March Equinox 2021 – First Day of Spring in Northern Hemisphere

March Equinox marks the arrival of the first day of spring in the northern hemisphere. That’s why in the earth’s northern areas, the March equinox is known as the spring equinox. In 2021, the March equinox will occur on Saturday, March 20, at sharp 5:37 Eastern Daylight Time (EDT).

On the other hand, for the people living in the southern hemisphere, this equinox marks the arrival of the first day of fall (autumn) in the southern hemisphere. That’s why in the earth’s southern areas, the March equinox is known as the Fall Equinox.

In other words, the meaning of equinox changes depending on the fact that at what side of the hemisphere you live upon. Not to mention, regardless of the fact that at which side of the hemisphere you live upon, the length of day and night are almost exactly equal on the eve of Equinox. CONFUSED??? Don’t worry, we will talk about it in the later section.

Moving ahead, in this exclusive article, we will talk about the fact that why there is a mismatch between the north and south equinoxes? Or, the March Equinox i.e the first day of spring in the northern hemisphere is actually the official first day of spring or not? Therefore, I would suggest you stick with me till the end. Let’s dive right in!!!

 

What is Equinox?

There are two ways to define the meaning of equinox. These are astronomical and meteorological definitions of Equinox. Right now, I am going to explain it on the basis of astronomy. But that doesn’t mean I won’t be explaining the meteorological definition of equinoxes. We will talk about it in the later section.

So, moving ahead, according to the astronomical definition of the equinox, this is a naturally occurring event during which the center of the sun appears to cross over the celestial equatorial line of the earth. In layman, one can say that an equinox occurs when the sun switches side from one hemisphere of the earth to the other.

Not to mention, there are two types of equinoxes. Spring Equinox, also known as Vernal equinox that marks the first day of spring. And the Autumn Equinox, also known as the Fall equinox that marks the first day of fall.

Highly recommended, March Equinox – First Day of Fall in Southern Hemisphere

Four Seasons

Just to let you know, there are generally four seasons that occur on earth. These are summer, winter, autumn, and spring. Just like spring and autumn equinox is responsible for the arrival of spring and autumn seasons on earth.

types-of-seasons-image
Four types of seasons that occurs on earth: (above) Winter, Spring, (below) Summer, Autumn/Fall

In a similar way, the summer and winter solstice is responsible for the arrival of summer and winter season on earth. To summarise, each year earth experiences 2 solstices (summer and winter) and 2 equinoxes (spring and fall) that help us to understand the patterns related to the changing seasons.

Now, the question arises that why we see a mismatch between the north and the south. In other words, why when there is the spring equinox in the northern hemisphere, there is the autumn equinox in the southern hemisphere? Let’s find out!!!

Must Read: Equinox vs Solstice – What’s the Difference?

 

Thnx to Earth’s Tilt, we See Equinoxes

earth's-tilt-reason-for-seasons
Earth’s axial tilt (obliquity) is currently about 23.4°/Credit: Wikimedia Commons

Well, there is a small correction here. Not only we see equinoxes because of the earth’s tilt. We see solstices too. Moving ahead, just because the earth has an axial tilt of 23.4 degrees, there is a mismatch between the northern and the southern hemispheres.

In fact, Kepler’s law also contributes to the formation of the different seasons across the globe. YES, YES, the same Kepler’s law that states that all the planets in the solar system revolve around the sun in an elliptical orbit.

However, Kepler’s law contribution can’t be compared to the role played by the earth’s tilt. I mean, if I say in terms of approximated ratios. Then it will be like 90:10.

Basis of Comparision Northern Hemisphere Southern Hemisphere
March Equinox In the northern hemisphere, it marks the arrival of spring, therefore, Spring Equinox. In the southern hemisphere, it marks the arrival of autumn, therefore, Autumn Equinox.
June Solstice It marks the arrival of summer, therefore, Summer Solstice. It marks the arrival of winter, therefore, Winter Solstice.
September Equinox Marks the arrival of autumn, therefore, Autumn Equinox. Marks the arrival of spring, therefore, the Spring Equinox.
December Solstice It marks the arrival of winter, therefore, Winter Solstice. It marks the arrival of summer, therefore, Summer Solstice.
From the above comparison chart, it is clear that the equinox that occurs in March in the northern hemisphere is the Spring Equinox. On the other hand, due to the earth’s tilt, the equinox that occurs in March in the southern hemisphere is the Autumn Equinox.

 

March Equinox – First Day of Spring in Northern Hemisphere

spring-equinox-in-northern-hemisphere
An image of the first day of the spring of the Indian Union territory of Jammu and Kashmir. Image Credit: Glyph Web

As you already know that an equinox occurs when the center of the sun appears to cross over the celestial equatorial line of the earth. Moreover, you also know that there are two types of Equinox. These are march equinox and September equinox.

So, how to define March Equinox or even September equinox. OKAY, let me rephrase my question for you!!! What’s the difference between the march and September equinox? Any Guess???

Well, the only difference between the march and September equinox is that during march equinox, the sun switches side from the southern hemisphere to the northern hemisphere of the earth. That’s why the march equinox is also known as the Northward equinox.

On the other hand, during September equinox, the sun switches side from the northern hemisphere to the southern hemisphere of the earth. That’s why the September equinox is also known as the Southward Equinox.

Take a look at December Solstice: First Day of Winter in Northern Hemisphere

March Equinox – Northward Equinox

earth's-illumination-during-different-season-in-different-hemisphere
Image Credit: Wikimedia Commons

Moving ahead, as the sun crosses over the imaginary celestial line from the south to the north direction. The earth’s northern areas start to warm up rapidly. Refer to the above image for proper understanding.

