One persistent misconception in astronomy is the answer to the question of what is the cause of the seasons. The prevailing idea amongst the public is that the Earth is farther away from the Sun in winter and closer to the Sun in summer.
Let’s see where this idea takes us. If so, then one will want to ask the following question: when it is winter in the northern hemisphere, which season is it in the southern hemisphere? We all know that when it is winter in Arizona and we ring up our best friend in Sydney, Australia, she will say it is summer. So, the seasons are not caused by the Earth’s orbit.
In fact, it is actually winter in the northern hemisphere when the Earth is closest to the Sun.
The second idea brought up in classes is that the Earth is tilted. The tilt has an effect on the quality or the intensity of the sunlight. In winter the Sun is farther from being overhead. This larger angle of incidence of sunlight results in cooler, shorter days. By contrast, in summer the Sun closest to being directly overhead wherever you are on the planet, and exactly overhead on the equator. The Sun in summer is hotter and it spends a longer time above the horizon.
This concept is worth taking the time to think about as it is just so unintuitive. It is a powerful idea too, as it turns out that it is the tilt that largely determines the seasons for nearly all the planets in our Solar System. It works in the sense that the larger the tilt, the larger the variations between the seasons.
Uranus wins first prize with the largest axial tilt of close to 90 degrees. Meanwhile, Mercury and Jupiter have axial tilts of very close to zero. Earth falls somewhere in the middle at 23.5 degrees. Imagine how life on Earth would be different if the tilt was increased on decreased but just a few tiny degrees!
