March Equinox 2021 – First Day of Fall in Southern Hemisphere

March equinox marks the arrival of the first day of fall in the southern hemisphere. That’s why in the earth’s southern areas, let’s say in Australia, the March equinox is known as the fall equinox or autumn equinox. In 2021, the March equinox will occur on Saturday, March 20, at sharp 21:37 Australian Eastern Daylight Time (AEDT).

On the other hand, for the people living in the northern hemisphere, this 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 or vernal equinox.

In other words, the meaning of equinox changes depending on the fact that at which 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.

Moving ahead, in this exclusive article, we will talk about the fact that why there is a mismatch between the south and north equinoxes. In other words, why the march equinox i.e the first day of autumn in the southern hemisphere is the first day of spring in the northern hemisphere?

Or, the march equinox i.e the first day of fall is actually the official first day of fall 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 meteorological and astronomical 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. Fall equinox, also known as the autumnal equinox that marks the first day of fall. And the Spring Equinox, also known as Vernal equinox that marks the first day of spring.

Highly recommended, March Equinox – First Day of Spring in Northern Hemisphere

Four Seasons

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

In case if you don’t know, there are generally four seasons that occur on earth. These are summer, winter, autumn, and spring. Just like the fall and spring equinox is responsible for the arrival of fall and spring seasons on earth.

In a similar way, the winter and summer solstice is responsible for the arrival of winter and summer 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 there is a mismatch between the south and north. To put it differently, why when there is a fall equinox in the southern hemisphere, there is a spring equinox in the northern hemisphere? Let’s find out!!!

Highly Recommended: Equinox vs Solstice – What’s the Difference?

 

Thanks 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 southern and northern 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 ComparisionSouthern HemisphereNorthern Hemisphere
March EquinoxIn the southern hemisphere, it marks the first day of fall, therefore, Fall or Autumn Equinox.In the northern hemisphere, it marks the first day of spring, therefore, Spring or Vernal Equinox.
June SolsticeIt marks the first day of winter, therefore, Winter Solstice.It marks the first day of summer, therefore, Summer Solstice.
September EquinoxMarks the first day of spring, therefore, Spring Equinox.Marks the first day of fall, therefore, Fall Equinox.
December SolsticeIt marks the first day of summer, therefore, Summer Solstice.It marks the first day of winter, therefore, Winter Solstice.
From the above comparison chart, it is clear that the equinox that occurs in March in the southern hemisphere is the Fall Equinox. On the other hand, due to the earth’s tilt, the equinox that occurs in March in the northern hemisphere is the Spring Equinox.

 

March Equinox – First Day of Fall in Southern Hemisphere

first-day-of-fall-in-australia
An image of the first day of fall i.e autumn in Australia. Image Credit: Australian Broadcasting Corporation

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.

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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.

Must read, December Solstice: First Day of Summer in Southern 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 southern areas start to cool down rapidly. Refer to the above image for proper understanding.

Hence, marking the end of the summers and the arrival of the first day of fall in the southern hemisphere. That’s why the march equinox aka northward equinox is officially known as the fall or autumn equinox 2021 in the southern hemisphere.

Must Read: June Solstice 2021 – First Day of Summer in Northern Hemisphere

Similarly, 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.

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.

Equal Day and Night

equal-day-and-night-during-first-day-of-fall-or-spring
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.

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

Shorter Days Longer Nights

winter-after-first-day-of-fall
Winter picks up pace after the arrival of fall in the southern hemisphere. Image Credit: Adobe Stock

There are two ways to practically observe the first day of Autumn in the southern hemisphere. First, you can see the sudden change in the color of the leaves around you. I mean, the way your surrounding will become vibrant, it can’t go unnoticed. Second, You can notice that the days are getting shorter and the nights are getting longer.

In other words, after Fall equinox 2021, as the sun will start to move northward, days will become shorter and shorter with each passing day. For the people of the southern hemisphere, this process of shorter days longer nights will go on until the arrival of the June solstice.

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Fall Equinox – First Day of Fall or Midfall?

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

However, on the other hand, if we go by the astronomical definition of the fall equinox, it marks the arrival of the first day of the fall. 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 fall equinox or simply meteorological fall.

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

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

On the contrary, some people define it as the end of the half of the fall or autumn season, hence mid-fall. 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

SeasonsMeteorological Season DatesAstronimocal Season Dates
Fall EquinoxMonday, 1 March 2021Saturday, 20 March 2021
Winter SolsticeTuesday, 1 June 2021Monday, 21 June 2021
Spring EquinoxWednesday, 1 September 2021Thursday, 23 September 2021
Summer SolsticeWednesday, 1 December 2021Tuesday, 21 December 2021
All the seasons (meteorological and astronomical) dates are strictly in accordance with the southern hemisphere of the earth.

 

When is the First Day of Fall 2021 in Southern Hemisphere?

This year’s March Equinox i.e the fall equinox in the southern hemisphere will happen on Saturday, March 20, at sharp 21:37 Australian Eastern Daylight Time (AEDT).

Not to mention, this astronomical event will occur at the same moment for all of us. I mean, whether you are living in New Zealand or in Australia, or even in Europe (i.e in the northern hemisphere), it would be a moment of joy for all of us at the same instant.

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

Well, yeah, for European people, it will be the spring equinox. I hope you know the exact reason behind it.

That’s it for this post. If you like this article, share it if you like, 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.

2 thoughts on “March Equinox 2021 – First Day of Fall in Southern Hemisphere”

    • Hey John,
      Well, in my view, both are the same. However, as you have mentioned, I would definitely love to do some tweaks and changes as per your wish. Keep visiting us!

      Reply

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