Equinox 2025: What Is an Equinox?
The equinox is almost here — it will occur on March 20! In the Northern Hemisphere, this day signals the long-awaited end of winter, while in the Southern Hemisphere, it marks the arrival of autumn. But what exactly is an equinox, how is it connected with the seasons, and when will the next equinox occur? Keep reading to find out! If you want to know the exact time of the equinox for your location, check the Sky Tonight app.
Contents
- Equinox definition
- Equinox dates and times for the Northern Hemisphere
- Equinox dates and times for the Southern Hemisphere
- What happens during an equinox?
- F.A.Q.
- 5 interesting facts about the equinox
- Equinoxes 2025: Bottom line
Equinox definition
An 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.
Equinox dates and times for the Northern Hemisphere
When is the spring equinox in 2025?
The vernal equinox in the Northern Hemisphere will occur on March 20, 2025, at 09:01 GMT. This event marks the beginning of astronomical spring.
When is the fall equinox in 2025?
The autumnal equinox in the Northern Hemisphere will take place on September 22, 2025, at 18:19 GMT. This event signals the start of astronomical autumn.
Equinox dates and times for the Southern Hemisphere
When is the fall equinox in 2025?
The autumnal equinox in the Southern Hemisphere will occur on March 20, 2025, at 09:01 GMT. This marks the beginning of astronomical autumn.
When is the spring equinox in 2025?
The vernal equinox in the Southern Hemisphere will take place on September 22, 2025, at 18:19 GMT. This event signals the start of astronomical spring.
What happens during an equinox?
Day and night are almost equal
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. Check out our infographic to learn more reasons why day and night aren’t exactly equal on the equinox.
The Sun rises exactly in the east
Another interesting phenomenon that occurs at the 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.
Best time to see the auroras
The weeks around equinoxes are among the best times to observe the northern lights (aurora borealis) and southern lights (aurora australis). During March and September, the Earth's magnetic field interacts more efficiently with the solar wind, leading to increased geomagnetic activity. This results in stronger and more frequent auroras, especially near the Arctic and Antarctic regions. So if you want to see an aurora, plan your observations around the equinoxes!
Best time to see the zodiacal light
Equinoxes also offer prime conditions for observing the zodiacal light — a faint, cone-shaped glow that appears in the sky just after sunset or before sunrise. This light is caused by sunlight scattering off interplanetary dust particles in the Solar System.
In the Northern Hemisphere, the best time to see the zodiacal light is in the evening after sunset around the spring equinox. In the Southern Hemisphere, it is best seen before sunrise around the autumn equinox. During these times, the zodiacal light extends high above the horizon, making it easier to spot.
F.A.Q.
What is the difference between the equinox and solstice?
Both equinoxes and solstices mark the change of seasons, but beyond that, they are opposites:
- An equinox is the 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 2025.
Is the March equinox the first day of spring?
The March equinox marks the beginning of astronomical spring in the Northern Hemisphere and occurs between March 19 and 21, depending on the year and your time zone. In the Southern Hemisphere, spring begins with the September equinox, which falls between September 21 and 24.
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. In 2025, the closest Full Moon to the March equinox will occur on March 14. It is known as the Worm Moon in the Northern Hemisphere. The closest Full Moon to the September equinox will occur on October 7. It is traditionally called the Harvest Moon in the Northern Hemisphere.
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 main 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 summer solstice) and the fewest hours of daylight (the winter 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.
Equinoxes 2025: Bottom line
The next equinox in 2025 will occur on March 20 at 09:01 GMT, marking the start of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. During an equinox, day and night are nearly equal worldwide, and the Sun rises due east and sets due west for all locations except the poles. This astronomical event also brings enhanced aurora activity, making it one of the best times to see the northern and southern lights. Want to test your knowledge of the equinoxes? Take our quiz!
