When a total solar eclipse passes over Rochester, New York, on April 8, three first-year students will help NASA study the sun’s corona. Asad Shahab ’27, an major, along with majors Adam Bowen ’27 and Michael Koomson ’27 formed one of more than 30 teams nationwide—from Maine to Texas—participating in the .

The experiment, coordinated by the Southwest Research Institute in partnership with NASA, aims to understand how the sun’s corona varies across the . It will compare analyses between 2017, shortly before solar minimum, and 2024, near solar maximum. Stitching together recordings from more than 30 points along the eclipse’s path will provide scientists more than an hour of observations of the sun’s corona, which is normally difficult to study because it is millions of times dimmer than the sun’s surface.

Shahab stumbled upon the project when he saw an online ad soliciting participants. He viewed it as a chance to continue the astrophotography hobby he developed as a child.

“I had a telescope back home in Pakistan and my mother got me active with it when I was eight or nine,” says Shahab. “Astrophotography has been a hobby of mine for a long time and when I saw the Google ad looking for participants, I thought, ‘I have to do this.’”

Shahab asked Bowen and Koomson, two of his friends from his dormitory floor, if they wanted to join him. The trio applied and was chosen to lead efforts for the region despite other competitive applications from the Rochester area.

NASA provided the team a telescope, mount, camera, laptop, and other equipment for taking their observations. The telescope will be outfitted with a solar filter and will track the sun throughout the entirety of the eclipse, taking images at regular intervals. When the moon is completely covering the sun, the students will remove the filter and record a video of the solar eclipse in totality.

Shahab says he’s excited to contribute to such meaningful research and is honored to represent Rochester as a member of the nationwide citizen science team.

“Who doesn’t want to participate in something sponsored by NASA? It’s a dream,” says Shahab.

In medieval and Renaissance society and culture, celestial events were not mere spectacles in the sky. Rather, they were omens, predictors of the future, and windows into the workings of the universe. Ģ����ý historian and librarian Anna Siebach-Larsen, director of the , shed light on how the people of the (falsely labeled) “Dark Ages” actually understood, interpreted, and experienced eclipses, planetary conjunctions, and other astronomical phenomena.

Eclipses were well understood in medieval Europe—at least mathematically.

Forget the idea of flat earthers and the notion that medieval people “were generally stupid, ignorant, and superstitious,” says Smoller, a professor of history at Rochester and a fellow of the Medieval Academy of America. Ancient and medieval astronomers “knew quite well how to predict when conjunctions and eclipses were going to happen,” she says.

They understood that if the moon was either new or full, and when its path crossed the ecliptic—the sun’s path—you had an eclipse (a solar eclipse with the new moon and a lunar eclipse with the full moon). During an eclipse, the sun and moon are either in opposition (180 degrees opposite each other) or in conjunction in the exact same degree. But their paths have to be on the exact same plane and need to have crossed, explains Smoller. “That’s mathematically pretty sophisticated to conceive,” she says.

That said, medieval Europe still held a strictly Earth-centric view that considered the sun and the moon to be planets that orbit Earth—along with the five then-known planets Venus, Mercury, Mars, Jupiter, and Saturn. This geocentric model was not just specific to the Middle Ages—indeed, it was the predominant model in several classical civilizations, including ancient Greece and Rome.

In 1543, the publication of De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) by Renaissance astronomer and mathematician Nicolaus Copernicus would kick off the Copernican Revolution. His work ultimately led to the long-held Earth-centric model’s being replaced with a heliocentric one that has the sun at the center of our solar system.

Celestial events like eclipses were used to predict the future, including the weather.

Medieval Europeans saw alignments of planets, like conjunctions of Jupiter and Saturn, as signs of things to come—from famines, earthquakes, and floods, to the birth of Christ, and even the collapse of empires. They believed that eclipses, especially solar eclipses, could amplify and strengthen the effects of these planetary conjunctions.

The University’s (RBSCP) is home to an early printed book from 1485 by Firmin de Beauval titled (On Predicting Changes in the Weather), published by Erhard Ratdolt, who specialized in printing works of geometry, astrology, and astronomy.

