Why are there seasons?

Why are there seasons?

Every area of the earth experiences the four seasons. Depending upon where you live, the seasons can be different. We divide these seasons into spring, summer, fall and winter. Some areas of the planet experience extremely hot or extremely cold temperatures, while others vary lightly or are even mild. The reason that we have the seasons has to do with how the earth is tilted.



seasonsIf you asked the average person why the earth has seasons, they would probably say ‘because the earth is closer to the sun in summer and farther away in the winter’.  This is not completely true. It all has to do with the fact that the earth is tilted and rotates on an axis. If you look at any globe in the school or library, you will notice that it is set up on an angle and not straight up and down.  This angle is known as the axis of the earth.



The earth experiences the seasons differently, depending upon where you are on the earth and the time of the year. As the earth rotates around the sun, different ‘hemispheres’ of the earth are colder or more warm. When the northern hemisphere of the planet is tilted farther away from the sun and this makes their winters colder because they don’t get as much sun as other areas. The axis stays in this direction for six months and then for the next six months it shifts so that the northern hemisphere is closer to the sun but the southern hemisphere is pointed away.



Whichever hemisphere is pointed towards the sun receives more energy from the sun. Areas like the North and South Pole never receive as much energy as the rest of the planet. When the earth is tilted towards the sun our days are longer, when pointed away, the days are shorter. The longest day in summer is called the Summer Solstice and the shortest is called the Winter Solstice.  There are times during the cycle where all hemispheres get the same amount of the sun’s energy. This time period is called the ‘equinox’. This occurs twice each year, once in the spring and once in the autumn.  During the equinox, the length of the days and nights are equal.



There is one more variation that causes temperature extremes for the seasons, and this does involve the distance of the earth to the sun.  The intensity of the weather depends on the distance that the hemisphere is from the sun. This is why the Northern Hemisphere experiences such intense cold and snow during the winter.



Something that is interesting to know is that the earth’s axis is actually changing. A complete ‘cycle’ of the earth’s axis is measured in 26,000 years.  Every 13,000 years, the seasons are actually reversed.  It takes another 13,000 years for them to return back again. This change is so gradual that you probably would never notice it, but it does cause the Summer Solstice to arrive early every year by twenty minutes. In 70 years, it will arrive a full day earlier.