What is Equinox: Types, Dates, Diagram,and Solstice

Have you ever heard of the equinox? It’s a time of year that has special significance for many people. But what is it, exactly? And why is it so important? Here’s a closer look at this fascinating phenomenon.

Solar equinoxes occur when the Sun’s center is directly over the equator, and its rays are perpendicular to the Earth’s surface. They also mark the beginning of Spring and Autumn in the northern hemisphere (and summer/winter in the southern hemisphere).

At the equinoxes, the day and night are each exactly 12 hours long, measured at any point equidistant from the equator. Each equinox is accompanied by an equinoxal moon, a full Moon that occurs with the Sun at 180°.

What is Equinox

A fancy word for “equal night,” an equinox is when the sun crosses our Earth’s equator. This happens twice a year when the tilt of the Earth’s axis is perpendicular to the sun’s rays. In Latin, the word aequinoctium refers to an equal night, derived from the words aequus (equal) and nox (night).

Since Earth’s orbit deviates slightly from a perfect ellipse due to the moon, the equinox is now determined by the sun’s ecliptic longitude rather than its declination. The equinoxes are currently defined as the points in time when the sun’s apparent geocentric longitude is 0° and 180°.

Types of Equinoxes

There are two types of equinoxes – the Vernal Equinox and the Autumnal Equinox. The Vernal Equinox marks the first day of Spring in the northern hemisphere, while the Autumnal Equinox falls on September 23 and is considered the first day of Fall. 

In this day’s solar cycle, the sun rises due east and sets due west everywhere, except for the extreme north or south latitudes.

Vernal or Spring Equinox

During March, the Northern Hemisphere experiences the vernal equinox, while September is autumnal or fall equinox. In the Southern Hemisphere, this is the opposite. 

Vernal or Spring Equinox is the moment when the sun crosses the celestial equator from South to North. It occurs on March 20th or 21st of every year. This event marks the beginning of astronomical spring in the Northern Hemisphere and autumn in the Southern Hemisphere. 

Vernal Equinox is the time when day and night are equal in length. From this day onwards, the days start getting longer in the Northern Hemisphere and shorter in the Southern Hemisphere.

Vernal or Spring Equinox has been celebrated since ancient times. It was a special occasion for many cultures around the world. The ancient Egyptians, for instance, built the Great Sphinx of Giza, aligning it precisely on the vernal equinox day. 

Many ancient cultures saw this event as a time of rebirth and rejuvenation. In modern times, people continue to celebrate Vernal or Spring Equinox as a time of new beginnings. For many, it is a time to plant gardens, start new projects, or enjoy the warmer weather.

Whether you celebrate Vernal or Spring Equinox with a special ceremony or take a moment to appreciate the changing seasons, this astronomical event will surely fill you with a sense of wonder and anticipation for the months ahead.

March Equinox 2023

Northern Hemisphere spring begins with the March equinox, while in the Southern Hemisphere, it marks the start of autumn. On March 20, 2023, the March equinox will occur at 21:25 UTC.

As you move south of the equator, you’ll find the opposite season – later sunrises, earlier sunsets, chillier winds, and falling leaves.

• Signs of the March Equinox in Nature

Around the globe, the equinox brings us many seasonal effects that are noticeable to nature lovers. Early morning sunrises, late evening sunsets, and sprouting plants are all signs of the March equinox.

Don’t forget to observe the path of the sun every day. You will notice that it has shifted northward. Similarly, birds and butterflies are migrating back northward in response to the changes in daylight.

In many parts of the world, spring flowers are beginning to bloom as the days lengthen. As daylight hours increase, the weather becomes warmer. Winter coats are being left at home. The trees are budding, and the plants are starting to grow again.

March Equinox Dates

Year	Spring Equinox (Northern Hemisphere)	Spring Equinox (Southern Hemisphere)
2022	Sunday, March 20	Thursday, September 22
2023	Sunday, March 20	Friday, September 23
2024	Saturday, March 19	Thursday, September 22
2025	Sunday, March 20	Thursday, September 22

2. Autumnal or Fall Equinox

Autumnal Equinox falls on September 23 and is considered the first day of Fall. The Autumnal or Fall Equinox is the perfect time to celebrate the bounty of the harvest season. From delicious fruits and vegetables to cozy sweaters and crisp autumn air, there is so much to enjoy about this time of year.

For many, the Autumnal Equinox also marks the start of a new school year. Whether starting a new grade or heading off to college, this time of year can be filled with excitement and anticipation.

