We all know that the earth revolves around the sun in an elliptical path.
Most of the people believe that summer happens
when the earth is closer to the sun
and winter happens when the earth is farther
from the sun in its elliptical path.
If you are one among them, "you are wrong".
You might have noticed that the sun is not rising
at the same point in the east throughout the year.
It changes its position gradually in the east.
But do you know that this change in sun rise location
is the reason for the change of seasons on earth?
All of you would have studied that the earth is tilted
23.5 degrees in its axis.
We will look at the reason for this tilt
at the end of this video.
Tropic of cancer is the highest latitude
in the northern hemisphere beyond which
earth doesn't receive vertical solar radiation.
Sun rays hit the tropic of cancer vertically on 21st of June every year.
Corresponding latitude in the southern hemisphere is called the Tropic of Capricorn.
The Tropic of Capricorn receives vertical solar rays on 22nd of December.
If you look at the map or a globe,
you can see these latitudes are marked with 23.5 degrees
which is equal to the amount of earth's tilt to the vertical axis.
When the earth's northern hemisphere is tilted towards the sun,
it gets more amount of solar radiation than that of the south.
As vertical rays travel less distance in the earth's atmosphere,
it is scattered less and the hemisphere of the earth facing the sun receives more heat energy.
It leads to summer season in the northern hemisphere
and winter season in the southern hemisphere.
During the summer season in the northern hemisphere,
the Arctic pole continuously receives sunlight for a period of 6 months.
If you are staying beyond the latitude of 66.5 degrees North,
you can't differentiate between day and night
and you will need the help of a 24 hours watch.
As Norway is located closer to the Arctic circle,
it is called the land of midnight sun.
Sameway, summer happens in the southern hemisphere
when the sun rises vertically above the tropic of Capricorn on December 22.
The Antarctic circle continuously receives sunlight for 6 months.
When this is happening in the southern hemisphere,
it's winter in the northern hemisphere.
So what about the other two seasons, spring and autumn?
During September, the sun rises directly above the equator.
Months of September to November are autumn in the North and spring in the South.
During March, again the sun rises directly above the equator.
Months of March to May are spring season in the North and autumn season in the south.
Autumn is the season when plants shed their leaves in preparation for the upcoming winter.
Spring is the season of rejuvenation, renewal, rebirth and regrowth.
These two seasons are majorly felt in the temperate regions of the two hemispheres.
As this changing effect of sun rays is not felt in the equatorial region,
it doesn't witness different seasons and it is warm and humid throughout the year.
Duration of days and nights are almost the same in equatorial regions.
Now it's time to look at the reason for the earth's tilt.
Earth’s tilt angle was accurately measured as early as 1100 BC in India and China.
The ancient Greeks had good measurements of obliquity since about 350 BC.
Scientists believe that the earth was hit by a big object called 'Theia' during its initial phases of formation.
That impact led to the tilt of the earth.
It also created a big hole and sent a huge amount of dust particles and rubble into the space.
These dust particles slowly combined to form a satellite planet and we humans,
named it as the moon.
What would have happened to the earth if it had not faced that impact?
We won’t have changing seasons across the year
and there will be no season changes like the equatorial region.