* Summer solstice: This occurs around June 21st in the Northern Hemisphere and December 21st in the Southern Hemisphere. The North Pole is tilted towards the Sun, and the angle between the rotation axis and the Sun is at its maximum for that hemisphere.
* Winter solstice: This occurs around December 21st in the Northern Hemisphere and June 21st in the Southern Hemisphere. The North Pole is tilted away from the Sun, and the angle between the rotation axis and the Sun is at its maximum for that hemisphere.
This tilt of the Earth's axis is the primary reason we have seasons. When a hemisphere is tilted towards the Sun, it receives more direct sunlight and experiences longer days, leading to summer. When a hemisphere is tilted away from the Sun, it receives less direct sunlight and experiences shorter days, leading to winter.