No matter your plans for the Autumnal Equinox, take some time to enjoy the simple things in life. Spend time with family and friends, savor the season’s flavors, and take in all the beauty that autumn offers.

Equinoxes alternate with solstices throughout the year. Due to leap years and other factors, the dates of both events may vary slightly.

September Equinox 2022

The September Equinox also called the Autumnal or Fall Equinox, marks the start of fall in the Northern Hemisphere. It is anticipated that the next September equinox will occur on September 23, 2022, at 1:04 UTC. 

In the Northern Hemisphere, this is the start of fall, and in the Southern Hemisphere, it is the beginning of spring. The autumnal equinox occurs when the sun’s path across the sky is almost directly from south to north.

Signs of the September Equinox in Nature

For several nights, the full moon rises around sunset. This traditionally provides farmers with sufficient light to complete their harvests before the killing frosts of fall begin.

At night, the moon rises about an hour later. However, during the fall equinox, the angle of the moon’s orbit and the tilt of the Earth coincide perfectly. This causes the moon to rise approximately 20 to 30 minutes later each night for several nights consecutively.

Autumnal Equinox Dates

Year	Autumnal Equinox (Northern Hemisphere)	Autumnal Equinox (Southern Hemisphere)
2022	Thursday, September 22	Sunday, March 20
2023	Friday, September 23	Sunday, March 20
2024	Thursday, September 22	Saturday, March 19
2025	Thursday, September 22	Sunday, March 20

Equinox Diagram

What is Solstice

In Latin, solstice refers to the remaining of the sun; thus, it means “the sun must stand still”. The word solstice (combines the Latin words sol for “Sun” and sistere for “To Stand Still.” This is because the sun appears to stop moving north or south for three days.

On a Solstice, the Earth tilts toward or away from the sun. This means that one side of Earth will face the sun, while the other will be facing away from it. Solstices occur twice yearly: once in winter (December 21-22) and once in summer (June 21-22). 

The result is longer days for those who live on the side facing the sun and shorter days for those who live on the side facing away from it.

Solstices in the Northern and Southern Hemisphere

Solstices occur when Earth’s axis is tilted 23 degrees relative to its orbital plane around the Sun. During the winter solstice, Earth’s Northern Hemisphere is tilted away from the Sun; during the summer solstice, Earth’s Southern Hemisphere is similarly positioned.

As a result of this tilt, both hemispheres receive more direct sunlight than if they were perpendicular to their orbital plane around our star (which would be 0 degrees).

During the June solstice, the North Pole is tilted closest to the Sun, and the Sun’s rays directly illuminate the Tropic of Cancer, which marks the start of summer in the Northern Hemisphere. 

Winter begins on the December solstice when the South Pole is closest to the Sun, and the Sun’s rays are directly overhead at the Tropic of Capricorn. (The seasons are reversed in the Southern Hemisphere.)

Difference Between Solstice and Equinox

Solstice and equinox are two astronomical events that occur during the year. Solstices happen twice a year and mark the changing seasons, while equinoxes occur twice yearly: once in spring (March 20-21) and once in autumn (September 22-23). 

The date for both of these can vary depending on where you live in the world, but generally speaking, Solstices occur in December and June, while Equinoxes occur around March and September.

Equinoxes differ from solstices because a solstice is the longest or shortest day of the year, while an equinox is when the day and night are equal in length.

Does Equinox Has Any Effect on Seasons

As the Earth travels around the Sun, its axis is slightly tilted, so different points receive varying amounts of sunlight during different seasons. 

If Earth were not tilted, the Sun would always appear directly above the Equator, the amount of light received by a given location would be fixed, and seasons wouldn’t exist.

Seasons are not affected by the Earth’s distance from the Sun.  In this scenario, it would be hotter in the northern hemisphere during January than it would be during July in the northern hemisphere.

A typical tilt on the Earth’s axis is 23.5 degrees, which is the reason for the seasons (the tilt varies between 22 and 25 degrees).

In the northern hemisphere, sunlight has a more direct path to the ground due to its shorter travel distance through the atmosphere.

Less sunlight gets scattered before it reaches the ground. As a result of the high sun angle, days in the southern hemisphere are short, whereas in the northern hemisphere, they are long.

Sun’s rays are affected by Earth’s rotation on its N-S axis, which is tilted away from the sun’s axis throughout the year. 

As a result,  the Sun’s energy has to travel through more of the atmosphere before reaching the ground. Winter solstice occurs in the southern hemisphere around the 21st of June.

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