Abstract

Total solar eclipses are the grandest of personal astronomical phenomena. With decades of solar outreach experience, it was inevitable that my planning for the April 8, 2024, eclipse started years before. Involvement with NASA, NASA’s PUNCH Mission, and the Astronomical Society of the Pacific throughout the Heliophysics Big Year made this total solar eclipse the highlight of a lifetime of astronomy outreach.

1. The Eclipse Experience

In December 2022, I made specific plans for the total solar eclipse on April 8, 2024. A friend and I had viewed the 2017 eclipse together. Based on our 2017 experience, our site selection criteria for 2024 included the best weather prospects and not leaving the US. According to Jay Anderson’s eclipsophile.com site, Eagle Pass (Figure 1, right on the border-defining Rio Grande) had the best clear sky chances. So we acted accordingly. I rented an apartment, she a RV space.

2023 was a busy outreach year for me. I already had solar filters for my scopes. I made pinhole viewers from things like milk caps and colanders. Through donations, I purchased an H-alpha scope. All were put to work as I shared white- and red-light views of the Sun at dozens of events with thousands of folks at venues including the Grand Canyon, neighborhood parks, and libraries. The annular solar eclipse was a perfect ring from the center line at Chaco Culture National Historical Park. Along the way, I collaborated with members of several astronomical societies, NASA and ASP volunteers, outreach teams from the PUNCH mission, and former colleagues in the National Park Service.

2024 continued in the same vein, keeping me busy with solar sharing. I got hundreds of safe solar shades and distributed them far and wide. I invited five friends to share my Texas apartment with me. The rendezvous began as I drove 700 miles from my Albuquerque home through beautiful floral outbursts of bluebonnets, paintbrush, and yellow wildflowers across the Texas Hill Country. I reached Eagle Pass first. Two birders who had been camping for weeks at Big Bend joined me on Saturday, and three more biologists from Oregon and Washington joined me on Sunday. Our assembled naturalist geekfest got really stoked for Monday’s big event.

Meanwhile, the forecasts of the past week came true and the truth wasn’t good. Winds kicked up, and low clouds moved in. On Sunday, I met with a NASA team from Marshall Space Flight Center (MSFC) while at Garner State Park north of Uvalde. They were involved in public outreach and a number of experiments in the region, including in the towns of Del Rio and Eagle Pass. We set up scopes at the park for campers to look at the Sun. Mitzi Adams and Pete Robertson from MSFC were also coming to Eagle Pass on eclipse day.

On waking, low stratus clouds greeted us on Monday the 8^th. It looked like rain was brewing. It was all rather discouraging. My friends and I gathered our gear and traveled to the athletic complex that the city of Eagle Pass had reserved for eclipse watchers. Security there was tight, and my telescopes and cameras were inspected as if I were at an airport checkpoint.

I’d planned six projects during the eclipse. First off, unaided eye views of the eclipse, using filters as appropriate. Second was to share the eclipse through my C90 telescope, especially the unfiltered view during totality. Third, I planned to create a video of the entire eclipse with a small robotic telescope. Fourth, I planned to hunt for Comet Pons-Brooks with an 8x42 monocular at mid-eclipse. Fifth, I wanted to capture shadow bands with the same camera setup I’d used during the 2017 eclipse. Finally, I would attempt to capture the polarization of the corona with off-the-shelf camera gear. Yes, I rehearsed with all the gear and broke down when various efforts had to happen in the 4 minutes and 24 seconds of totality.

Hundreds of people gathered inside the sports complex. Many came over to look through the telescope at white-light views of the partial phases (Figure 2). The Sun was only occasionally visible through clouds. Every time it peeked through, a roar went up from the crowd. Shades on, look up! It was the biggest gathering I’d ever been at for an astronomical event, perhaps 1500.

Soon, it became evident that a triage would have to be made of my ambitious plans. I couldn’t get the roboscope to align and track the Sun, so simply left it for the remainder of the event. Mitzi had placed a sheet on the ground for the shadow bands, but it was too cloudy to even turn on that camera. As the morning and early afternoon wore on, most of us were in despair. Would we even see totality, much less a comet and other phenomena?

The day before, Pete had talked at Garner about the weather in Texas. Though clouds blanketed what had been predicted to be the best skies in the US for the eclipse, the cooling brought on by the eclipse had a possibility of chasing the clouds away around the time of totality.

