The September equinox is coming! For the Northern Hemisphere, it means the summer is over, but in the southern latitudes, the spring just begins. This article explains what an equinox is, how it changes seasons, and when the next equinoxes will be in 2022–2023.
Equinox definition: What is an equinox?
Equinox is a moment of time when the Earth’s axis is tilted neither toward nor away from the Sun, making day and night (almost) equal across the world.
Our planet’s axis of rotation is tilted at 23.5 degrees. This means that the Earth’s Northern and Southern Hemispheres receive unequal amounts of sunlight during most of the year. This axial tilt is the reason we have seasons.
However, two times a year — in March and September — the Earth is positioned so that neither of its hemispheres is inclined towards or away from the Sun. At these instants of time, the Sun is directly above the equator, and both hemispheres receive nearly equal amounts of sunlight. This astronomical event is called an equinox. The equinoxes mark the transition from winter to spring and from summer to fall.
People in the Northern Hemisphere experience the spring (or vernal) equinox in March and the fall (or autumnal) equinox in September. In the Southern Hemisphere, the seasons are reversed. The exact equinox dates vary between March 19 and 21 and September 21 and 24, depending on the year and the time zone.
What happens during an equinox?
At an equinox, people on the Earth experience an almost equal duration of daylight and nighttime — about twelve hours. Why not exactly twelve hours? Theoretically, when the Earth isn’t inclined relative to the Sun, day and night should be equal in length. However, our planet has an atmosphere that refracts light like a prism. When you’re looking at the setting Sun near the horizon, its actual position is about 1.5 degrees lower than what appears to the eye. Atmospheric refraction delays the sunset, which results in more daylight than nighttime on the day of an equinox. At temperate latitudes, this difference equals about eight minutes.
Another interesting phenomenon that occurs at an equinox is the Sun rising due east and setting due west. It’s true for any place on the Earth except for the North and South Poles, where there is no east or west. Here’s why it happens.
No matter where you are, the due east and due west points on your horizon mark the intersection of the celestial equator with the horizon. On the day of an equinox, the Sun is positioned right on the celestial equator. For this reason, the Sun rises due east and sets due west on the day of the equinox all around the globe. So if you want to determine where east and west are in your location, just go outside on the day of the equinox and watch the Sun rise and set.
Equinox dates and times for the Northern Hemisphere
When is the fall equinox 2022?
In 2022, the fall equinox will occur on September 23, at 01:04 GMT (on September 22, at 09:04 EDT). From that moment on, the astronomical autumn will begin.
When is the spring equinox 2023?
The next vernal equinox will occur on March 20, 2023, at 21:25 GMT (5:25 p.m. EDT). This event marks the beginning of the astronomical spring.
Equinox dates and times for the Southern Hemisphere
When is the spring equinox 2022?
The September equinox marks the beginning of spring in the Southern Hemisphere. In 2022, it will be on September 23, at 01:04 GMT (on September 22, at 09:04 EDT).
When is the fall equinox 2023?
The next fall equinox in the Southern Hemisphere is the March equinox in 2023. It will occur on March 20, 2023, at 21:25 GMT (5:25 p.m. EDT). The event marks the beginning of autumn for the southern latitudes.
Harvest Moon & Autumnal equinox
The nearest Full Moon to the autumnal equinox is called the Harvest Moon. In the Northern Hemisphere, it’s usually the September Full Moon, but in some years, it comes in October. The Harvest Moon is particularly kind to the farmers. It gives them more light to finish their harvesting because it rises soon after sunset for the few days around the autumnal equinox. Each day it goes up only 10 to 30 minutes later, unlike the average Moons that rise about 50 minutes later night by night. The reason for this is that the Moon’s orbit is the least tilted to the horizon around the time of the autumnal equinox. Check our article on the Harvest Moon to learn about its date and other peculiarities.
Best time to see the Northern Lights
According to NASA, the weeks around the fall and spring equinoxes are the richest in geomagnetic storms. That means lucky observers from the northern latitudes may spot the aurora borealis or the Northern Lights. The historical records show that geomagnetic storms are twice as likely during spring and autumn compared to summer and winter. So, it’s the best time to await the Northern Lights!
What is the difference between the equinox and solstice?
Both equinoxes and solstices mark the change of seasons, but beyond that, they are opposites:
- Equinox is a time when day and night are almost the same. On the contrary, a solstice leads to the shortest or longest day, depending on the season.
- Equinoxes mark the first days of spring and fall, and solstices mark the beginning of winter or summer.
- On an equinox, the Earth’s axis is tilted neither toward nor away from the Sun, so both hemispheres receive nearly equal amounts of light. On a solstice, one of the Earth’s hemispheres is tilted the most toward the Sun. As a result, one hemisphere experiences the least amount of sunlight while the other enjoys the most of it.
You can learn more about solstices in our article and find the exact date of the next solstice in 2022.
Is the September equinox the first day of fall?
The September equinox is the beginning of the fall in the Northern Hemisphere, which can be between September 21 and 24, depending on the year and your time zone. In the Southern Hemisphere, the fall begins with the March equinox between March 19 and 21.
Is an equinox on the same day everywhere?
In any given year, an equinox happens at the same time all around the globe. However, for people in different time zones, it can happen on different days.
Does an equinox always align with a Full Moon?
These two events are close, but it’s not always a perfect match. The closest Full Moon to the fall equinox is called the Harvest Moon.
Are day and night equal at the equinox?
They are almost equal, but there’s slightly more daylight than nighttime on the day of an equinox. The reason is the atmospheric refraction of sunlight.
Can you balance an egg on the spring equinox?
The short answer is: yes, but it has nothing to do with the equinox. According to a popular myth, on the spring equinox, you can stand an egg on its end due to some gravitational balance between the Earth and the Sun. In reality, there is no gravitational change happening during an equinox that would help an egg balance. And there’s no need for it: you can try this egg-balancing trick any random day of the year. All you need to succeed is a bit of patience.
5 interesting facts about the equinox
- Astronomers in the ancient world chose the vernal equinox as the zero point to measure the movements of stars, and it soon came into use. Already in Julius Caesar’s notes, we see that he planned his sea forays considering the equinox.
- At the equator, the Sun is directly overhead at noon on the days of equinoxes. If you put a vertical stick in the ground at this moment, it will cast no shadow.
- The Earth isn’t the only planet with equinoxes — in fact, every planet with an axial tilt experiences them.
- There are four astronomical dates that mark the beginning of a new season. We already know the first two — the September and the March equinoxes. The other two are the June and the December solstices — the moments when we experience the greatest number of hours of daylight (the June solstice) and the fewest hours of daylight (the December solstice).
- The fastest sunsets are always at the equinoxes, no matter if you live in the Northern or Southern Hemisphere. The slowest sunsets and sunrises, on the contrary, happen around the time of the solstice. The reason is that at the equinox, the Sun rises due east and sets due west, so it’s the shortest path for it to sink below the horizon.
We hope you’ve learned something new about equinoxes from our article. If you have questions, please feel free to ask them on our social media. If you want to test your astronomical knowledge, take our quiz about equinoxes and solstices!
Text Credit: Vito Technology, Inc.