March Equinox marks the arrival of the first day of autumn in southern hemisphere. That’s why in earth’s southern areas, March Equinox is known as autumn Equinox or Fall Equinox. In 2023, the first day of autumn in Australia (southern hemisphere) will occur on Tuesday, March 21 at 08:25 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 a 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 sides 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 marks the first day of autumn. And the Spring Equinox, also known as Vernal equinox marks the first day of spring.
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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 seasons 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!!!
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Thanks to Earth’s Tilt, We See Equinoxes
Well, there is a small correction here. Not only 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 Comparision||Southern Hemisphere||Northern Hemisphere|
|March Equinox||It marks the first day of autumn||It marks the first day of spring.|
|June Solstice||It marks the first day of winter.||It marks the first day of summer.|
|September Equinox||It marks the first day of spring.||It marks the first day of fall.|
|December Solstice||It marks the first day of summer.||It marks the first day of winter.|
March Equinox – First Day of Autumn in Southern Hemisphere
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 the 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 the march equinox, the sun switches sides 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 the September equinox, the sun switches sides from the northern hemisphere to the southern hemisphere of the earth. That’s why the September equinox is also known as the Southward Equinox.
March Equinox – Northward Equinox
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 a proper understanding.
Hence, marking the end of the summers and the start of autumn in the southern hemisphere. That’s why the march equinox aka northward equinox is officially known as the autumn equinox in the southern 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 winter 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 equinox in the northern parts of the earth.
Equal Day and Night
Yup, you heard me right. We have equal day and night during the march equinox (also during the 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 Spring and Autumn Equinox, the length of day and night becomes equal.
Shorter Days Longer Nights
There are two ways to practically observe the arrival 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, can’t go unnoticed. Second, You can notice that the days are getting shorter and the nights are getting longer.
In other words, after the Fall equinox 2023, 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 and longer nights will go on until the arrival of the June solstice.
Autumn Equinox – First Day of Autumn or Mid-Autumn?
Now is the time we should talk about the meteorological definition of the autumn equinox. Well, technically speaking, if we go by the meteorological definition, it marks the end of half of the fall or autumn season i.e mid-autumn.
However, on the other hand, if we go by the astronomical definition, 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 eye, which is in fact in the modern notation known as the meteorological definition of autumn equinox or simply meteorological autumn.
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
|Seasons||Meteorological Season Dates||Astronimocal Season Dates|
|Autumn Equinox||Tuesday, 1 March 2023||Tuesday, 21 March 2023|
|Winter Solstice||Wednesday, 1 June 2023||Thursday, 22 June 2023|
|Spring Equinox||Thursday, 1 September 2023||Saturday, 23 September 2023|
|Summer Solstice||Thursday, 1 December 2023||Friday, 22 December 2023|
When is the First Day of Autumn 2023 in Southern Hemisphere?
In 2023, Autumn Equinox in Australia (southern hemisphere) will occur on Tue, March 21, at sharp 08:25 AEDT (Australian Eastern Daylight Time). 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.
Well, yeah, for European people, it will be the spring equinox. I hope you know the exact reason behind it.
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