Equinox vs Solstice – What’s the Difference?

There are generally four seasons that occur on earth due to the occurrence of equinoxes and solstices. On the other hand, the equinox and solstice occur due to the ever-changing position of the earth with respect to the sun.

In other words, the four seasons of the earth take place because of the earth’s changing position with respect to the sun. The spring and autumn occur due to equinoxes. On the other hand, the summer and winter occur due to the solstices.

Not to mention, there is one more important factor that majorly contributes to the occurrence of the seasons on earth. But, we will talk about it in the later section. So, without wasting any more time, let’s come back to the topic of the discussion i.e what is the difference between equinox and solstice?

The primary difference between equinox and solstice is that equinox is a day when daylight and night-time become equal. On the other hand, a solstice is a day either having the longest or the shortest day of the year.

As a matter of fact, in this exclusive article, I am going to get you through each and every detail regarding these two. But, before going into the deep discussion, let me give you a brief review of the two in a tabular form. Let’s dive right in!!!

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Equinox vs Solstice

 EquinoxSolstice
1.An Equinox is a day when daylight and night-time become equal.A Solstice is a day either having the longest or the shortest day of the year.
2.There are two types of equinoxes i.e spring and autumn equinox.There are two types of solstice i.e summer and winter solstice.
3.Spring and Autumn (Fall) equinox mark the arrival of the first day of spring and autumn.Summer and winter solstice marks the arrival of the first day of summer and winter.
4.On the eve of the equinox, the sun crosses over the celestial equatorial line of the earth.On the eve of the solstice, one of the poles is at the maximum tilt away from or towards the sun.
5.An equinox occurs once in March and once in September.A solstice occurs once in June and once in December.
6.Just because of the earth’s tilt, in the month of March, when there is a spring equinox in the northern hemisphere. At the same time, there is autumn or fall equinox in the southern hemisphere.Just because of the earth’s tilt, in the month of June, when there is summer solstice in the northern hemisphere. At the same time, there is winter solstice in the southern hemisphere.
7.Just because of the earth’s tilt, in the month of September, when there is an autumn equinox in the northern hemisphere. At the same time, there is a spring equinox in the southern hemisphere.Just because of the earth’s tilt, in the month of December, when there is the winter solstice in the northern hemisphere. At the same time, there is the summer solstice in the southern hemisphere.
From the above-given equinox and solstice difference in tabular form, you got the exact overview of these two. However, let us try to understand both of them in a detailed format. Keep reading!

 

Thanx to Earth’s Tilt, We See Equinoxes and Solstices

Yup, you heard me right! Thanx to the earth’s tilt we see Equinox and Solstice too. Just because the earth has an axial tilt of 23.4 degrees, there is a seasonal difference between the northern and the southern hemisphere.

due-to-earths-tilt-equinox-and-solstice-occurs
Image Credit: Merriam-Webster Inc.

Suppose if the axis of the earth was not tilted like it is currently, there would be no seasons on the earth. In other words, in a given location, there would always be the presence of direct sunlight. On the other hand, at some other location, there would always be the presence of darkness throughout the years.

Not to mention, Kepler’s laws of planetary motion also play an important role in the occurrence of different seasons. But the role played by the earth’s tilt is unmatchable. To summarize, I would say that without the earth’s tilt, there would be no occurrence of Equinoxes as well as the solstices too.

 

What is an Equinox?

According to the astronomical definition of an equinox, this is a natural event during which the center of the sun crosses 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.

What does equinox mean?

The word “Equinox” is derived from the Latin word “Aequinoctium”. Confused?? Okay. Let me simplify it for you. The word “Aequinoctium” is made by combining two words i.e “Aequus” and “Nox”.

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

“Aequus” means “Equal” and “Nox” means “Night”. Therefore, “Aequinoctium” simply means “Equal Night”. That’s why Equinox is also referred to as a day when daylight and night-time become equal.

 

Types of Equinox

There are two types of equinoxes. These are spring and fall equinoxes. In reality, these are astronomical types of equinoxes. I mean these names are given according to the astronomical definition of seasons that occurs during the time of equinoxes in one of the hemisphere.

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

However, the official names of Equinoxes are somehow different from the above-mentioned ones. Confused? Okay. Let me sort it out for you. According to the definition of an equinox, the two types of equinoxes are March and September Equinox.

March Equinox aka Northward Equinox

On the eve of the March Equinox, the sun crosses over the imaginary celestial line from the south to the north direction. Therefore, as a result, marking the end of winters and the arrival of spring in the northern hemisphere.

That’s why March equinox is officially known as Spring or simply Vernal Equinox in the northern hemisphere. Not to mention, just because the sun crosses over the imaginary celestial line from the south to the north direction, March Equinox is also known as the Northward Equinox.

Moving ahead, as the sun switches side from south to north, March Equinox marks the end of summers and the arrival of fall in the southern hemisphere. Hence, known as the fall or autumn equinox.

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September Equinox aka Southward Equinox

On the eve of September Equinox, the sun crosses over the imaginary celestial line from the north to the south direction. Therefore, as a result, marking the end of summers and the arrival of fall in the northern hemisphere.

That’s why September Equinox is officially known as the Fall or simply Autumn Equinox in the northern hemisphere. Not to mention, just because the sun crosses over the imaginary celestial line from the north to south direction, September Equinox is also known as the Southward Equinox.

Moving ahead, as the sun switches side from the north to south, September Equinox marks the end of winters and the arrival of spring in the southern hemisphere. Hence, known as the spring or Vernal Equinox in the southern hemisphere.

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When is the first day of spring?

As you already know that just because of the earth’s tilt, when there is a spring equinox in the northern hemisphere, there is a fall equinox in the southern hemisphere. Therefore, I am not going to explain it again.

