The Misleading Orbit
Many of us learn that the Earth’s orbit around the sun is not a perfect circle, but an ellipse. This is true. This elliptical path means that our distance from the sun changes throughout the year. There is a point when we are closest, called perihelion,
and a point when we are farthest, known as aphelion. Logically, one might assume our seasons are tied to this distance—closer for summer, farther for winter. But reality is exactly the opposite for the Northern Hemisphere. Earth reaches perihelion (closest point) in early January, during our winter. It reaches aphelion (farthest point) in early July, squarely in the middle of our summer. In 2026, for instance, aphelion occurs on July 6, when Earth will be over 152 million kilometres from the sun. This simple fact proves that distance cannot be the main reason for our seasons.
The Real Culprit: Earth's Tilt
The true cause of the seasons is the tilt of the Earth’s axis. Our planet doesn't spin straight up and down as it orbits the sun; instead, it is tilted by about 23.5 degrees. Think of it like a spinning top that is leaning to one side. Crucially, this tilt always points in the same direction in space as Earth makes its year-long journey. This means that for part of the year, the Northern Hemisphere (where India is located) is tilted towards the sun, and for the other part, it is tilted away from the sun. This tilt, not our orbital distance, is the main event. It’s a cosmic lean that dictates everything from the summer heat to the winter chill.
Direct vs. Indirect Sunlight
So, why does this tilt matter so much? It all comes down to the angle at which the sun's rays hit the planet. When the Northern Hemisphere is tilted towards the sun, as it is in June and July, we receive sunlight more directly. Imagine shining a torch directly onto a piece of paper—the light is concentrated in a small, bright, and intense circle. This is summer. The direct rays deliver a powerful dose of energy, which heats the land and atmosphere more efficiently. Conversely, when our hemisphere is tilted away from the sun, as in December and January, the same rays strike us at a much lower angle. Like shining that same torch at a slant, the light is spread out over a much larger area. The energy is less concentrated, more diffuse, and therefore weaker, leading to the colder temperatures of winter. This is also why days are longer in the summer and shorter in the winter.
A Tale of Two Hemispheres
The most compelling evidence for the role of axial tilt is that the seasons are opposite in the Northern and Southern Hemispheres. When we in India are enjoying (or enduring) our summer, countries like Australia and South Africa are experiencing winter. That's because when our hemisphere is tilted towards the sun, theirs is tilted away. If seasons were caused by our distance from the sun, the entire planet would experience summer and winter at the same time. The fact that they are reversed is definitive proof that it is the direction of the tilt relative to the sun that matters. The slight change in distance from the sun over the year does have a small effect on climate, accounting for about a 7% variation in solar energy received, but this is a minor factor completely overshadowed by the effect of the axial tilt.
