Why Do We Have Seasons?? - The Science Behind It !!

in #science7 years ago (edited)


The season is a short period of a year with particularly different weather patterns and daylight hours as a result of earth's changing position with regard to sun.

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We sit by our window, keep looking when day becomes night and night becomes day, bringing with it the snow of winter, the heat of summer, the freshness of monsoon, the aura of spring and the pleasure of autumn.

I'm sure all of us has noticed seasonal changes year after year but how many among us come to think of it ?? Probably very few. We are so used to them that we don't even think about them very often. 

These types of changes differs depending on where we live.

In the tropics, it never gets cold but is warm and hot all the time. Yeah but, we can discuss about dry season and rainy season.

The arctic  areas are mostly cold all the time with some places with months straight without any sunlight.

And in the temperate areas, we basically have four seasons. 

Plants bloom in the spring, summer gets scorching hot, leaves fall in the autumn and winter gets uncomfortably cold. 

But why? Do we ever wonder how we see these amazing changes and when we unveil, it is nothing short of miracles?

WHAT IS THE SEASON?

It is a short period of a year with particularly different weather patterns and daylight hours as a result of earth's changing position with regard to sun. This period divides one year into several parts during which the seasonal conditions of the day, temperature, rainfall, humidity, etc., as a result of the orbiting the Earth's Sun, change in a cyclic form. The effect of this cyclical change falls on ecosystem and thus the ecological seasons are created.

WHAT'S WRONG KNOWING A BIT ABOUT CLIMATE AND WEATHER TOO??

So weather is the location of the atmosphere, at any time. There are many factors in it, such as the air temperature, pressure,humidity, speed and direction of the wind and cloud, fog, rain, snow etc., and their interactions. 

These interactions mainly determine the weather of a place. And if any of these interactions occur at some place for a long time, for example, for a full year, it is called "climate" of that place. 

The weather can change every day but many times in the day. The climate does not change easily. Changing the climate of a place can take not thousands but millions of years. That's why we talk of 'changing weather' not 'changing climate'. And that is also why we read about the weather, in newspapers, listen in the radio and watch on television.

So lets move further.

THE MYTH

It has just been few years, I myself got the fact cleared about this particular topic. 

Why is summer hot? and winter cold? -- Because the earth is near the sun in the summer and away from the sun in winter. Simple, isn't it?

Like me, I guess most of the people believed or may still believe the same. 

But let's address the fact.

The distance between earth and Sun around 3 January is 147.1 million km, whereas the distance around 4 July is 152.1 million km. The difference between the two positions comes to about 5 million km which is negligible on this scale and not so much that it can have an effect on the weather on Earth. 

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So friends... It seems to be true on the surface but it is actually wrong.

SO WHAT IS THE REAL CONCEPT??

As we have been taught from our childhood that the Earth rotates on an axis tilting, spinning and simultaneously it revolves around the Sun in an elliptical or oval orbit taking one long year comprising of 365 days. The cause of season is also because of the earth's tilt on its axis and its revolution around the sun. But How? 

Axis of the Earth is an imaginary line on which the Earth rotates and it links the two poles - the North and the South Pole. This axis on the earth is tilted 23.45 degrees relative to the ecliptic plane around the sun which also affects the sun's rays falling on the earth.

   

Because of this tilt, one hemisphere of the Earth is tilted towards the Sun for six months and the next six months, the other hemisphere.

As a result, this tilt causes one hemisphere to receive direct sunlight as it gets comparatively closer to the sun i.e. the sun’s rays are striking that part of Earth at a more direct angle hence resulting in summer while the other hemisphere receives slightly slanting rays as it is comparatively farther from the sun hence less intense heat, resulting in winter. The hemisphere that is tilted towards or away from the Sun changes, as the Earth travels around the Sun.

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This gives us the four seasons of the year - Spring, Summer, Autumn (Fall) and Winter.

So, it is understood that due to this inclination of the Earth's axis, the northern and southern hemispheres have different seasons at the same time of the year. In short, Northern summer = Southern winter. 

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So ?? This is it then??

Lets go a bit deeper.

For that, we have to understand three important terms - Overhead sun, Equinox and Solstice.

What are these?

When the Sun is directly overhead the Earth's surface and forms a 90-degree angle, it is overhead sun. The variations in the angle of overhead  Sun causes variations in solar radiation received at different periods and locations. 

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Equinoxes are days where overhead sun is on the equator on all places of the Earth, giving equal duration of day and night.

Spring Equinox - On 21 or 22 March, the overhead sun receives maximum sunlight as it is over the equator. On this day, two hemispheres get an equal amount of solar radiation and on all the places on earth, the equal length of day and night is observed. After this day, the northern hemisphere has longer days and shorter nights spring and the Southern Hemisphere has shorter days and longer nights autumn.

Autumn Equinox - On 22nd or 23rd of September, the overhead Sun is once again over the Equator.  It has equal length of day and night in both the hemispheres. At this time the Northern hemisphere experiences Autumn and the Southern hemisphere experiences Spring. 

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The Solstices are the days when the sun reaches its farthest north and south declination.

In Summer Solstice(21st or 22nd of June), the overhead Sun is perpendicular to the Tropic of Cancer. This day the Southern hemisphere is in Winter solstice and Northern Hemisphere is in Summer solstice. At this time, Northern hemisphere experiences summer with the day being the longest day of the year while Southern hemisphere experiences winter with the day being the shortest day of the year. The Arctic circle has 24 hours of daylight on this day while Antarctic circle experiences 24 hours of darkness. 

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Winter Solstice (on 21st or 22nd of December), the overhead Sun is over the Tropic of Capricorn. This day the Northern hemisphere is in Winter solstice and Southern Hemisphere is in Summer solstice. At this time, Southern hemisphere experiences summer with this day being the longest day of the year while Northern hemisphere experiences winter with the day being the shortest day of the year. The Antarctic circle has 24 hours of daylight on this day while Arctic circle experiences 24 hours of darkness. 


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Summary

To consider the difference in distance of our planet from the sun as the reason for change in the weather seems logical. But the distance from the sun to the earth is not enough to create seasonal differences. Instead, our season varies because the earth tends to tilt on its axis.

Thus it is clear that due to the inclination of the earth, there is variation in temperature in different hemispheres of the north and south. The variance of the earth's inclination and the sun's rays is also a great factor to determine climate as the sun's effect on our oceans. Warming ocean creates vaporization in the ocean and warming or cooling of the oceans also forms convective currents. These two together can cause energy to transfer around the atmosphere and oceans to create a climatic condition.

To give a couple of examples.Other planets like- 

Uranus rotates sideways at 97 degrees and has utmost and bizzare seasons.

Also,Venus's axial tilt is 177.3 degrees. 

So how well can we handle our seasonal Ups and Downs??


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