December solstice marks the arrival of the first day of winter in the northern hemisphere. That’s why in the earth’s northern areas, we call it a winter solstice that will occur on Monday, December 21, 2020, at sharp 10:02 (UTC). Not to mention, this astronomical event will also be the darkest as well as the shortest day of the year in the northern hemisphere.
On the other hand, for the people living in the southern hemisphere, this solstice marks the arrival of the first day of summer. That’s why in the earth’s southern areas, we call it a summer solstice. Again, for the people living in the southern half of the earth, this astronomical event will also be the brightest as well as the longest day of the year in the southern hemisphere.
Before taking questions like why the north and south solstice mismatch happens. Or, is December solstice i.e a winter solstice is really the official first day of winter in the northern hemisphere, well, let me tell you some basics 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 solstice. These are winter solstice and summer solstice. A winter solstice, also known as the hibernal solstice marks the official first day of the winter. And the summer solstice, also known as the Estival solstice marks the official first day of summer.
Just to let you know, in total, there are typically four seasons that occur on earth. These are summer, winter, autumn, and spring. Just like winter and summer solstice is responsible for the arrival of winter and summer season. In a similar fashion, Spring and Autumnal equinox are responsible for the arrival of the first day of the spring and autumn season.
Take a look at March Equinox – First Day of Spring in Northern Hemisphere
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 winter solstice in the northern hemisphere, there is the summer solstice in the southern hemisphere?
Thnx to Earth’s Tilt, we See Solstices & Equinoxes too!
Just because the earth has an axial tilt of 23.4 degrees, there is a mismatch between the northern and the southern hemisphere. Not to mention, Kepler’s law too plays an important role in the formation of different seasons in places above and below the equator. Okay, not that much role as compared to the role played by the tilt of the earth.
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||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 solstice that occurs in December in the northern hemisphere is the winter solstice. On the other hand, the solstice that occurs in December in the southern hemisphere is the Summer solstice.
December Solstice: First Day of Winter in Northern Hemisphere
The December solstice marks the arrival of winter in the northern hemisphere. Just because of the tilt of the earth, on the eve of the winter solstice, half of the earth’s surface (northern hemisphere) receives the minimum sunlight.
WHY? Because the northern hemisphere is at the maximum tilt away from the sun, hence becomes the darkest day of the year. 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 winter solstice in the northern hemisphere, not only the Sun’s orbital path across the sky is as low in the sky as it can be. The sun will also enter the tropic of Capricorn on the eve of the December solstice.
And with that, days get longer after the winter solstice. That’s why the winter solstice in the northern hemisphere is also known as the midwinter.
Winter Solstice: First Day of Winter or Midwinter?
Well, technically speaking, if we go by the meteorological definition of the winter solstice, it marks the end of the half of the winter season i.e midwinter.
However, on the other hand, if we go by the astronomical definition of the winter solstice, it marks the arrival of the first day of the winter. Therefore, the question arises as, why we have two different definitions for a single event. Moreover, 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 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 winter solstice or simply meteorological winters.
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On the other hand, what our astronomers and scientists calculate with their super-sophisticated technology is defined as the astronomical definition of winter solstice or simply astronomical winters.
Therefore, to conclude, I would say that both definitions are correct in their own sense. Hence, as a result, some people define the winter solstice in the northern hemisphere as the first day of the winter.
On the contrary, some people define it as the end of the half of the winter season, hence midwinters. 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||Sunday, March 1, 2020||Thursday, March 19, 2020|
|Summer||Monday, June 1, 2020||Saturday, June 20, 2020|
|Autumn||Tuesday, September 1, 2020||Tuesday, September 22, 2020|
|Winter||Tuesday, December 1, 2020||Monday, December 21, 2020|
When is the Winter Solstice in the Northern Hemisphere?
This year’s winter solstice will happen on Monday, December 21, at sharp 10:02 (UTC). It is the time when the sun will be the lowest in the sky. Therefore, as a result, marking the shortest day of the year in the northern hemisphere.
Well, not just the shortest, it will be the darkest as well as the longest night of the year in the earth’s northern 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 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.
Take a look at March Equinox – First Day of Fall in Southern Hemisphere
Why the winter solstice date varies?
Yes, its date does vary. Well, it’s not rocket science to understand, just some basic physics. See, after every four years, there is a leap year. Therefore, in order to adjust the Gregorian Calendar with the eve of the winter solstice, the December solstice date varies.
For example, in 2019, the December solstice occurred on the 22nd of the month. But this year i.e 2020, it will occur on 21th of the month.
Take a look at: Equinox vs Solstice – What’s the Difference?
Not to mention, there are some other factors too, that contribute to the variation in the dates of the Winter solstice. But, just to make things simple, I am just neglecting them.
How Long is the Shortest Day of the Year?
How long is the shortest day of the year simply depends on the fact how close you are residing to the north pole. In other words, the more closer you reside to the north of the arctic circle towards the north pole, the thinnest hours of daylight you will receive.
According to the data released by the Finnish Meteorological Institute, during the 2015 winter solstice, the Russian port city of Murmansk received zero hours of daylight. Similarly, Copenhagen received approximately 7 hours and 1 minute of daylight.
Rome received 9 hours and 7 minutes of daylight. Los Angeles received 9 hours and 53 minutes of daylight. And, my home i.e New Delhi received 10 hours and 19 minutes of daylight.
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If we talk about the whole of the northern hemisphere as one, the shortest day of the year in the northern hemisphere received an average of 9 hours of daylight. Don’t forget, the closer you are to the north pole, the thinnest hours of daylight you will receive.