What causes the seasons?
Claud H. Sandberg Lacy, professor of physics, replies:
The rotational axis of the earth is tilted by 23.5 degrees from its orbital pole. Also, the direction of the earth’s rotational axis does not change as the earth orbits the sun once a year. This fixed orientation of the earth’s axis causes the Northern and Southern hemispheres of the earth to face the sun most directly at opposite times during the year due to the earth’s orbital motion around the sun.
When a hemisphere of the earth is facing the sun, it is more strongly heated by the sun’s light during the day, so that hemisphere’s temperature is higher and it is summer there. The opposite effect occurs in the hemisphere turned away from the sun, so when it’s summer in the Northern Hemisphere, it’s winter in the Southern Hemisphere.