Check Out: What are Lines of latitude? Definition & Diagrams

Hence, marking the end of the winters and the arrival of the first day of spring in the northern hemisphere. That’s why the march equinox is officially known as the spring or vernal equinox in the northern parts of the earth.

Similarly, as the sun crosses over the imaginary celestial line from the south to the north direction. The earth’s southern areas will start to cool down rapidly.

Hence, marking the end of the summers and the arrival of the first day of fall (autumn) in the southern hemisphere. That’s why the march equinox is officially known as the fall equinox in the southern parts of the earth.

Must read, Snow Moon: Last Full Moon Before Spring Equinox in Northern Hemisphere

Equal Day and Night

equal-day-and-night-during-equinox
Illumination of Earth by the Sun on the day of the equinox (fall or spring). Image Credit: Wikimedia Commons

Yup, you heard me right. We have equal day and night during march equinox (also during September equinox). WHY? Because when the sun crosses over the imaginary celestial line, the earth’s tilt becomes perpendicular to the sunshine. Or, you can say that on the eve of an equinox, the earth’s axis is neither tilted toward nor away from the sun.

Hence, daylight and nighttime hours are equal. In other words, we will have equal day and night i.e 12 hours. Don’t think that the earth’s axial tilt will become Zero during the equinoxes. In fact, it just happens because of the sun’s passing over the Equatorial line.

Moving ahead, in the light of equal day and night phenomena, I just want to clarify that it’s not exactly equal. It’s nearly equal to 12 hours. Therefore, just for approximation, we simply say that during the vernal equinox and autumnal equinox, the length of day and night becomes equal.

Must read, December Solstice: First Day of Summer in Southern Hemisphere

Longer Days Shorter Nights

beach-in-usa-after-the-arrival-of-spring-equinox-in-northern-hemisphere
This is how an American beach looks like in the month of March after the arrival of spring. Image Credit: Steve Nesius/Reuters

There are two ways to practically observe the first day of Spring. First, you will feel that the weather starts to turn warmer, trees begin to grow their leaves, plants start to flower, etc. Second, You can notice that the days are getting longer and the nights are getting shorter.

In other words, after Spring equinox 2021, as the sun will start to move northward, the days will become longer and longer with each passing day. Not to mention, for the people living in the northern hemisphere, this process of longer days shorter nights will go on until the arrival of the June solstice.

Editor’s Choice: Full Moon in March – First full moon after the arrival of spring in northern hemisphere

 

Spring Equinox – First Day of Spring or Midspring?

Now is the time that we should talk about the meteorological definition of the spring equinox. Well, technically speaking, if we go by the meteorological definition of the spring equinox, it marks the end of the half of the spring season i.e mid-spring.

However, on the other hand, if we go by the astronomical definition of the spring equinox, it marks the arrival of the first day of the spring. Therefore, the question arises that why we have two different definitions for a single event. More importantly, which one of these is the correct one? Let’s find out.

Let’s Go Back in Time

Before the arrival of the scientific revolution, humans didn’t know how to calculate the change in the season in terms of astronomical calculations. WHY? Because they didn’t have the telescope to do such nasty observations.

Therefore, what they used to do is to calculate the change in season as humanly as possible. With time, early humans understood that the sun seems to cross over the horizon after a fixed interval of time. Additionally, they also understood the pattern of the annual temperature cycle.

In other words, what early humans used to do is to calculate the relative things, like what they felt and observed with the naked eyes, which is in fact in the modern notation is known as the meteorological definition of spring equinox or simply meteorological spring.

On the other hand, what our astronomers and scientists calculate with their super-sophisticated technology is defined as the astronomical definition of spring equinox or simply astronomical spring.

Therefore, to conclude, I would say that both definitions are correct in their own sense. Hence, as a result, some people define the spring equinox in the northern hemisphere as the first day of the spring.

Editor’s Choice: June Solstice 2021 – First Day of Summer in Northern Hemisphere

On the contrary, some people define it as the end of the half of the spring season, hence mid-spring. Not to mention, the meteorological seasons always arrive approx 20 days before the arrival of astronomical seasons. To understand it more clearly, refer to the below table.

 

Meteorological vs Astronomical Seasons

Seasons Meteorological Seasons Dates Astronomical Seasons Dates
Spring Equinox Monday, 1 March 2021 Saturday, 20 March 2021
Summer Solstice Tuesday, 1 June 2021 Monday, 21 June 2021
Autumn Equinox Wednesday, 1 September 2021 Thursday, 23 September 2021
Winter Solstice Wednesday, 1 December 2021 Tuesday, 21 December 2021
All the seasons (meteorological and astronomical) dates are strictly in accordance with the northern hemisphere of the earth.

 

When is the Spring Equinox 2021 in the Northern Hemisphere?

This year’s March Equinox i.e the spring equinox in the northern hemisphere will happen on Saturday, March 20, at sharp 5:37 Eastern Daylight Time (EDT). Not to mention, this astronomical event will occur at the same moment for all of us.

I mean, whether you are living in London or in India, or even in Australia (i.e in the southern hemisphere), it would be a moment of joy for all of us at the same instant. Well, yeah, for Aussies, it will be the fall equinox. I hope that now you know the exact reason behind it.

Editor’s Choice: June Solstice 2021 – First Day of Winter in Southern Hemisphere

That’s it for this post. If you like this article, share it if you like it, like it if you share it. You can also find us on Mix, Twitter, Pinterest, and Facebook.

 

I am a mechanical engineer by profession. Just because of my love for fundamental physics, I switched my carrier, and therefore I just completed my postgraduate degree in physics. Right now I am a loner (as like ever) and a Physics blogger too. My sole future goal is to do a Ph.D. in theoretical physics, especially in the field of cosmology. Because in my view, every part of physics comes within the range of cosmology. And I love traveling, especially the Sole one.

Leave a Comment