Totality is fleeting. To stand in the shadow of the moon is both a huge privilege and a huge achievement, but the shadow of the moon does not hang about. As it zips across Earth at 1,500 mph (2,500 kph), it affords a view of the totally eclipsed sun—and its white, wispy corona—for just a few minutes. See the corona, our star as it really is, can only be a moment.
Continuous Corona
Unless that is, you have a total solar eclipse that surges across over 3,700 miles (6,000 kilometers) of a single country with a well-organized, well-resourced science community. On April 8, that’s exactly what will happen for the second time in under seven years. Cue the Citizen Continental-America Telescopic Eclipse (CATE 2024) project, an attempt to make a continuous 60-minute high-resolution movie of the sun’s corona using 35 teams of three or four citizen scientists, each using sophisticated but standardized cameras and setups.
America’s 68-Minute Totality
Although solar researchers have been taking images of the sun’s corona during totality for many years, it’s rare to have the chance to take so many photos in succession for so long. Totality will move across North America in 100 minutes, crossing six timezones, with anyone below in the path experiencing up to 4 minutes and 28 seconds of totality. In the U.S., totality will begin in Texas at 1:27 pm CDT and end in Maine at 3:35 pm EDT—a total of 68 minutes split between two timezones. CATE 2024 is only possible because much of the path is on land.
Collective Observations
“The idea is that you let totality pass over lots of groups so you can collectively observe it for a long period of time,” said Dr. Amir Caspi, principal scientist at Southwest Research Institute in Boulder, Colorado and in charge of the experiment, in an interview. “The tricky bit is that since you have multiple people, cameras and equipment, you have to find a way to join together all of that data in a way that makes sense.” To that end, exactly the same cameras, telescopes and training so they can make exactly the same kinds of observations. The equipment was successfully tested at the last total solar eclipse on April 20, 2023 in Western Australia.
Complex Corona
It’s hoped the movie will allow scientists to study the corona’s complexities. During totality, it’s possible to see various features on the surface of the sun with the naked eye, the most obvious being prominences—pinkish loops of plasma. However, since the “movie” will last about an hour, it may be possible for CATE 2024 to capture processes on the sun that take seconds or minutes—and so which are typically not seen during a brief totality—such as a solar flare or a coronal mass ejection, as well as waves and jets.
A solar flare is an eruption of electromagnetic radiation in the sun’s atmosphere. They’re caused by twisted magnetic fields, typically above sunspots—cooler, darker regions of the sun’s surface that form when clumps of its magnetic field well up from deep within the sun. They travel towards Earth at the speed of light. A coronal mass ejection—a large expulsion of plasma and magnetic field from the sun’s corona—can take a couple of days to reach Earth.
Flares and CMEs have been seen before at some eclipses, but rarely. With the sun now at solar maximum—the peak of its 11-year cycle of magnetic activity—2024’s totality could be a very special sight.
However, CATE 2024 will go much further than just increasing the odds of capturing something fleeting.
Polarized Light
CATE 2024 will also seek to polarize the light coming from the sun’s corona during totality. “The corona is permeated by a complicated magnetic field,” says Caspi. “During totality, we don’t see the magnetic field, but instead the hot plasma trapped along it – just like being able to see iron filings around a magnetic field around a magnet.” However, the light coming from the corona during totality has something in common—it’s almost entirely polarized.
“When you see the corona during totality, you’re actually seeing scattered light from the surface of the sun that hits all of the electrons in the corona, and then it scatters away—including towards you, which is what you see,” said Caspi. That directional aspect means one thing. “If you can measure the angle of polarization, then that gives you a 3D structure of the corona, its density, and how that changes over time,” said Caspi. This is the K corona, named Kontinuierlich (German for ‘Continuum’). “When we put all the data together, we will have polarized measurements for one hour, and we’ll be able to see the three-dimensional structure of the corona.”
For the very latest on the total solar eclipse—including travel and lodging options—check my main feed for new articles each day.
Wishing you clear skies and wide eyes.
