Why do we have winter-spring-summer-fall?

Friday, October 30, 2020

I live in a portion of the US that experiences seasons. I enjoy summer but then look forward to the fall and cooler weather, and then winter is a change of pace and snow is fun, and then I welcome spring and warmer weather. I love having seasons, but what causes these seasons?

why seasons

The seasons are caused in part by the tilt of the Earth. The Earth is 23.44 degrees.

tilt of earth

As the Earth revolves around the sun the hemisphere tilted towards the Sun experiences summer, and winter occurs in the hemisphere tilted away from the Sun. During the spring and the fall, the tilt of the Earth is between summer and winter. 

The hemisphere that is tilted towards the Sun is warmer because sunlight travels more directly to the Earth’s surface and less of the sunlight less is scattered in the atmosphere. In the winter the sunlight is more indirect. 

Let's see what this looks like. I took a flashlight and cardboard and tilted the cardboard at the same angle as the Earth is tilted in the summer. I then traced the light and did the same thing when it is winter. As you can see the sunlight is more concentrated in the summer compared to the winter.

sunlight during summer

The more concentrated the light the warmer the temperature the more indirect the light is like in winter the cooler the temperatures. The hemisphere that’s tilted closest to the Sun has the longest, brightest days and the hemisphere tilted away from the sun has the shortest days. At the equator, there are no seasons because each day the Sun strikes at about the same angle. Every day of the year the equator receives about 12 hours of sunlight.

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