Why do we have seasons?
In summer we put on T-shirts and go to the beach; in winter, coats and scarves. Why does the weather change through the year? Many people think the Earth is closer to the Sun in summer, but that is not true. The secret is the tilt of our planet.
A tilted Earth
The Earth spins like a top, and one turn takes a day. But its axis is not upright: it is tilted about 23 and a half degrees. While spinning, it also travels around the Sun once a year, and that tilt always points toward the same side of space.
Direct light and long days
When your half of the Earth is tilted toward the Sun, its rays arrive more directly and heat more. Days are also longer and nights shorter, so there are more hours to warm the ground and the air. That is summer. Six months later, your half is tilted the other way: the rays arrive at a lower angle, days are short and it is colder. That is winter.
Spring and autumn
In between come spring and autumn, when the Earth is tilted neither toward the Sun nor away from it. Days and nights last almost the same and temperatures are mild. In spring plants bloom; in autumn, many trees lose their leaves.
The world upside down
Because the tilt affects each half of the planet in the opposite way, the seasons are opposite: when it is summer in Spain, it is winter in Argentina or Chile, and vice versa. Near the equator there are hardly any marked seasons, while near the poles there are periods of very long days and others of very long nights.
Experiment: the flashlight
You need a flashlight and a ball. In a dark room, shine the light straight at the ball: you will see a small, bright circle of light. Now tilt the flashlight: the light spreads over a bigger area and looks weaker. Something similar happens with the Sun: direct rays concentrate more heat, while slanted rays spread it out.
What about the distance to the Sun?
The distance to the Sun does change slightly during the year, but the Earth is actually closest to it in January, in the middle of winter in the northern hemisphere! So distance does not explain the seasons.
💡 When it is summer in Spain, it is winter in Argentina.
