It is taught to us in school that the Length of day and the length of Night are equal on the days of the Equinoxes and days are longest on Summer Solstice and Shortest on winter solstice. Have we ever wondered why this happens?
Lets learn a little about the earth first.
The Earth lies in a zone called the Goldilocks zone. Goldilocks was a little girl who was in jungle one day and she discovered a cottage which everything in three sizes. Small, Medium and Large. Long story short, she was hungry and saw porridge on the dining table. There were three bowls. You guessed it, they were in different sizes too. The porridge in these bowls was hot, cold and luke warm, Goldilocks chose the luke warm porridge. Earth is like Goldilocks. It is at a distance from the Sun which neither too hot or too cold. Just the right temperature. The temperature is just right for water to exist in all three forms. Solid, liquid and gaseous.
Soon after its formation the earth achieved a tilt on its axis. This tilt is 66.5° from its orbital plane (or 23.5° from the perpendicular) and thus gives our planet just enough leverage for the most important phenomenon on Earth; The Seasons.
The exact cause of the tilt is unknown but the best scientific estimate points towards the Giant Impact theory, which also explains why the earth has such a large satellite; something which is abnormal. We will cover this in the next article.
It takes earth a little more than 365 days to complete on revolution around the Sun and we experience 4 seasons. Summer, Autumn, Winter and Spring. These seasons maintain a very delicate balance of nutrient interchange between the Northern and the Southern hemisphere. If the earth was not tilted on its axis, the seasons wouldn’t have been possible because the amount of sunlight received by both the hemispheres throughout the year would be in a particular pattern. Maximum Sunlight at the Equator and lesser sunlight as you move towards either of the Poles.
As the axis points towards only area of the sky. If you notice the diagrams above carefully, you will notice that the difference of sunlight received by both the hemispheres is drastically different from each other on the day of the summer and the winter solstice. This is true for most of the season as these dates lie right in the middle of summer and winter respectively. Whichever area receives more sunlight, also receives it for a longer duration due to the curvature of the earth. That is why summers are hot and winters are cold. The effects of these seasons are felt the best in the sub-tropical temprate zones. India is one of the counties where these seasons are felt in full extent. Areas just beyond the Arctic and Antarctic circles get 24 nights during winters and 24 hour days during summers.
There also comes a time when just because of the tilt of the axis, neither of the hemisphere receives more light than the other. These are the equinoxes. Length of the day and night are equal all across the world, the Sun rises precisely from the East and sets precisely in the west, At local noon, people loose their shadows if they are at the equator. There are so many events which happen on this day.
The ones which are most noticeable by us are arrival of summers after the Spring Equinox and the arrival of winters after the Autumn equinox (in Northern Hemisphere).
These seasons are very important for the survival of life on earth as everything we do is dependant on it. Plants and animals follow a yearly cycle of the seasons and complex life cycle stages are triggered by gradual change in temperature and sunlight which are caused by seasons. In the span of a year, due to their geographical position on the earth, places near the equator receive the most sunlight and heat whereas the polar regions receive the least sunlight and heat. To experience all seasons properly, you need to be in the middle of the temperate zone (the sweet spot)
Remember, Equinoxes and Solstices don’t mark the beginning of a season, but the middle of it.