What causes the seasons?

Our fundraising campaign to bring a planetarium to the western GTA is running on Indiegogo. We have posted a video about Eddie who is working on a Science Fair project to explain why we have seasons.  


There is a misconception out there that the distance of the Earth to the Sun results in our seasons. This is not true. The Earth's distance does vary during the year.  The Earth is actually a little closer to the Sun in January than in July - by about 3%. This is too little to really affect our weather. 

The major cause of our seasons is due to the tilt of the Earth's axis with respect to its orbit. The tilt is 23.5 degrees from vertical. As a result, the northern hemisphere is tilted towards the Sun in the summer months - the Sun appears higher in the sky, the days are longer and the heat from the Sun is more concentrated in the north. Six months later, the northern hemisphere is tilted away from the Sun. The Sun is lower in the sky, the days are shorter and less heat is concentrated in the north.

The seasons in the southern hemisphere are the opposite - they have summer at Christmas and winter in June and July. As for the equator - it is pretty well hot all the time!

 Credit: http://www.lpl.arizona.edu/

Credit: http://www.lpl.arizona.edu/

How would a planetarium have helped Eddie? FIrst, he would have been able to discuss the problem with experts. Second, a planetarium can show the changing positions and altitude of the Sun in the sky - the reason we have seasons.  

Below we have posted a good video which helps to explain why we have seasons - thanks to TED ED and Rebecca Kaplan for this. 

View full lesson: http://ed.ted.com/lessons/reasons-for-the-seasons-rebecca-kaplan Why do some regions experience full-time heat while others are reckoning with frigid temperatures and snow? And why are the seasons reversed in the two hemispheres? Rebecca Kaplan explains how the shape of the Earth's orbit around the Sun and the Earth's tilt on its axis affect the amount of sunlight each region receives.