Why Does the Weather Get Hot in Summer?

According to Saed News and citing Sina Press:

In the Northern Hemisphere, the average annual peak position of the Sun occurs on 31 Khordad at 17:56 local time in Iran. From an astronomical perspective, the summer solstice occurs once every four years at the end of Khordad and three times at the beginning of Tir. Each year, one of these two days marks the longest day of the year. However, in the customary and calendar-based view, the summer solstice is considered to fall on the first day of Tir.

On the day of the summer solstice, the Sun reaches its highest apparent altitude (about 23.5 degrees) relative to the North Pole. It is also directly overhead at the Tropic of Cancer in the Northern Hemisphere. At this moment, at local noon, the Sun reaches its maximum elevation above the southern horizon for an observer. It rises from the northernmost point of the eastern horizon and sets at the northernmost point of the western horizon, marking the beginning of summer in the Northern Hemisphere. People living on the Tropic of Cancer can see the Sun directly overhead at noon.

At the beginning of spring, day and night are nearly equal in length. Gradually, daylight increases, reaching its maximum during the summer solstice, the longest day of the year. As autumn approaches, days gradually become shorter again until day and night are equal once more at the start of autumn.

In the Southern Hemisphere, the situation is exactly the opposite, with seasons reversed. While the Northern Hemisphere experiences the summer solstice and the beginning of summer, the Southern Hemisphere experiences the winter solstice and the beginning of winter.

Exact Timing of Iran’s Summer Solstice

According to Massoud Atighi, director of the Amateur Astronomy Association of Iran, the Sun moves along the ecliptic (the apparent path in the sky known as the zodiac) during its annual motion. Meanwhile, the extension of Earth’s equator onto the celestial sphere forms a great circle dividing the sky into northern and southern hemispheres, called the celestial equator.

Because the celestial equator and the ecliptic are inclined at an angle of 23.5 degrees, they intersect at two points known as the equinoxes (vernal and autumnal). The points between the equinoxes are called the solstices, one being the summer solstice and the other the winter solstice. At the solstice points, the Sun reaches its maximum angular distance from the celestial equator in its apparent motion.

At the summer solstice, which occurs on Thursday, 31 Khordad at 14:37 Iran time, the Sun reaches the solstice point. At this moment, summer begins in the Northern Hemisphere, including Iran, while winter simultaneously begins in the Southern Hemisphere.

Why Is Summer Hot?

Atighi explains that summer heat is not caused by the Earth being closer to the Sun. Instead, it is due to the Sun’s more direct (nearly vertical) angle of radiation during this season in the Northern Hemisphere.

Some people mistakenly believe that summer is hotter because Earth moves closer to the Sun. However, in reality, during the Northern Hemisphere’s summer, Earth is actually about 5 million kilometers farther from the Sun. Given the average distance of about 150 million kilometers, this difference has little effect on temperature.

The true reason for seasonal temperature changes is the angle of sunlight: when sunlight is more direct, it concentrates energy over a smaller surface area, resulting in higher temperatures.