December solstice marks the arrival of the first day of summer in the southern hemisphere. That’s why in the earth’s southern areas, we call it a summer solstice that will occur on Monday, December 21, 2020, at sharp 21:02 Australian Eastern Daylight Time (AEDT). Not to mention, this astronomical event will also be the brightest as well as the longest day of the year in the southern hemisphere.
On the other hand, for the people living in the northern hemisphere, this solstice marks the arrival of the first day of winter. That’s why in the earth’s northern areas, we call it a winter solstice. Again, for the people living in the northern half of the earth, this astronomical event will also be the darkest as well as the shortest day of the year in the northern hemisphere.
Before taking questions like why the south and north solstice mismatch happens. Or, is December solstice i.e a summer solstice is really the official first day of summer in the southern hemisphere, Well, let me tell you some basic physics regarding the current topic. Keep reading.
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What is a Solstice?
According to the astronomical definition of the solstice, this is a naturally occurring event during which the sun appears to stand still and reverses its direction. In other words, you can also think of it as a seasonal shift that occurs due to the sun’s changing path.
Not to mention, there are two types of the solstice that are the winter and summer solstice. The summer solstice, also known as the Estival Solstice that marks the first day of the summer. And the winter solstice, also known as the hibernal solstice that marks the first day of the winter.
Just to let you know, in total, there are generally four seasons that occur on earth. These are summer, winter, autumn, and spring. Just like the summer and winter solstice is responsible for the arrival of summer and winter season.
In a similar fashion, Spring and Autumnal equinox are responsible for the arrival of the first day of the spring and autumn season. 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 here that why we see a mismatch between the south and the north. In other words, why when there is the summer solstice in the southern hemisphere, there is the winter solstice in the northern hemisphere?
Thanx to Earth’s Tilt, we see Solstice & Equinoxes too!
Just because the earth has an axial tilt of 23.4 degrees, there is a mismatch between the southern and the northern hemisphere. (Don’t worry, we will talk about it in the later section in detail).
In other words, you can say that the earth’s axial tilt plays a major role in the formation of seasons around the globe. To understand it properly, refer to the above image. Additionally, check the below table to understand different solstice in different hemispheres.
Basic Difference Because of Earth’s Tilt
|Basis of Comparision||Southern Hemisphere||Northern Hemisphere|
|March Equinox||In the southern hemisphere, it marks the arrival of autumn, therefore, Autumn Equinox.||In the northern hemisphere, it marks the arrival of spring, therefore, Spring Equinox.|
|June Solstice||It marks the arrival of winter, therefore, Winter Equinox.||It marks the arrival of summer, therefore, Summer Solstice.|
|September Equinox||Marks the arrival of spring, therefore, the Spring Equinox.||Marks the arrival of autumn, therefore, Autumn Equinox.|
|December Equinox||It marks the arrival of summer, therefore, Summer Equinox.||It marks the arrival of winter, therefore, Winter Equinox.|
From the above comparison chart, it is clear that the solstice that occurs in December in the southern hemisphere is the Summer solstice. On the other hand, the solstice that occurs in December in the northern hemisphere is the winter solstice.
December Solstice: First Day of Summer in Southern Hemisphere
The December solstice marks the arrival of summer in the southern hemisphere. Just because of the tilt of the earth, on the eve of the summer solstice, half of the earth’s surface (southern hemisphere) receives the maximum sunlight.
WHY? Because the southern hemisphere is at the maximum tilt towards the sun, hence becomes the brightest day of the year. In fact, you can also think of this astronomical event as the day when the sun stands still for a moment and reverses its direction of motion.
Additionally, during the summer solstice in the southern hemisphere, not only the sun’s orbital path across the sky is as high in the sky as it can be. The sun will also enter the tropic of Capricorn on the day of the December solstice.
And, with that, the days get shorter after the summer solstice. That’s why the summer solstice in the southern hemisphere is also known as the midsummer.
Summer Solstice: First Day of Summer or Midsummer?
Well, if we go by the meteorological definition of the summer solstice, it marks the end of the half of the summer season i.e midsummer.
On the contrary, if we go by the astronomical definition of the summer solstice, it marks the arrival of the first day of the summer.
Therefore, the question arises here, why we have two different definitions for a single event. Most importantly, which one of these is the correct one? Let’s find out.
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Let’s go back in time!
Before the arrival of the scientific revolution, humans didn’t know how to calculate the change in the seasons 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 summer solstice or simply meteorological summers.
On the other hand, what our astronomers and scientists calculate with their super-sophisticated technology is defined as the astronomical definition of the summer solstice or simply astronomical summers.
Therefore, to conclude, I would say that both definitions are correct in their own sense. Hence, as a result, some people define the summer solstice in the southern hemisphere as the first day of the summer. On the contrary, some people define it as the end of the half of the summer season, hence midsummer.
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|
|Autumn||Sunday, March 1, 2020||Thursday, March 19, 2020|
|Winter||Monday, June 1, 2020||Saturday, June 20, 2020|
|Spring||Tuesday, September 1, 2020||Tuesday, September 22, 2020|
|Summer||Tuesday, December 1, 2020||Monday, December 21, 2020|
What is the first day of summer in the southern hemisphere?
The first day of summer in the southern hemisphere will happen on Monday, December 21, at sharp 21:02 Australian Eastern Daylight Time (AEDT). It is the time when the sun will be at the highest elevation in the sky. Therefore, as a result, marking the longest day of the year in the southern hemisphere.
Well, not just the longest, it will also be the brightest as well as the shortest night of the year in the earth’s southern hemisphere.
Not to mention, this astronomical event will occur at the same moment for all of us. In other words, whether you are living in Capetown or in Sydney or even in London (i.e in the northern hemisphere), it will be a moment of joy for all of us at the same instant.
Well, the only difference will be that the people in the southern hemisphere will be celebrating the summer solstice. On the other hand, the people living in the northern hemisphere will be celebrating the winter solstice.
Why the summer solstice date varies?
Yup, you heard me right. The summer solstice date does vary. See, after every four years, there is a leap year. Therefore, in order to adjust the solar calendar (Gregorian Calendar) with the eve of the summer solstice, the December solstice date varies.
For example, in 2019, the summer solstice in the southern hemisphere occurred on the 22nd of December month. But this year i.e 2020, it will occur on the 21st of December month.
Not to mention, there are some other factors too, that contribute to the variation in the dates of the summer solstice. But, just to make things simple, I am just neglecting them.
How Long is the Longest Day of the year?
Well, how long is the longest day of the year in the southern hemisphere simply depend on the fact that how close you are residing towards the south pole.
In other words, the more closer you reside in the southern hemisphere to the south of the antarctic circle towards the south pole, the more hours of daylight you will receive.
According to the data released by the Finnish Meteorological Institute, during the 2015 summer solstice of the southern hemisphere, the exact south pole received 24 hours of daylight. Similarly, Johannesburg received approximately 13 hours and 47 minutes of daylight.
Capetown received 14 hours and 25 minutes of daylight. The city of Invercargill of New Zealand received 15 hours and 48 minutes of daylight. The city of Ushuaia of Argentia received 17 hours and 19 minutes of daylight.
Not to mention, if we talk about the whole of the southern hemisphere as one, the longest day of the year in the southern hemisphere received an average of 15 hours of daylight. Don’t forget, the closer you are to the south pole, the maximum hours of daylight you will receive.