Earth Seasons

  • May, 2020

Earth is only planet we know that has any form of life on its surface till now. But if you go backwords when earth is just born, it is same as other planet, early atmosphere was probably mostly carbon dioxide, with little or no oxygen. There were smaller proportions of water vapour, ammonia and methane. As the Earth cooled down, most of the water vapour condensed and formed the oceans and this cycle is beginning of different seasons on earth.


One of the most important factor of our or any life existences is season. There is no doubt that elements like water vapor, oxygen plays major role but because of stable seasons life on earth became more adoptive and flourish.
So it is very important for us to actual physics and astronomy behind it. And to understand above first one image in enough.

So you must be thinking why do I am writing this blog if this is so easy? Well, because its easy many people misunderstand for example, many people think that seasons occurs because earth changes its angle each six month from left to right but that is entirely incorrect. Not only that there are few other thing you must know if you want to understand earth season correctly

So let’s dive into the rotation of our planet into around the sun.

There are few terms you probably know , just quick reminder…

  • Orbit: a course, range, or curved path that is followed revolution and rotation…
    • Revolution: the Earth’s path around the sun
    • Rotation: the movement of earth around its axis
  • Ecliptic: the apparent path of the sun on the celestial sphere over the course of a year
  • Siderial year: the time required for the Earth to reach exactly 1 orbit around the sun
  • Tropical year: the year that our calendar measures Seasons


Now to understand this how season comes and go we have to understand rotation of earth around the sun. we all know that .earth rotates around the sun in elliptical path. Earth takes SIDEREAL YEAR to one complete orbit 365.256 days with 940 million km (584 million mi) travelled and also that Earth is tilted on its axis by 23.5 degrees as earth orbits around the sun, it tilts toward the sun or it tilts away from the sun.
Because Earth is at an angle, the SUN SEEMS to travel at an angle. This apparent path of the sun is called the ECLIPTIC. All the planets stay very near the ecliptic in their orbits.


Don’t worry if you don’t understand how sun change paths shown in above image. Because I am going to explain these in bit. let’s first understand what is solstice ???


Solstice, either of the two moments in the year when the Sun’s apparent path is farthest north or south from Earth’s Equator. In the Northern Hemisphere the summer solstice occurs on June 20 or 21 and the winter solstice on December 21 or 22. The situation is exactly the opposite in the Southern Hemisphere, where the seasons are reversed.


As you can see in above picture Fig1. North pole is tilted 23.5 degree towards the sun. So because of these country in northern hemisphere faces more heat from sun and that’s why they have summer season and south pole is away from sun (in figure1 ) that indicates winter in that countries (southern hemisphere )

Now same goes after 6 months …at 21/22 December..

To be more specific here didn’t change it’s degree 23.5 but its position changes during time…that creates seasons..

As you can see in above picture. North pole is tilted 23.5 degree towards the sun …So because of these country in southern hemisphere faces more heat from sun and that’s why they have summer season and north pole is away from sun (in Fig2 ) that indicates winter in that countries (Northern hemisphere)

so we can say that there are 2 solstice in year…when because of earth angle we face summer and winter season..


So if I put above image in front of you , you can understand what solstice means right..??
Now lets talk about another 2 thing indicates in the above image..

An equinox is an event in which a planet’s subsolar point passes through its Equator. The equinoxes are the only time when both the Northern and Southern Hemispheres experience roughly equal amounts of daytime and nighttime.
On Earth, there are two equinoxes every year: one around March 21 and another around September 22. Sometimes, the equinoxes are nicknamed the “vernal equinox” (spring equinox) and the “autumnal equinox” (fall equinox), although these have different dates in the Northern and Southern Hemispheres.


The yellow dot (in Fig2) is the North Pole. Notice how the pole is 'to the side' of the center of the sun during equinoxes, and directly centered on the sun during solstices. Vernal Equinox March 21/22 Winter Solstice December 21 /2 2 Sun Summer Solstice June 20/21 Autumnal Equinox September 22/23. Before and after the equinox, the subsolar point migrates north or south. After the March equinox, the subsolar point migrates north as the Northern Hemisphere tilts toward the sun. Around June 21, the subsolar point hits the Tropic of Cancer, (23.5°N). This is the June solstice, after which the subsolar point begins to migrate south. After the September equinox, the subsolar point continues to move south as the Southern Hemisphere tilts toward the sun. Around December 21, the subsolar point hits the Tropic of Capricorn (23.5°S). This is the December solstice.


Let’s say from September 22/23 equinox. During the October , November and up to 21-22 December earth’s north pole will be tilted away from sun which creates winter in northern hemisphere and south pole has summer. But after December up to March 21/22 it will be vertical at equator …and we have vernal equinox (spring). And after till the June 21-22 where North Pole faces sun (summer) and south pole far away from sun (In above figure...). At last after June till the September 22-23 fall (autumnal) equinox sun will be vertical to equator. This cycle repeats every year which gives us amazing seasons…