why do we have seasons on earth

It's all about Earth's tilt! Many people believe that Earth is closer to the sun in the summer and that is why it is hotter. And, likewise, they think Earth is farthest from the sun in the winter. Although this idea makes sense, it is
incorrect. It is true that Earth s orbit is not a perfect circle. It is a bit lop-sided. During part of the year, Earth is closer to the sun than at other times. However, in the Northern Hemisphere, we are having winter when Earth is closest to the sun and summer when it is farthest away! Compared with how far away the sun is, this change in Earth's distance throughout the year does not make much difference to our weather. There is a different reason for Earth's seasons.


Earth's axis is an imaginary pole going right through the center of Earth from "top" to "bottom. " Earth spins around this pole, making one complete turn each day. That is why we have day and night, and why every part of Earth's surface gets some of each. Earth has seasons because its axis doesn't stand up straight. But what caused Earth to tilt? Long, long ago, when Earth was young, it is thought that something big hit Earth and knocked it off-kilter. So instead of rotating with its axis straight up and down, it leans over a bit. By the way, that big thing that hit Earth is called Theia. It also blasted a big hole in the surface. That big hit sent a huge amount of dust and rubble into orbit.


Most scientists think that that rubble, in time, became our Moon. As Earth orbits the sun, its tilted axis always points in the same direction. So, throughout the year, different parts of Earth get the sun s direct rays. Sometimes it is the North Pole tilting toward the sun (around June) and sometimes it is the South Pole tilting toward the sun (around December). It is summer in June in the Northern Hemisphere because the sun's rays hit that part of Earth more directly than at any other time of the year. It is winter in December in the Northern Hemisphere, because that is when it is the South Pole's turn to be tilted toward the sun.


Although this idea makes sense, it is incorrect. It is true that Earth s orbit is not a perfect circle. It is slightly elongated, so that during part of the year, Earth is closer to the Sun than at other times. However, in the Northern Hemisphere, we are having winter when Earth is closest to the Sun and summer when it is farthest away! There is a completely different reason for Earth's seasons. Earth has seasons because sometime early in its long history, something very big hit the young Earth to knock it off-kilter. So instead of rotating with its axis perpendicular to its orbital plane, it is tilted 23. 45 degrees from the perpendicular. Incidentally, that big something that hit Earth also knocked a chunk of it out that became our Moon.


At least that is generally accepted theory. So, here we are, orbiting the Sun, but tilted a bit and always with the axis pointed in the same direction. So different parts of Earth get the Sun s direct rays as we travel through the year. Thus, sometimes it is the North Pole tilting toward the Sun (like in June) and sometimes it is the South Pole tilting toward the Sun (like in December). Hence, the seasons. It is summer in June in the Northern Hemisphere because the Sun's rays hit that part of Earth more directly than at any other point in Earth's orbit - or, in other words, more directly than at any other time of the year.


It is winter in December in the Northern Hemisphere, because that is when it is the South Pole's turn to be tilted toward the Sun. It follows that if you live in North America, during the winter the Sun s path across the sky is more toward the south, rising in the southeast and setting in the southwest. During the summer, the Sun tracks more directly overhead, rising in the east, overhead at noon, and setting in the west. If you live in the Southern Hemisphere, the Sun will be more northerly in the sky during the winter (that is, June, July, and August). So if you go to South Africa for the winter holidays, bring your swimsuit and leave your skis at home.