Question

Question #3376b

Answer 1

Due to tilt of the earth's axis making different parts of earth receiving different levels of sunshine during revolution of the earth.

Explanation:

The earth is tilted slightly on its axis (imaginary line passing from top to bottom of the earth). This makes a part of the earth lean towards the sun. During earth's revolution, the northern hemisphere faces the sun for 1/2 of the year and southern hemisphere for next half of the year.

The side facing the sun gets direct sun rays and gets hot (summer) and the side away from the sun becomes cooler (winter). Thus, the seasons are always opposite in northern and southern hemisphere.

Please see this link for a pictorial explanation:
https://www.windows2universe.org/earth/climate/cli_seasons.html