The 'Equinox Effect' Makes This Cosmic Phenomenon Even More Stunning, But Only Twice A Year

The northern and southern lights, otherwise known as the aurora borealis and aurora australis respectively, are some of nature's most awe-inspiring sights (alongside the ultra rare red rainbow phenomenon, which most of us will never experience). There are actually six different types of northern/southern lights, ranging from arcs and bands to pillars and even dunes of light, which were only observed as recently as 2018. Of course, you have to be in the right place to see the northern lights, but for anyone trying to catch this incredible natural display, it also helps to watch the sky at the right time of year — and the spring and fall equinox are prime viewing time.

In fact, the two equinox periods have a profound effect on the aurora borealis and aurora australis, with Earth aligning its axis in such a way that charged particles from the sun more easily enter our atmosphere, resulting in more frequent light shows. That makes the spring and fall equinoxes the perfect time to cast your gaze skyward and try to catch one of nature's most impressive visual displays. Luckily, Sept. 22, 2025 marked the point at which the sun crossed the celestial equator — the imaginary projection of our planet's equator into space — heralding the fall equinox and the first day of autumn. Aside from making days shorter and nights longer, it means that we'll see a spike in geomagnetic activity known as the "equinox effect."

The auroras we see in the sky above our planet actually begin with the sun, which emits streams of electromagnetic particles into space. Solar flares, or explosions on the sun's surface, alongside ejected gas bubbles, send these particles hurtling outward via what's known as solar wind. When they hit Earth's atmosphere, these particles collide with oxygen and nitrogen particles, transferring energy into the particles and causing them to glow various colors as the energy is released. These colors are most easily seen closer to the planet's poles, as the particles track magnetic field lines down towards the north and south poles. Depending on which gases are heated during this process, the resulting lights vary in color, with oxygen typically glowing green and nitrogen glowing purple, blue, and pink. Essentially, when we see auroras, we're seeing particles from the sun slamming into particles in our atmosphere, heating up, and producing a stunning light show.

During the two equinoxes, however, the resulting lights can be even more intense — though it also depends on whether the required solar activity actually takes place. The reason for this is that during an equinox, Earth's tilt means the planet is side-on with the sun, unlike during a solstice where it is either tilted towards or away from our star. During this time, the magnetic field of the solar wind carrying the charged particles from the sun is more attracted to Earth's magnetic field, which means more of the particles make their way into our atmosphere, resulting in more intense auroras when compared to the winter and summer months. This is known as the Russell-McPherron effect. While the likelihood of seeing an aurora increases during the two equinoxes, the solar activity that causes these light shows is still required. Luckily for those interested in catching the northern or southern lights, we're currently in a phase of solar maximum.

Our sun goes through an 11-year solar cycle, during which sunspots and solar flares increase and decrease. When this solar activity is at its highest, the sun is said to be at solar maximum. That means more particles will be emitted from our star as the activity on its surface sends energy out into space. NASA declared the sun to be at solar maximum in October 2024, but the term itself is also used to describe the two or three years around the peak month itself, during which solar activity is at its highest. That means we're still in a period of high solar activity, as shown by the National Oceanic and Atmospheric Administration's Solar Cycle Progression graphs.

What's more, early in 2025, scientists claimed that the sun could soon enter an even more dangerous phase than solar maximum, warning of a "battle zone" period during which two Hale cycle bands compete against each other. Hale cycles refer to how magnetic bands move across the surface of the sun, and the resulting "battle zone" could mean we see increased geomagnetic activity after the sun's solar maximum comes to an end. Meanwhile, a 2025 study published in IOP Science shows that, since 2008, the sun has reversed what had been a weakening trend and has seen a steady increase in solar wind activity, prompting NASA to warn that the coming decades could bring even more extreme space weather.

While that means spacecraft, astronauts, radio communications, GPS, and even Earth's own power grids could be more at risk, it also increases the likeliness of more intense auroras as the increased solar activity propels more particles toward our atmosphere. When you combine that with the equinoxes, you have the perfect recipe for more frequent and impressive light shows in our skies.