Examples / Earth science
Why do we have seasons?
Drawn and explained by Sketchwise from this one question.
The explanation, step by step
1. The changing year
Every year the trees around us turn from green, to gold, to bare, and back again. So why does Earth have seasons at all? Let's fly up into space and find out!
2. A tilted Earth
Here is our Earth, spinning on an invisible line through its poles called its axis. But that axis is not straight up: it leans over by about twenty-three and a half degrees. I lean the same way all year long, like a spinning top that never straightens up.
3. Around the Sun
Each year Earth travels all the way around the Sun on a nearly circular path. Many people think summer comes from being closer to the Sun, but Earth is actually closest in January! Watch the tilt: it always points the same way, so in June the north leans toward the Sun. Half a year later, on the far side, that same lean points the north away.
4. Steep light, slanting light
The lean matters because of the angle at which sunlight strikes the ground. When light hits straight down, all its energy is packed into a small, hot spot. Coming in at a slant, the same light spreads thin over more ground, and warms much less.
5. Summer here, winter there
Now let's look at Earth from the Sun's point of view, here in June. The north leans in, so it gets steep sunlight and long days: that's summer. Meanwhile my southern half leans away and gets slanting light, so it's winter down there. Six months later the lean points the other way, and the two halves swap seasons.
6. It's the tilt
So seasons come from Earth's tilt, not from how far we are from the Sun. Lean toward the Sun for summer, away for winter, round and round every year!
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