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

Moving ahead, as of today, in the northern hemisphere, the first day of spring will occur on Saturday, March 20, 2021, at sharp 5:37 Eastern Daylight Time (EDT).

On the other hand, in the southern hemisphere, the first day of spring will occur on Thursday, September 23, 2021, at sharp 5:21 Australian Eastern Daylight Time (AEDT).

Must Read: March Equinox 2021 – First Day of Spring in Northern Hemisphere

When is the first day of fall?

As of today, in the northern hemisphere, the first day of fall will occur on Wednesday, September 22, 2021, at sharp 14:21 Eastern Daylight Time (EDT).

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

On the other hand, in the southern hemisphere, the first day of fall will occur on Saturday, March 20, at sharp 21:37 Australian Eastern Daylight Time (AEDT).

Check Out: March Equinox 2021 – First Day of Fall in Southern Hemisphere

 

What is a Solstice?

According to the astronomical definition of solstices, this is a natural event during which one of the hemispheres is at the maximum tilt away from or towards the sun.

And, when this happens, the sun appears to stand still and reverses its direction. In other words, Solstice is a day that occurs due to the sun’s changing path.

What does solstice mean?

The word “Solstice” is derived from the Latin word “Solsistere”. Confused?? Okay. Let me simplify it for you. The word “Solsistere” is made by combining two words i.e “Sol” and “Sistere”.

“Sol” means “Sun” and “Sistere” means “to standstill”. Therefore, “Solsistere” simply means “a day when the sun stands still”.

 

Types of Solstices

There are two types of solstices. These are summer and winter solstices. In reality, these are astronomical types of solstices. I mean these names are given according to the astronomical definition of the seasons that occurs during the time of solstices in one of the hemisphere.

However, the official names of Solstices are somehow different from the above-mentioned ones. Confused? Okay. Let me sort it out for you. According to the definition of Solstice, the two types of solstices are June and December Solstice.

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June Solstice

On the eve of June Solstice, the north pole of the earth is at its maximum tilt towards the sun. Therefore, as a result, marking the end of spring and the arrival of summer in the northern hemisphere.

That’s why June Solstice is officially known as Summer or simply Estival Solstice in the northern hemisphere. Not to mention, not only the Sun’s orbital path across the sky will be as high as it can be in the earth’s northern areas. The sun will also enter the tropic of Cancer on the eve of June Soltice.

earth's-maximum-tilt-during-june-solstice
At the June solstice, the subsolar point is further north than any other time: at latitude 23.44° north, known as the Tropic of Cancer. Image Credit: Wikimedia Commons

Moving ahead, as the Earth’s north pole is tilted closest to the Sun, June Solstice marks the end of autumn and the arrival of winters in the southern hemisphere. Hence, known as the winter or hibernal solstice in the southern hemisphere.

Additionally, the day of June solstice will be the brightest as well as the longest day of the year in the northern hemisphere. On the contrary, it will also be the darkest as well as the shortest day of the year in the southern hemisphere.

December Solstice

On the eve of December Solstice, the south pole of the earth is at its maximum tilt towards the sun. Therefore, as a result, marking the end of spring and the arrival of summer in the southern hemisphere.

That’s why December Solstice is officially known as Summer or Estival Solstice in the southern hemisphere. Not to mention, not only the sun’s orbital path across the sky will be as high as it can be in the earth’s southern areas. The sun will also enter the tropic of Capricorn on the eve of December Solstice.

earth's-maximum-tilt-during-december-solstice
At the December solstice, the subsolar point is further south than any other time: at latitude 23.44° south, known as the Tropic of Capricorn. Image Credit: Wikimedia Commons

Moving ahead, as the earth’s south pole is tilted closest to the Sun, the December solstice marks the end of autumn and the arrival of winters in the northern hemisphere. Hence, known as the winter or hibernal solstice in the northern hemisphere.

Additionally, the day of December solstice will be the brightest as well as the longest day of the year in the southern hemisphere. On the contrary, it will also be the darkest as well as the shortest day of the year in the northern hemisphere.

 

When is the first day of summer?

Again, you already know that because of the earth’s axial tilt, when there is the summer solstice in the northern hemisphere, there is the winter solstice in the southern hemisphere.

first-day-of-summer
An image of the first day of the summer during the Shimla Summer Festival. Image Credit: TravelTriangle

Therefore, moving ahead, as of today, in the northern hemisphere, the first day of summer will occur on Sunday, June 20, 2021, at sharp 23:32 Eastern Daylight Time (EDT).

On the other hand, the first day of summer in the southern hemisphere will occur on Wednesday, December 22, 2021, at sharp 2:59 Australian Eastern Daylight Time (AEDT).

Take a look at: December Solstice: First Day of Summer in Southern Hemisphere

When is the first day of winter?

As of today, the first day of winter in the northern hemisphere will occur on Tuesday, December 2021, at sharp 10:59 Eastern Daylight Time (EDT).

first-day-of-winter
An image of the first day of the winters from the Indian remote village of Malana, Himachal Pradesh. Image Credit: Mint

On the other hand, the first day of winter in the southern hemisphere will occur on Monday, June 21, 2021, at sharp 15:32 Australian Eastern Daylight Time (AEDT).

 Highly Recommended: December Solstice: First Day of Winter in Northern Hemisphere

Why do the dates of the solstices and equinoxes vary?

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 next year i.e 2020, it occurred on 21th of the month. Such is the case with all the types of Equinox and Solstice.

Not to mention, there are some other factors too, that contribute to the variation in the equinox and solstice dates. But, just to make things simple, I am just neglecting them.

At last, 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.

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