Goodbye, Winter; Hello, Spring

This day, 21 March, marks the first day of spring in the northern hemisphere, where all of India resides, and autumn in the southern hemisphere.

The day is referred to as the spring or vernal equinox.

During the equinox, the Sun shines on the equator, with each hemisphere receiving the Sun’s rays equally, because of which we get nearly equal amounts of day and night. 

Hence, the word “equinox” — it comes from the Latin words “aequus” (equal) and “nox” (night).

The Sun crossed the Earth’s equator in the middle of the night, at 2.54am, India time.

“On this day, the whole planet -- pole to pole -- gets equal daylight and nighttime. One of four days in our orbit that mark the change of seasons:  Two equinoxes (March & Sept) & two Solstices (June & Dec),” astrophysicist and science communicator Neil deGrasse Tyson said in a tweet.

As opposed to the equinox is the solstice, when either the daytime or nighttime dominates.

The equinoxes and solstices signal the changing of the seasons on Earth.

Why the Earth has all these different seasons is because the axis around which the planet spins doesn’t go straight up and down. 

Earth happens to be titled to one side, thought to have been a result of a hit it once took from another planet billions of years ago. (Incidentally, this also led to the eventual formation of the Moon).

So, the Earth is tilted to one side, by about 23.5 degrees, and spinning as it goes around the Sun. Therefore, through the year, different parts of Earth get the Sun’s direct rays.

If not for Earth’s tilt, the planet wouldn’t have had seasons — at least not in the way that we know them!

The amount of sunlight a given location receives would have been fixed. In a sense, every day would be an equinox. 

On the March equinox day, the Sun shines equally on the northern and southern hemispheres. It is spring in the northern hemisphere and autumn in the southern hemisphere.

On the next equinox, which comes in September, it's a role reversal — it is autumn in the northern hemisphere and spring in the southern hemisphere.

For now, around the March equinox, witness earlier sunrises and later sunsets.

The days will get longer and the nights shorter, bringing in warmer weather, as we head towards the summer solstice in June, initiating the summer season on 21 June.

Interestingly, the Hindu new year day, celebrated as Ugadi in Andhra Pradesh, Telangana, and Karnataka and as Gudi Padwa in Maharashtra and Goa, falls on 22 March, a day after the spring equinox.

In addition, the Persian new year, Nowruz, falls on the first day of spring.