Mid-eclipse was around 1:20 pm Central Time. Just after 1, sporadic glimpses of the partial phases seemed to become more frequent. The west darkened, although no definite shadow edge was seen. Was Pete’s forecast going to work for us?

And so it came to pass at Eagle Pass, just minutes before totality, that the skies cleared in a patch around the Sun that was about 30 degrees across! What a release of tension as the diamond ring glowed, went out, and the ghostly ring of the corona came into view.

I removed the filter from the scope and invited people to come over and take a look. Fantastic details in the corona and prominences were visible at high-resolution thanks to the unequaled dynamic range of the human eye.

“My god, it’s a naked-eye prominence!” These words from a seasoned NASA solar physicist conveyed the excitement of the moment.

Indeed, several large prominences made their appearance. One big one at the beginning of totality. Then, several more were uncovered towards the end. A gigantic pink-red formation was easy to see 3 minutes in, dubbed the Arch for its shape in the telescope.

Venus was bright to the west of the eclipse. Clouds cloaked Jupiter, and the part of the sky with Pons-Brooks, and I abandoned the comet search.

I couldn’t hear my personal timer over the crowd noise; fortunately, a big auditorium screen also gave the countdown.

As the clock closed in on 5 seconds remaining, filters were replaced, and lenses pointed away from the Sun. A cheer and applause went up from the audience in the stadium as a final diamond ring sparkled. Afterwards, the mayor gave a speech and group photos were snapped. Scopes were packed up, and farewell hugs were given to dispersing friends. An unforgettable astronomical phenomenon that had embraced us all ended all too quickly.

2. The Polarization Project

As I tended the scope and shared views through it, I had a chance to run my last project: capturing the polarization of the corona. I’d gotten the idea to do this demonstration from working with the NASA PUNCH mission folks during the 2023 annular solar eclipse. I used a DSLR camera, a stock 200mm telephoto lens, and a stock circular polarizer. Clouds challenged me here as well, as the lens had to be pointed and focused before totality.

The corona is the hot, ionized outer atmosphere of the Sun. Free electrons reflect the Sun’s light as a silver halo. The interaction between the photons and electrons polarizes the light, an example of Thomson scattering. Since the electrons are hot and fast-moving, any spectral features in the sunlight are Doppler-smeared out. This is the gray ghost ring highly sought after by eclipse chasers. Streamers and solar magnetic fields add their own effects, including the variation seen between activity maxima and minima over the 11-year solar cycle.

A photographer’s circularly polarizing filter is the combination of a linear polarizer followed by a circular quarter-wave plate polarizer so as not to interfere with beam splitters in various DSLRs and movie cameras (used for autofocus and metering). It polarizes with the quarter-wave plate (threaded side) closer to the camera and does not polarize the other way. (By way of comparison, polarized sunglasses are linear polarizers, with the maximum effect in a horizontal plane for glare reduction off of horizontally reflecting surfaces.)

A solar filter to aim and allow the focusing of the lens was fabricated out of blue gaffer tape, cardboard, foam, and half of a pair of safe solar shades. The setup was on a non-tracking tripod (Figure 3). I’d calculated bracketing exposures across a large range and programmed them in the camera days before. Just after the start of totality, I removed the filter, centered the Sun in the amply wide field of view, and triggered the shutter burst. I repeated this 3 more times during totality (during moments when I wasn’t busy at the scope or just gazing at the eclipse), rotating the polarizer each time. I didn't record angles during the eclipse, simply rotating the front (linear) filter element for significant visual effect between bursts (there were four bursts at four different angles). I got 84 exposures.

Right after the eclipse, just by flicking through the images in the camera, I could tell I’d been successful. Many images were useless because of remnant cloudiness. Later processing allowed me to find the best images and create a high-dynamic range movie clip that I could use when talking about the nature of the corona (Figure 4).

3. Conclusion

“Climate is what we expect. Weather is what we get.” Mark Twain’s quote couldn’t be truer for those traveling to Texas for the April 2024 total solar eclipse. As a NASA JPL Solar System Ambassador, I teamed up with scientists from the Marshall Space Flight Center. Despite the clouds defeating the fulfillment of several projects, I shared views of the uneclipsed Sun and partial phases with approximately 175 people over 2 days, and 10 lucky folks got a fantastic view of totality through my unfiltered telescope for over 4 minutes of totality. My personal success was documenting polarization of the corona’s ghostly ring.