Earth rotates on its axis about once a day, moving places into and out of sunlight. It revolves around the Sun about once a year. Its axis is tilted relative to its orbit. When the Southern Hemisphere tilts toward the Sun, it generally has longer daylight and more direct sunlight, producing summer conditions.
The hemispheres have opposite seasons because they receive different sunlight angles and day lengths at the same time. Distance from the Sun is not the main cause. Around an equinox, day and night are approximately equal. Around a solstice, day-length contrast is greatest. Always check the stated hemisphere: December summer suits Adelaide but not London.
Example 1
Why can Adelaide have summer while London has winter?
Earth’s tilted axis gives the Southern Hemisphere longer days and more direct sunlight while the Northern Hemisphere receives the opposite pattern.
Example 2
Which motion causes one place to pass from day to night?
Earth’s rotation moves that place from the sunlit side to the side facing away.
Watch out: Axial tilt changes sunlight angle and day length. Opposite seasons in the two hemispheres rule out distance as the main cause.