Aurora Borealis

 

Aurora on October 10, 2024

Last night was the second night in 2024 when an aurora reached as far south as Tucson, Arizona. At least, as far as I know. The first one, last May, caught me by surprise. I had seen some nice sunspot groups and I know that solar flares and coronal mass ejections (CMEs) can give beautiful auroral displays in the far north. A few days later, I got a notification on my phone from, of all places, the MyRadar app. It said, "Aurora visible now!" I was skeptical that we'd see anything this far south. But I went outside to look anyway. As I expected, I didn't see anything unusual in the evening sky. Then my daughter used her iPhone to take a picture and there it was! Spectacular red color and vertical bands! Astonishing! 

Tonight's aurora was a wee bit more visible to the unaided eye than that one. But it was still much better and plainly obvious in pictures. And MyRadar hadn't said a word. My sister in Pennsylvania alerted me to the aurora and sent some of her pictures. That made me curious, even though from what I saw in the news reports, the aurora was predicted to be visible only as far south as maybe Kansas. I went outside to take a look and, sure enough, the sky to the north looked a little redder than elsewhere. My old-model iPhone doesn't have a good enough camera, so I took some pictures with my DSLR that revealed the reddish glow and vertical bands much better than my eyes could see. Awesome!

It was my mother, God rest her soul, many decades ago who first introduced me to the Aurora Borealis, or "Northern Lights." Well, she was the first one I can recall using those words. She pointed to something in the sky while we were riding in the car at night, and she said, "Oh, look! The Northern Lights!" I looked and looked but couldn't see anything out of the ordinary. It was the same sort of thing that had happened before while riding in the car at night. She said, "There's the Big Dipper." I looked and looked but could not see a "dipper." I didn't realize that she was referring to a group of stars. In truth, I had no idea what she intended for me to see. She didn't explain it further, and I didn't ask about it because I wanted her to think that I knew what she was talking about.

To be fair, my mother was not an amateur astronomer. Nor was she a dedicated skywatcher. On that one particular nighttime car ride, she may or may not have witnessed an aurora. Perhaps she merely saw the glow of city lights on the distant horizon and mistook it for the "Northern Lights." I'll never know. But if my most recent experiences with aurorae are typical, it's doubtful that my mother could have seen the subtle glow of an aurora while riding in the car.

There was a time not too long ago when the news media didn't make a fuss over a possible aurora. Solar weather forecasting may not have been as well developed as it is now, but even when solar researchers had made vague predictions about a possible aurora, it was considered "science news" and it wouldn't have been picked up by the popular news outlets. Why bother to tell the masses about an aurora? Who's going to go outside at night to shiver in the cold and look for something they don't understand? Besides, with all the nighttime light pollution in cities and towns, they probably wouldn't be able to see it anyway. If we ever witnessed an aurora in those years, it would have been through our own discovery, by casually observing the nighttime sky. Like while riding in the car with our parents. Why should riding in a car be significant? Because when I was a kid, I didn't spend much time outside after dark. If I did for some reason, there were lots of bright yard lights that ruined my night vision, so I wouldn't have seen the stars very well. But riding in a car at night was a different story. We were often riding in the country at night, with no lights but the car's headlights, and my siblings and I would look up into the sky at the stars through the side windows, saying nothing to one another.

It's not surprising then that prior to 2024, with no alerts from the news media, the last aurora I witnessed was back in 1989. As a telescope operator for an observatory in the mountains of New Mexico, we were taking sky flats after sundown, and while shooting with the red filter, we were horrified at the sight of a bizarre pattern of concentric rings in the images. What the—? Did our camera just break? One of the astronomers present instantly recognized it as optical fringing, something that occurs, according to him, when viewing monochromatic light through a narrowband filter of similar color. In this case, he said, there must be an aurora. We're looking at the red light of an aurora through the red filter. We went outside to have a look at the sky and it was, indeed, very red! Brilliantly red, as if it were on fire!

Excited about seeing my first real aurora, I grabbed my SLR film camera and tripod and took a picture (see below). There must have been quite the solar flare to produce an aurora that was visible as far south as Albuquerque, NM. Later, we learned that some people in the city were alarmed by the color of the sky and had called the authorities to find out what was going on. Nobody knew that it was an aurora.

Aurora in New Mexico, March 1989

There are two interesting things that stick in my mind about that night in March of 1989. First, how in the world did the astronomer put those three things together so quickly (optical fringing, red filter, red aurora)? And secondly, how did we see the aurora so easily with our unaided eyes? Did the astronomer have some insider information about recent solar activity, so that he was secretly expecting something like that to happen and could thus impress us with his vast knowledge of optics? And as for the bright and obvious pink color of the sky, I can say only that had we gone outside that night and saw something subtle like these two recent auroral displays, I wouldn't have bothered to take a picture, and I more than likely would have doubted whether the optical fringing in our CCD camera was due to an aurora. As it was, the first thing we saw was optical fringing. Then the astronomer gave his theory. And when we went outside, we immediately saw the proof of his theory with our very own eyes!  

I must admit that all of this is still somewhat mysterious to me, even as I write this. I have now witnessed three separate events of "far-south aurorae." One of them was obvious to the unaided eye. The other two were not. Why? Was it the high elevation at the observatory (over 9,000 feet) that made the aurora of 1989 easier to see? Or was it perhaps the fact that there was no light pollution in the mountains? Another puzzler is that two of them produced optical fringing: the one in 1989, with the observatory's camera, and the one last May, with my DSLR (see below). That pattern of concentric rings was in all of my pictures of the aurora of May 10, 2024. At the time, I suspected it was similar to the fringing in 1989, perhaps having to do with the IR cutoff filter of DSLRs. But last night's aurora gave no such fringing pattern in my pictures from the same camera. Was the color in last night's aurora a slightly different shade of red than the one in May? Hmmmm.

Fringing from the aurora of May 10, 2024.