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.

Lesson by Rebecca Kaplan, animation by Marc Christoforidis.