A phenomenon occurs when one of the hemispheres is tilted at the angle at which it receives the most sunlight possible.
THE summer officially began at 12:03 p.m. (Brasilia time) this Sunday 21. This date marks the summer solstice in the southern hemisphere, an astronomical phenomenon that makes it the day with the greatest number of hours of light throughout the year.
The different seasons occur due to the tilt of the axis of rotation of the Earth with respect to its orbital plane and the translational movement of the planet around the Sun. The summer solstice occurs when one of the hemispheres is tilted to receive the greatest possible incidence of direct sunlight.
At the same time, the winter solstice takes place in the northern hemisphere, when the longest night of the year is recorded. In June, the situation is reversed: the southern hemisphere enters winter, while the northern hemisphere enters summer.
In addition to the solstices, there are equinoxeswhich take place in spring and autumn. They mark when both hemispheres receive the same amount of sunlight, giving day and night a similar duration.
What happens in summer?
According to Josina Nascimento, astronomer at the National Observatory (ON), an institution linked to the Ministry of Science, Technology and Innovation (MCTI), summer is the hottest season of the year precisely due to the inclination of approximately 23 degrees of the Earth’s axis in relation to its orbital plane. This angle causes the sun’s rays to hit one hemisphere at a time more directly.
When it’s summer in the southern hemisphere, the sun’s rays fall more intensely on this region of the planet, leading to longer days and higher temperatures.
The effects of the seasons are greater in places far from the Earth’s equator. “In regions close to the equator, the length of days varies little throughout the year. This difference gradually increases towards the poles, where contrasts are greatest,” explains Nascimento.
Weather forecast for the next few days
With the arrival of summer this Sunday, Sao Paulo there are expected to be some warm days in the coming weeks and could break the year’s temperature record on Christmas Eve. According to Climatempo, the next few days should also be marked by less rain and dry weather in the capital São Paulo.
Data from the National Institute of Meteorology indicates that the highest temperature recorded in São Paulo in 2025 was 35.1°C on October 6. For December 24, the temperature is expected to approach 35°C, which could equal or even exceed the record for the year.
The heat must be constant in much of Brazil. This week, Rio de Janeiro could record up to 38°C and Belo Horizonte and Vitória are expected to reach highs between 32°C and 34°C, with little rain. Hot temperatures are also expected to reach the Southern region and the interior of the Northeast, with maximum temperatures near 35°C. In the North, maximum temperatures approach 32°C.
Summer lasts until 11:45 a.m. on March 21, 2026 and will be marked by the South Atlantic Subtropical Anticyclone (ASAS), a high atmospheric pressure system that acts on the South Atlantic Ocean and inhibits cloud formation. The weather phenomenon is expected to act as an atmospheric blockage, suppressing some cold fronts that cross Brazil.
Climatempo predicts that precipitation in the summers of 2025 and 2026 will be slightly below the season average across most of the country. The greatest deficiency is expected to be on the northern coast of Brazil, between the coasts of Pará and Ceará, and in the interior areas of Maranhão and Piauí.
The phenomenon La Nina it is not expected to be the main climatic driver this summer, due to its low intensity and short duration. The phenomenon is expected to last until mid-January 2026 and its influence on this season’s weather conditions tends to be limited.
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