On the night spanning both Friday and Saturday, May 10-11, 2024 there was an unusually powerful geomagnetic storm. It resulted in ionic glowing of the upper atmosphere all the way south across the USA to latitudes as low as south Texas and central Florida. This included pretty much all of Arizona. As a result of this unexpected visitation of the aurora borealis all the way into the subtropics, I was able for the first time to catch images of the glowing pink sky via time exposure alongside my desert garden.

A geomagnetic storm is the result of coronal mass ejections (CME) that emanate into space from the surface of the sun, especially ones that happen during periods of elevated solar activity every 22 years or so. (The alternate cycle of low activity occurs every 22 years also but in an opposite phase, meaning that every 11 years we have a peak or a valley as the case may be.) CMEs involve eruptions of plasma from the sun’s corona that are flung into space and escape the gravity of the sun, heading outwards into the solar system. A large CME will involve around a billion tons of highly energized and magnetized particles. They usually take around two days to cross the space distance between the sun’s heliosphere and the Earth, but speeds do vary between one and several days depending upon the size and strength of the CME.

Most CME events are not strong enough to cause the ionization of gases in the atmosphere very far from the Earth’s polar regions, where auroras are relatively commonly seen, comparatively speaking. According to various online sources, the aurora borealis occurs almost every night of the year in both polar regions, but that does not mean that they are always visible or easy to observe.

Of course both the weather and the time of the day/year play overriding roles in whether an auroral event can be seen, as does geographical location and the actual strength of the CME impacting the planet at those times. Obviously the aurora borealis is not visible during the daytime, which means that in summer there is less opportunity to see it than in the winter due to fewer hours of darkness up north. Clouds easily obscure most auroral events, and going farther south also tends to quickly diminish the observed brightness of the show. And as referenced above, not every CME is very potent and many (especially during 11-year solar minimums) are quite weak and dim. Additionally, not every CME actually intersects with the Earth’s orbit at peak intensity, and the less solar wind there is, the fewer particles there are to interact with the Earth’s magnetic field and atmosphere, resulting in less showy auroras.

The May 10-11, 2024 geomagnetic storm was as strong as any hitting earth had been in the previous 20-plus years, since late October 2003. Social media sharing platforms essentially did not exist back then, and online news coverage was still in its relative infancy. While there was definitely some information floating around at the time, most people simply missed the 2003 auroras that went fairly far south simply because they didn’t know it was happening. Auroras are already very ephemeral and often fast-moving events, even up north, and they can easily be missed.

The May 2024 aurora was widely seen in both the northern and southern hemispheres compared to prior ones. Improvements in geomagnetic storm “space weather” forecasting had set the stage of positive expectation in advance, and then when it actually started happening the widespread use of social media and telecommunications accessible to almost everyone made sure that many people didn’t miss out on this cycle. Naturally not everyone is connected at all times, and the fact that auroras are only visible at night meant that many people were in fact sleeping during the peak overnight hours. Plus the aurora is not visible everywhere equally, nor at all times even in the fortunate places. And urban light pollution can easily dim down the auroral viewing, not to mention cloudy weather. At least the crescent moon set not long after sunset, so that left a dark sky with improved visibility in many places provided there were few or no clouds.

There is much more habitable landmass in the northern hemisphere than in the southern, so the aurora borealis is much more widely seen than the aurora australis, which occurs mainly over the southern ocean and icy Antarctica where there are exceedingly few human observers or their technological instruments. Whenever there is a large CME and a strong geomagnetic storm, the aurora australis will be just as powerful as the northern lights are – but it will simply be far less observed.

The colors of the aurora vary both with the type of gas being ionized and the elevation of the gas within the Earth’s atmosphere. The most common auroral color is a yellowish-green, caused by oxygen molecules lower in the atmosphere. This is the color most familiar to observers at high latitudes both northerly and southerly. Oxygen molecules at high elevations closer to the outer edge of the atmosphere are often ionized to emit red wavelengths, which is actually fairly rarely observed in polar regions, and is ironically more usual for strong geomagnetic storms farther south. This is partly because red oxygen wavelengths are more easily created in the upper atmosphere at lower latitudes, while yellowish-green oxygen wavelengths are not since the solar storm isn’t as strong farther south. In the north the higher energy of the storm operating closer to the magnetic poles allows for deeper penetration lower into the atmosphere, thus resulting in green light from oxygen there. Red light from upper-level oxygen is also formed but is often overwhelmed by the much brighter yellow-green colors beneath them and closer to the viewer’s eyes.

Nitrogen gas is the most abundant element in our air, and when ionized it emits mostly blue wavelengths of light. Depending upon the density (depth) of the atmosphere, nitrogen can also emit red wavelengths, which when mixed with the predominant blue yields purple. Different energetic excitement levels dictate the wavelength of light emitted in both the dominant oxygen and nitrogen gases, and the color-blending effect can yield colors that aren’t necessarily being emitted by one gas alone. While there are also other gases in the air, the proportions are so small that it is mostly O2 and N2 that dictate the colors of the aurora, again dependent upon the level of energizing and the atmospheric density.

