'Like the twilight zone' – The life-changing experience of a total solar eclipse
This black-and-white image shows the 2017 total solar eclipse, revealing the corona flaring out from the sun as it is eclipsed by the moon. (Photo by Vishnu Reddy/Department of Planetary Sciences)
Vishnu Reddy, professor, Department of Planetary Sciences and the Lunar and Planetary Laboratory
Nick Letson, marketing and communications manager, Flandrau Science Center and Planetarium
On April 8, a 100-mile-wide shadow will race toward the Pacific coast of Mexico, just below the tip of Baja California, at the speed of sound. For those living on the North American continent, this will mark the beginning of a highly anticipated celestial spectacle: the total solar eclipse of 2024.
While solar eclipses happen two to three times each year, not all of them are total, and few occur in areas with densely populated swaths of land, which makes the upcoming eclipse particularly special. For those in North America, the next total solar eclipse won't happen for another 20 years.
The path of the "Great American Eclipse," as it is widely referred to, leads across Mexico's Sierra Madre mountain range into southwest Texas, skirting Dallas, then heading northeast toward St. Louis and Detroit before traversing Canada just south of Toronto and Montreal and finally moving across Newfoundland and the Atlantic Ocean.
Vishnu Reddy, a professor in the Lunar and Planetary Laboratory and Department of Planetary Sciences, is gearing up to travel to Fredericksburg, Texas, a location he chose because it is smack dab in the middle of the path of totality.
"To get the full experience, you absolutely have to be inside the path of totality," Reddy says. "Often, I hear people say, 'Oh, where I live, it’s 99% of totality, so I don’t need to travel 100 miles to see 100%.' But that's a misconception. The difference between a 99.8% partial eclipse and 100% totality is like night and day."
This is because the sun shines so brightly that it will overpower anything unless the moon obscures it completely.
Solar eclipses happen when the moon moves into the line of sight between the Earth and the sun. A crucial ingredient in the magic that makes for a total solar eclipse is a whim of nature: The relative size of the moon's disc exactly matches that of the sun when viewed from Earth. If it wasn't for this cosmic coincidence, solar eclipses would not nearly be as awe-inspiring as they are when viewed in the path of totality.
The reason each new moon does not result in a solar eclipse is because the moon's orbit around the Earth is tilted with respect to the Earth's orbit around the sun, Reddy explained.
"That's why solar eclipses are big deal," he said. "They're rare, because most of the time during a new moon, the sun won't fully hide behind the moon."
Reddy says that even with today's technology, there still is something special about witnessing a total solar eclipse that can't be accomplished otherwise. Typically, researchers who study the sun have to suppress its intense brightness using a device known as a coronagraph if they want to detect our star's more tenuous features, such as the sun's corona, which can be thought of as the outermost wisps of the sun's atmosphere, which is called the chromosphere.
The corona makes for the most spectacular feature during a total eclipse, and it's the only time it is visible to the naked eye, Reddy explained.
"The chromosphere is a different layer about 250 to 1,250 miles above the photosphere. It's extremely difficult to photograph because it's hidden in the bright sunlight," Reddy said. "The only time it appears is during a total solar eclipse. During those 4 minutes and 28 seconds, nature provides us with a coronagraph that allows us to see features that aren't normally visible."
Those planning to travel into the path of totality will need proper eye protection from the time the eclipse begins until it reaches the stage referred to as the "diamond effect." This visually stunning phenomenon occurs in the last few seconds before the moon's disc covers the entire sun. At that time, the sunlight shines through crater valleys and troughs of the lunar horizon, resulting in what looks like a brilliant ring studded with diamonds. The same effect will appear just after totality, as the moon's disc slips across the sun, this time lighting up "diamonds" on the opposite side
"Many of us don't really think much about the sun on any given day beyond trying to not get sunburnt," Reddy said. "A solar eclipse is a way to get millions of people interested in our very own star. It is our way to get people to focus on science, and it's also the first total eclipse since the COVID pandemic."
The sun – an everyday sight, yet still mysterious
There are things about the sun that scientists specializing in heliophysics still don't understand. For example: Why the sun's corona, which consists of highly ionized gas also known as plasma, is much hotter than its surface.
Spacecraft such as the Solar and Heliospheric Observatory, a joint mission between NASA and the European Space Agency, observe the sun with spectacular detail. A t the same time, there is a huge potential for using the eclipse to collect new datasets, Reddy says.
"For example, if you have an instrument that's too large to go on a spacecraft, or if you want to try out new technology that isn't mature yet to be put on a spacecraft, you can use ground observations to study the sun in a new way, and solar eclipses offer great opportunities to do that," he says.
See the eclipse on campus
Flandrau Science Center and Planetarium will hold a special event on the day of the eclipse, offering:
- Solar telescopes on the Mall.
- Reduced admission prices for visitors interested in seeing Flandrau's science exhibits.
- Viewing goggles for purchase ($2).
- A livestream showing views of the total solar eclipse.
- A new fulldome show called "Totality!" in the planetarium.
"It's the next best way to see the event for those of us who can't go to the path of totality," said Nick Letson, Flandrau's marketing and communications manager. "We invite the community to experience the solar eclipse right here, where they can get excited about the event and learn about the mechanics behind it at the same time."
"Seeing a total solar eclipse is life-changing," said Reddy, who traveled to Wyoming to experience his first – and so far only – total solar eclipse in 2017. "There really is no other way to put it. The atmosphere – all the people watching with you, the light, the color of the sky, the crispness of everything – it's surreal. It’s like you are in the twilight zone, you know?"
Get eclipse-ready
Those willing to stay up late will be treated to another celestial event: a penumbral lunar eclipse, which is when the full moon dips into the Earth's shadow. Visible from Southern Arizona, the eclipse will peak around 1:12 a.m. Tucson time on March 25.
On April 6, Flandrau will hold "Science at Sunset: Eclipses and the Ring of Fire," which includes the debut of the "Totality!" fulldome show and a presentation by Nicole Kerrison, a graduate student at the Lunar and Planetary Laboratory.