Chapter 2: Why Do We Have Seasons?

A gentle note: “summer means the Earth is nearer the Sun”

It seems very reasonable that summer is hot because the Earth moves closer to the Sun. But if that were true, the whole Earth would have summer at once — and it does not. When the north has summer, the south has winter. The real cause is the Earth's lean, which changes how directly the Sun's light falls on each part.

Story Time — The Umbrella and the Torch

Aarav · Delhi

Aarav, who had learned about the sunrise on his terrace, now had a harder question. Delhi's summer was so fierce that the roads seemed to shimmer, yet in winter he needed two blankets. “Why does the same Sun feel so different?” he asked his science teacher.

His teacher brought a torch and a small globe to class. She tilted the globe to one side, the way the real Earth leans. “Watch,” she said, shining the torch straight ahead. “When the top half of the Earth leans towards the Sun, the light falls straight and strong upon it. That is summer.”

Then she carried the globe to the other side of the torch, keeping the same lean. Now the top half leaned away, and the light struck it at a slant. “The same light,” she said, “but spread thin and weak. That is winter.” Aarav frowned. “So the Earth did not move closer or farther. It only leaned?”

“Exactly,” she said. “The seasons are not about distance from the Sun. They are about the lean of the Earth, and whether your part is leaning towards the Sun or away from it.” Aarav thought about the fierce summer sun striking Delhi straight from overhead, and the weak winter sun sitting low in the sky.

“That is why the winter Sun feels gentle,” he said slowly, “and the summer Sun feels strong.” His teacher nodded. “The very same Sun — only the angle has changed.” Aarav never again complained about the cold without remembering the tilted globe and the patient torch.

Story Time — Two Letters, Two Seasons

Priya · Madurai, Tamil Nadu

Priya had a pen-friend named Emily who lived in Australia, far to the south of the Earth. They wrote letters to each other every month. One December, Priya wrote about her cool, pleasant winter and the warm shawls her family wore in the mornings.

Emily wrote back something strange: “It is the middle of summer here! We went swimming at the beach for the holidays.” Priya read it twice. “How can it be summer there and winter here, in the same month?” she wondered aloud.

Her elder brother explained. “Remember, the Earth leans to one side. In December, the southern half of the Earth — where Australia is — leans towards the Sun, so they have summer. Our northern half leans away, so we have winter.”

“So we are on the same Earth, the same distance from the Sun,” Priya said, “but different seasons, because of the lean?” “Yes,” her brother said. “When your half leans towards the Sun, you get summer. Six months later, as the Earth moves around the Sun, it will be the other way around.”

Priya wrote back to Emily: “We are like two ends of a see-saw. When you go up into summer, I come down into winter — and then we swap.” Emily wrote that it was the best explanation of seasons she had ever read.