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What’s the Difference Between a Solstice and an Equinox?

Written by Saanchi Biyani, a grade 5 student.

Both have something to do with the earth’s relation to the Sun’s path. But, what do they mean?

By I Kid You Not , in Current Stories Did You Know Science What's the Difference Between , at June 5, 2021 Tags: , , ,

Written by Saanchi Biyani, a grade 5 student.

First, here’s what they both mean – and you’ll see the difference. You’ll see that the difference lies in their very definitions. Both are periodic solar events that happen on the same date every year.

What’s the difference between a Solstice and an Equinox?

The Solstice – either of the two times in a year when the Sun’s path is as far north or as far south from the Earth’s Equator. This is marked by the longest and shortest days in the year (about 21 June and 22 December).

The Equinox – either of the two times in a year when the Sun is right above the Equator and day and night are of equal length.  The equinoxes happen twice a year– once on 21 March and once on 23 September.

Have you ever wondered why is there more daylight in summer than in winter? You would have seen a lot of different kinds of seasons in a year – have you ever thought about why seasons change?

Have you ever thought if we have a signal for the change in seasons? To understand all this, one needs to understand the Earth’s orbit and how it functions.

Similarly, the equinoxes and solstices are dependent on the Earth’s revolution around the sun.

Let me explain it further…

The Earth moves in two ways – rotation and revolving – here’s what the two mean


The Earth rotates around its axis, spinning like a top. Like this:

It is believed that the rotation is caused by the Earth’s magnetic field. One rotation is completed in 24 hours, which is one day for us.

But, here’s the interesting part – the inclination (angle or slant) of the Earth’s axis is important to understand.

Earth’s Axis

The Earth’s axis is an imaginary line that runs between the north and south poles.

This axis is not straight, it’s inclined at 23.5 degrees. And this tilting of the axis causes a difference in the amount and kind of sunlight Earth receives over its entire surface area.

The tilt leads to some areas around latitudes like the Equator and the Tropics of Cancer and Capricorn to receive more sunlight. Areas around the latitudes of the Arctic Circle etc receive lesser sunlight.


While busy in turning daily circles, the Earth is also traveling around the Sun, which is known as Earth’s orbit. It takes 365 and ¼ days for the Earth to make one complete trip around the Sun, which, we define as a year.

Revolution is, in a sense, a larger motion. The Earth revolves around the sun in an elliptical orbit (oval) – a motion most celestial bodies, like planets have because of the gravitational force.

Earth’s revolution is what causes seasons. The seasonal cycle of spring, summer, monsoon, and winter we all enjoy is because of the Earth spinning around the sun. Yet, not all places get these four seasons. The amount of sunlight these places receive varies with the Earth’s axial tilt.

Again, the axis tilt of the earth is what’s important

The Earth is slightly tilted while it orbits around the Sun, which means, it is slightly pointed towards or away from the Sun.

Depending on your location on Earth, there are times your half of the world, known as the hemisphere, is pointed toward the Sun, while, at other times, it is pointed away from the Sun.

As the tilt of Earth’s axis points one’s hemisphere towards or away from the Sun, we experience the changing of the seasons. If it weren’t tilted, we wouldn’t have had seasons – only areas that were colder (near the poles) and warmer (near the Equator).

How does this cause solstices and equinoxes?

The axial tilt of the Earth ensures that different places receive different amounts of sunlight. On Earth, solstices are caused by solar declination. 

Solar declination indicates the latitude over which the sun is directly overhead at noon. The closer you are to the Equator, the more sunlight you receive, and the warmer it is. The closer you are to the Poles, the lesser sunlight you receive, and the colder it is.

So, the occurrence of the solstices and the equinoxes depends on the tilt of the Earth’s axis, the incident solar energy, and the latitude of a place. They are defined by the Earth’s position in its orbit relative to the sun.

How are they different?

A solstice marks either the shortest or longest day of the year. An equinox marks the happening of equal day and night.

During solstices, the sun moves (appears to move, for it is the Earth that is actually moving) farthest north or south from the Equator.

During equinoxes, the sun shines directly over the Equator.

Solstices mark the beginning of summer (the sun shines over the Tropic of Cancer in June– this means that the Northern Hemisphere is experiencing summer while the Southern Hemisphere is experiencing winter) and winter (the sun shines over the Tropic of Capricorn in December– this means that the Southern Hemisphere is experiencing summer while the Northern Hemisphere is experiencing winter).

The Equinoxes mark the beginning of spring (the vernal equinox in March) and autumn (the autumnal equinox in September).

Solstice and Equinox mark the change in seasons. But do you know which represents what change? Read on..

The two solstices happen in June (20 or 21) and December (21 or 22).

June 21/22 is the longest day, while 21/22 December is the shortest day in the year. In the solstices, the Earth’s poles are the farthest from the Sun.  In the Northern hemisphere, the June solstice marks the start of the summer (the North Pole is tilted closest to the Sun), while, the December solstice marks the start of winter (the South Pole is tilted closest to the Sun).

In the Southern Hemisphere, the seasons are reversed. This is because the South Pole is pointed in a direction opposite to the North Pole. If the North Pole points to the sun, the South Pole points away from the sun, and vice versa

The equinoxes happen in March and September. March 21 and September 23 are the days when the Sun is exactly above the Equator, making day and night of equal length. March equinox marks the start of spring, while, the September equinox marks the start of Autumn.

This is so good to learn. Isn’t it? In fact, I am a firm believer that 95 percent of things have a reason or logic attached to them. It is just 5 percent of the things that come into the category of ‘believe it or not’.

Have you ever wondered why there are only 52 cards in a deck? Why there are 4 suits?

There’s a logic for it.

The 52 cards represent the 52 weeks in a year. The 4 suits represent the 4 seasons in a year. Isn’t this interesting?

Read on…

The 12 faces on a card represent the 12 months, while, the 13 cards in one suit represent the 13 weeks in one season. The story is yet not complete. If you add all the digits (1 to 13) of the cards, multiply by 4 (4 suits), and add 1 (one pack of cards), you will get 365 which is the number that represents the days in a year. Last but not the least, the red cards represent the day, while, the black cards represent night – aren’t both equal in number – like an equinox!

The solstices and equinoxes also play a very important role in tarot card readings. In tarot, it is believed that the positioning of celestial bodies can often predict one’s future.

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