The seasons change as Earth orbits the sun. Earth’s hemispheres receive different amounts of sunlight during each season because of the 23.5 degree tilt of Earth’s axis. When the Earth is at a point in its orbit that the northern hemisphere is tilted toward the sun, it is summer for the northern hemisphere. This is because the northern hemisphere receives the most direct sunlight and longer daylight hours, which allows it to heat up and stay warm. More sun rays cover a larger area, so the area is warmer.
The point in the year when the northern hemisphere is tilted most toward the sun and in turn receives the most sunlight is the June solstice. After that, the northern hemisphere is still tilted toward the sun, but less directly. As time passes, the northern hemisphere points less and less directly at the sun. The September equinox is when the northern hemisphere actually begins to be tilted away from the sun. The northern hemisphere receives less and less direct sunlight and begins to cool down. As the northern hemisphere cools down, it becomes fall and then winter, when the axis is pointed away from the sun.
The December solstice refers to the time of year when the northern hemisphere is pointed furthest away from the sun. It is winter because sun rays have to cover a larger area and thus do not heat it as much. After the December solstice, the season slowly becomes more moderate. Earth’s axis gradually becomes less pointed away from the sun, and the northern hemisphere slowly receives more and more direct sunlight. At the March equinox, the northern hemisphere actually becomes slightly tipped toward the sun and is no longer pointed away. The northern hemisphere gradually warms and receives more direct sunlight until the June solstice.
The solstices are interesting because they refer to the moments when the Earth’s axis is tipped the furthest away or closest toward the sun. At both equinoxes, the northern and southern hemispheres are tilted neither away nor toward the sun. For instance, at the March equinox, the northern hemisphere changes from being tilted slightly away from the sun to slightly more tilted toward the sun and the southern hemisphere changes from being tilted slightly toward the sun to slightly tilted away from the sun. At the equinoxes, because of the Earth’s position in orbit and tilt neither away nor toward the sun, the sun rises directly due east and sets directly due west and the Earth receives equal amounts of daytime and nighttime.
What do you think seasons would be like if Earth’s axis had no tilt? Do you think we would still have different seasons? Why?
