat. In the Southern Hemisphere, winter starts around June 21st and ends around September 21st.
Solstice and Equinox
Other phenomena related to the movements of the Earth are the solstice and the equinox. The summer solstice represents a day longer than the others. This is thanks to the positioning of one of the hemispheres, more towards the Sun. That way, it stays brighter and longer, making this day reach its peak duration throughout the year.
While one hemisphere experiences the summer solstice, the other experiences the winter solstice, when sunlight is at the farthest point of the year. There is also the equinox, the mid-point of the two solstices. At the equinox, the two hemispheres of the Earth are equally illuminated. It marks the official beginning of autumn in one hemisphere and spring in another.
Translated to english by RJ983
From Brazil, by EBC News