The Earth has a tilt
Summer is warmer mainly because your half of Earth gets more direct sunlight and longer days. This happens because Earth leans as it travels around the Sun.
Picture a spinning globe. An imaginary line runs through its North and South Poles. That line is called its axis. Earth spins around this line, which is tilted rather than upright compared with its path around the Sun.
At one part of the year, the northern half of Earth leans towards the Sun. About six months later, the southern half does. This changing view of the Sun gives us our seasons.
What does “hemisphere” mean?
A hemisphere is half of a sphere. Here, it means half of Earth.
The Northern Hemisphere is the half north of the equator, the imaginary line around Earth’s middle. The Southern Hemisphere is the half south of it.
When the northern half leans towards the Sun, the southern half leans away. That is why their summer and winter happen at opposite times.
Two things help summer feel warmer
- Sunlight hits more directly. Picture a torch shining straight down on a table. Its light makes a small, bright patch. Tilt the torch and the light spreads over a larger patch. Sunlight arriving at a low angle is spread out too.
- The days are longer. There are more hours of daylight for the ground to warm up.
These changes help explain summer warmth. A particular summer day can still be cold or rainy: daily weather can vary.
One planet, opposite seasons
| Northern half | Southern half |
|---|---|
| Summer: longer days, more direct sunlight | Winter: shorter days, less direct sunlight |
| Winter: shorter days, less direct sunlight | Summer: longer days, more direct sunlight |
Is summer just when Earth is closer to the Sun?
No. Earth’s distance from the Sun changes a little during the year, but it does not explain why one half of Earth has summer while the other has winter.
The tilt explains that difference. It changes the sunlight reaching each half through the year.
Look for a small clue outdoors
Over a few weeks, notice whether it gets dark earlier or later. Those changing daylight hours are one clue to the seasonal pattern.
You do not need to look at the Sun. Simply noticing when daylight ends is enough.