Difference Between Equinox and Solstice.
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.
Similarly,
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.
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.
Solstice is a
day either having the longest or the shortest day of the year.
A brief review
of the two in a tabular form.
An Equinox is a
day when daylight and night-time become equal.
There are two
types of equinoxes i.e. spring and autumn equinox.
Spring and Autumn
(Fall) equinox mark the arrival of the first day of spring and autumn.
On the eve of
the equinox, the sun crosses over the celestial equatorial line of the earth.
An equinox
occurs once in March and once in September.
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
September, when there is an autumn equinox in the northern hemisphere. At the
same time, there is a spring equinox in the southern hemisphere.
A Solstice is a
day either having the longest or the shortest day of the year.
There are two
types of solstice i.e. summer and winter solstice.
Summer and
winter solstice marks the arrival of the first day of summer and winter.
On the eve of
the solstice, one of the poles is at the maximum tilt away from or towards the
sun.
A solstice
occurs once in June and once in December.
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.
Just because of
the earth’s tilt,
in the month of
December, when there is winter solstice in the northern hemisphere. At the same
time, there is summer solstice in the southern hemisphere.
Understand both
of them in a detailed format.
Due 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.
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 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”.
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. According to the definition of Solstice, the two types of solstices are
June and December Solstice.
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.
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.
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.
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.
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 sides from
one hemisphere of the earth to the other.
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”.
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.
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.
However, the
official names of Equinoxes are somehow different from the above-mentioned
ones. According to the definition of an equinox, the two types of equinoxes are
March and September 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 sides 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.
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 sides from the north to the 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.
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.
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.
From. Atul
Sinha
A mechanical
engineer by profession.
A postgraduate
degree in physics.
Undergoing Ph.D.
in theoretical physics, especially in the field of cosmology.
(He is of the view
that, every aspect of physics comes within the range of cosmology. )
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