On this episode of Our Island Universe: Do you know why the seasons change?
Shanil Virani, Director of the John C. Wells Planetarium in Harrisonburg, VA.
Follow on Twitter as shanilv
Transcript:
What is the cause of the seasons? Winter, Spring, Summer, Fall repeat year after year but why we do we have them? Consider that this is a topic that is taught in elementary, middle and high school yet survey after survey has revealed that the cause of the seasons is one of the biggest misconceptions in all of science.
What is the path the Earth takes in its year-long journey around the Sun? It is not a perfect circle, like a hula hoop, instead its an ellipse with a changing Earth-Sun distance. In fact, this is the most popular but WRONG answer to our question! The Earth-Sun distance does change over the course of the year but the effect is very small — about 2%! In fact, the Earth is closest to the Sun in early January and we’re farthest from the Sun in early July! That is the middle of winter and summer, respectively, in the northern hemisphere! Let’s consider two observations that we’ve all witnessed. In the summertime, days are long and nights are short. The Sun is also high in the sky! These two effects gives us warmth, and hence summer. In the Winter, the days are short and the nights are long. The Sun is also LOW in the sky. These two effects give us cool, and hence winter. It is the Earth’s tilt that cause these effects!
The cause of our seasons is due to the fact that the Earth’s rotation axis is tilted by 23.5 degrees. And this explains the observations that we just made and that our Ancestors decoded thousands of years ago.