Earlier in the late afternoon and evening on Friday May 10, 2024 I had taken a hike in the Hualapai Mountains foothills with my herpetologist friend Michael from Tucson in search of rosy boa snakes (Lichanura trivirgata) and any other reptiles that we might have uncovered. While we didn’t find any rosy boas, we did catch and photograph a feisty lyre snake (Trimorphodon biscutatus) and a desert spiny lizard (Sceloporus magister). We parted ways by about 10 PM and I went home, not noticing anything in particular in the sky as I drove back.

Getting onto my phone inside the house, I started seeing social media posts of the ongoing aurora in places that normally never see it. My friend Cody in Idaho messaged me photos that he had just taken from outside of Twin Falls of a red and purple sky, taken with his cell phone. I went outside and looked at the sky and saw that it was unusually red, although to be honest it was quite subtle and easily missed were you not deliberately paying attention.

The first photo I took was one using the “night sight” setting on my phone camera. The results that were returned after a several-second handheld exposure were on the blurry side (it was past 11 PM and fully dark, with the crescent moon having set) and luridly red. Not a very good photo. But what it did do was to illustrate that the aurora was really happening and that cameras were picking up on things that the human eye couldn’t fully see. As such I immediately hauled out my much superior-for-the-purpose DSLR camera and a tripod, so that I could craft the images I’ve been featuring above with my home and desert garden flora.

Cameras do not “see” light in the same way that human eyes do. Humans and other animals see light and resolve physical images in their brains from instant to instant in a continuous live feed that is restricted to whatever is environmentally present at a given moment. If it is dark outside, animals can only see what exists via the low intensity of light that is present. Of course animals have a wide variety of ways of amplifying their visual acuity by both day and night, via adaptations such as extra cells in their retinas to create sharper vision or greater sensitivity to low light conditions; faster brain processing speeds for creatures that fly and must respond quickly to new stimuli, threats, and opportunities; and evolving to become more attuned to other electromagnetic frequencies such as seeing in the ultraviolet or infrared portions of the spectrum.

One thing that animals, to my knowledge, do NOT do is see light in a cumulative fashion. Cameras and other types of electronic equipment have been engineered to be able to do this. These devices can gather low light levels over time and then process it into a single image that can reveal details that are not visible to animals under low light circumstances. We’ve all seen time lapse photos that show the earth’s rotation in the form of stars wheeling overhead, or videos that show the motion of clouds, storms, tides, traffic flow, and the like happening at compressed speeds that simply do not occur in physical reality. Space telescopes do the same things, frequently gathering extremely low and distant light sources and combining them into composite images that hint at how distant cosmic objects might appear to the human eye, were we able to somehow teleport ourselves to be much closer to them. This ability to “stack” light cumulatively over time and through space is how technology allows us to see in ways that our eyes and brains cannot.

Digital cameras and phones are able to pick up the red wavelengths and amplify them via time exposure to a level that is more visible to us, and then easily display it on a screen. Longer exposures and higher sensitivity settings enabled cameras of all types to capture a wide range of colors in the global skies. When paired with the endless variety of foreground elements and landscape settings people were in, it made for a uniquely memorable and positive shared human social, cultural, and scientific experience.

Not only was it easy for the average person to take decent quality night photos using technological devices that nearly everyone nowadays owns, but we could then share the photos with dozens to potentially millions of others in ways that were largely unthinkable to most of us 20 years ago. The Halloween 2003 geomagnetic storm was an event of similar scope and intensity as this one in 2024 was, and was also the last time the aurora made it so far south. Due to both technological and social changes, the May 2024 aurora was the best documented and most widely viewed solar storm in history. It’s not hard to imagine that the next one will be even more so.

To close, I’ll add this image from Sunday May 12, 2024 taken at about 9:30 PM from just outside my front door. It’s a thoroughly average and more or less expected night image of 30 seconds long at 500 ISO, the same basic parameters that all the red sky photos I took above also had. No aurora borealis is anywhere to be seen, and aside from a bit of a light pollution dome from Las Vegas 150 miles to my northwest, there’s nothing abnormal about this particular night sky’s coloration. It’s dark, and there are two faint light streaks caused by passing aircraft near the saguaro to the right. It’s an acceptable image but certainly nothing to get excited about. The ionized glowing red oxygen light of two nights before was decidedly more spectacular.

Space weather experts had suggested that there might have been a repeat of another CME hitting Earth overnight on the 12th and 13th of May, 2024 – but despite repeated attempts at random times over the course of 5 or 6 hours to catch it again, there was nothing. To be fair, space weather is extremely challenging to predict. It originates a great deal farther away and is also much rarer, with much less data to help analyze it, so there’s no one to criticize here. Instead I think it underscores how amazing it was to see an Arizona Aurora. I hold out hope that it might yet happen again some day.