Seasons on Earth are beautiful. Spring heralds in new life for animals and plants, summer has plenty of warm sunshine and blue skies, fall is decorated with leaves changing colors, and winter brings glistening snow and ice. These changes are caused by the fact that Earth is not sitting straight up and down with respect to its orbit; it is tilted on its axis by 23.5 degrees. Not only does this explain why we get seasons, but also why the Northern and Southern hemisphere do not experience the same season at the same time.
Earth’s orbit around the sun is not perfectly round. It is elliptical and the sun isn’t even directly in the middle. It is easiest to talk about how seasons are made in terms of our closest approach with the sun (Perihelion) and farthest approach (Aphelion). At Aphelion, the North Pole is pointed more toward the sun while the South Pole is pointed away. This allows the North Pole to receive a greater amount of the sun’s light and heat, causing summer in the Northern Hemisphere and winter in the South. Alternatively, the opposite is true at Perihelion. In between these points are the transition seasons of spring and autumn.
EUMETSAT, a meteorological satellite agency based of Europe, maintained a fixed position on Africa between 2010 and 2011. All of the images were then put together into a time lapse video to see what the seasons look like from space. It is easy to see how the shadow changes depending on the Earth’s position with the video starting near Perihelion.