One reason was that photographic plates weren’t large enough to capture the full 17-inch-wide image. But observations by eye and hand have other advantages over those early photographs, notes Padilla, especially when the seeing is poor and turbulent air in the atmosphere distorts the image. “Your eye will integrate the detail,” says Padilla. “Even if the seeing is not perfect, if you get moments of sharp seeing, your eye will note that and you can draw in that fine detail. Whereas with a photograph, if you had a moment of bad seeing, you’d come up with a blurry image and not much detail.”
Lee, Moon, and their colleague Eunsu Park took a set of Mount Wilson sketches drawn by Padilla and other observers from 2011 to 2015 and fed them into the algorithm, along with the actual corresponding UV images from SDO. They also provided the model with same-day SDO magnetograms, which are maps of the Sun’s magnetic field strength that indicate the polarity of the field at active regions.
The model, published Feb. 5 in The Astrophysical Journal, generates artificial images that are strikingly similar to the real UV images. And in the generated magnetograms, the team found the model is able to reproduce a characteristic signature of active sunspot regions — side-by-side patches of opposite polarity — even though the model has no knowledge of the physics involved.
Next, they turned their model loose on Galileo’s sketches. Since he made several weeks’ worth of drawings tracking changes in the Sun’s surface, the team was able to use the model to calculate how magnetically active these regions were at the time, how they evolved, and how they would look to modern satellites.
Giving Galileo’s sketches a facelift isn’t the only thing the new model can do. Lee and Moon hope that it can also help them analyze other historically significant solar storms captured in sunspot sketches — like the famous Carrington event of 1859, which created aurorae seen in locales as close to the equator as Cuba. Understanding these massive solar storms has never been more important: Today, they threaten electrical grids, satellites, and even the safety of astronauts.
Long-term payoff
Ulrich hopes this work is the start of something he had long hoped for. “The idea of going back and kind of resurrecting old global magnetogram structures for the Sun has always intrigued me as something that would be valuable,” he says. “The sunspot drawings have some of that information, but obviously not enough of it without this other AI approach.”
One limitation of the model, however, is that it doesn’t reproduce non-active regions of the Sun with weak magnetic fields, which Ulrich says would be necessary to get a comprehensive picture of the Sun’s magnetic field at any given moment, past or present. Though he admits it might not be possible to solve, he says “it certainly would be worth checking out.”
Ulrich and his team were forced to cease research at the 150-foot solar tower in 2012 due to equipment failures and a lack of funding. But he’s gratified to see that their efforts to digitize the records have been useful. “That’s part of why I wanted to get the drawings out there to people,” he says.
In the meantime, Padilla plans to keep living at Mount Wilson and continue his sketches — for as long as he can. The observatory survived a close call with conflagration in the 2019 Bobcat Fire. With the facility nearly consumed by flames, Padilla was forced to evacuate. “I could see the huge plume of smoke every day,” he says. “In the evening, you could look up and see the red glow of flames burning.”
Then, a few months after he returned, the observatory was shuttered by the COVID-19 pandemic. With the mountaintop bathed in an eerie quiet, Padilla watched bears and other wildlife return. “It was going back to a more natural state,” he says.
All the while, he continued his daily routine of opening up the solar telescope and sketching the Sun. “That was a good thing for me in the midst of the pandemic,” says Padilla. “It gave me something to persevere with.”