Earth is tilted
The axis is inclined relative to the plane of its orbit.
Sun angle changes
A hemisphere tilted toward the Sun receives more direct sunlight.
Day length changes too
Longer daylight adds more solar energy during that hemisphere's summer.
The hemispheres have opposite seasons
When the north is tilted toward the Sun, the south is tilted away.
Source trail: NASA: star basics
This page explains scientific concepts for general learning. It does not replace laboratory safety procedures, professional engineering guidance, or individualized medical advice.