What Makes The Seasons Change?

9/18/2014 (Permalink)

Many people look forward to changing seasons: the brilliant colors of fall, gentle snows of winter, fragrant blossoms of spring and sunbathing days of summer. The rhythm of winter to summer and back again is so predictable that few stop to remember why this happens.

While the Earth’s orbit around the sun is a key player in making sure the seasons change, the most important aspect is the tilt of our planet's axis of rotation, which comes to about 23.5 degrees. The tilt is always there, but as Earth makes its laps around the sun, the amount of daylight we receive varies.

So why is the Earth tilted in the first place? Most of our planet's landmass and ice buildup is in the Northern Hemisphere, making it a bit top-heavy. If it weren't for the tilt, our seasons would have very little variation, making fall, winter, spring and summer somewhat one-note.

In a Northern Hemisphere summer, the planet is oriented toward the sun and receives enough solar radiation to thaw out and warm things up. While this is happening, the Southern Hemisphere experiences less solar penetration and colder temperatures, thus inaugurating its winter. Six months later, thanks to the Earth's orbit, the opposite is true. In between these two dominant seasons come spring and autumn, which help serve as a healthy transitional period.

3 quick facts about the changing seasons:

• Other planets in our solar system also tilt at various degrees. Uranus rotates almost sideways at 97 degrees and has extreme seasons. The axial tilt on Venus is 177.3 degrees, causing very little variation to the seasons.

• Earthquakes can shift the Earth's axis, but only by an infinitesimal proportion.

• Earth is decreasing in obliquity, or tilt. An increase in tilt can lead to ice-age conditions, while a decrease in tilt can warm the Earth's surface.