The Earth’s revolution not only affects but actually causes the temperature conditions that give us spring, summer, fall and winter seasons. Which season it is depends on whether you live in the Northern or Southern Hemisphere because the Earth’s axis tilts toward one of the two as it moves around the sun. The seasons are always opposite in each hemisphere. This rotational process causes the sun to be higher in the sky in the winter and lower in the summer.

The Earth orbits the sun once a year, causing its two hemispheres to shift positions, either pointing toward the sun or away from it. The hemisphere pointing toward the sun is in summer and the hemisphere pointing away from it is in winter.

The Earth’s axis, the imaginary line around which the planet spins, is tilted. This causes the planet to lean away from the sun, receiving only indirect solar energy in the winter, and direct solar energy in the summer. Temperatures increase in the summer because the sun’s energy is more concentrated.

Because the Earth orbits the sun over 12 months, countries in the Southern Hemisphere, which include Australia and parts of Africa and South America, enjoy their summer during North America's and Europe’s winter months. However, countries closer to the equator are hotter throughout the year.

Gradual shifts in the Earth’s tilt can cause climate changes. More tilt means more severe seasons, meaning that it is hotter in the summer and colder in the winter. Less tilt results in moderate seasons: warmer winters and cooler summers. However, these changes occur over a long period as the Earth's tilt shifts from 22 to 25 degrees over a cycle of about 41,000 years.