Our seasons, winter, spring, summer and autumn, occur because our planet is tilted on its axis 23.5° from straight up-and-down.
Since the top of the axis (see the figure below) always points to the same spot in space, different portions of the planet point at the sun at different times of the year.
On the winter solstice (December), the northern hemisphere is oriented so that it is NOT pointed at the sun. Rather, the southern hemisphere gets the direct rays of the sun. "Direct" means most-directly-overhead. (The following figure illustrates the sun's rays on the first day of northern hemisphere WINTER.)
On the spring equinox (March) and the autumnal equinox (September), the earth is evenly balanced in its orientation with the sun. The direct rays of the sun are over the equator. (The following figure illustrates the sun's rays on the spring and autumn equinoxes.)
On the summer solstice (June), the northern hemisphere is pointed toward the sun. (The following figure illustrates the sun's rays on the summer solstice.)
If it weren't for the tilt of our planet, we wouldn't experience seasons.
The following figure illustrates the sun's path through the sky on each of the seasons' first day. Notice how the sun is high in the sky on June 21st and low in the sky on December 21st. Standing outside and observing the position of the sun at noon through the seasons will give you an idea of the sun's changing pathways in our sky throughout the calendar year. Again, this is all because the earth is tilted on its axis.
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