A compilation of ancient medieval sources, the treatise deals with the influence of planets on meteorological phenomena and weather forecasting. But it also covers solstices and equinoxes, planetary conjunctions, and eclipses—and their reported ability to prognosticate the future.

Reading the original imprint (or incunable) in Latin, Smoller notes that eclipses were considered to boost the effects of planetary conjunctions. According to the text, when a solar eclipse is combined with the planetary conjunction of Saturn and Jupiter in the head of Aries, “the effects will last 12,000 years.” That staggering number is not a typo. Smoller points to faded marks in the right margins that an early reader, likewise astonished at the described super-booster effect, made in the same passage.

Smoller pushes back against the conventional notion of the superstitious Middle Ages. “I don’t think it’s superstitious on their part to believe that things that happen in the heavens have an effect on Earth,” she says, pointing to the example of tidal changes that are synched with the moon cycle. “That is the nature of medieval, ancient, and a lot of early modern natural philosophy, including beliefs held by Galileo and Kepler.”

Medieval theologians pondered the meaning of the “miraculous eclipse” that apparently occurred during Jesus’s Crucifixion.

The study of eclipses was, unsurprisingly, essential for specialized astronomers. But it also formed part of a general university education during the Middle Ages, including for theologians.

Take the example of William of Auvergne, the bishop of Paris from 1228 to 1249 and a prominent theology professor at the University of Paris. William is one of many writers to discuss the purported “miraculous eclipse” that occurred at the time of Jesus’s Crucifixion. With the 600-folio De universo, which translates to On the Universe, William provides “an extraordinary look at the culture of scientific thought and the ways in which it was transmitted,” explained Siebach-Larsen . The manuscript boasts an unusual illumination that is broken into the four elements: earth (complete with mountains and trees), water (with fish), air (with flies), and fire. (Want to take a deeper dive into the De universo manuscript? Take a .)

An early witness to the idea of “natural magic” among medieval thinkers, William covers the topic of eclipses in De universo. He counts among the many Christian writers, beginning with the earliest Church fathers, to insist that the eclipse at the time of the Crucifixion had to have been miraculous, as it was not naturally possible, says Smoller. Why? Timing is everything: The Crucifixion reportedly took place during Passover, which begins on the first or second full moon after the spring equinox. But you need a new moon—not a full moon—for a solar eclipse to occur.

Doctors in the Middle Ages needed to know about eclipses, too.

The Robbins Library and RBSCP collections boasts a beautiful “bat book almanac” that is based on the Kalendarium of John Somer from the 1390s. Small and dainty, the parchment almanac was designed to be folded and carried around. As tools for astronomy, prayer, and astrology, such almanacs played a role in a patient’s prognosis, diagnosis, and treatment—the medieval equivalent of a WebMD smartphone app.

“While we see that kind of information in book format frequently, it’s very rare to have this kind of manuscript that was made to attach to someone’s belt so that they could look at it and unfold it while consulting with someone,” says Siebach-Larsen. In fact, there are 31 known almanacs of this type from England in existence, with only four of them—one being the University’s—dating as early as the 14th century. According to Siebach-Larsen, the Rochester manuscript might be one of the earliest English manuscripts of these texts and of this type.

Smoller adds that the almanac was designed to let physicians look up the most auspicious time to mix medicines and undertake medical interventions. And while the manuscript contains information about solar eclipses—along with striking illustrations—it’s not clear if that particular celestial phenomenon was considered a good or bad omen in the medieval healing arts and sciences.

Lunar and solar eclipses were noteworthy in the Middle Ages. But some planetary alignments were the really big thing.

In a hierarchy of astronomical importance, what comes first—lunar eclipses, solar eclipses, or planetary alignments or conjunctions?

For medieval people, even though eclipses are much more visible, other planetary conjunctions were much more meaningful. That’s because for medieval astrologers and astronomers, the sun and the moon are fundamentally two of the seven planets. And according to Smoller, it’s the “slower, outer” planets—Saturn, Jupiter, and Mars—that were considered more significant.

“The really important ones are those special conjunctions of Saturn and Jupiter that occur roughly every 240 and 960 years, definitely not those of the every-20-year variety,” she says.

While the next Saturn and Jupiter conjunction will take place in 2040, to medieval astronomers that one wouldn’t have been very important. Instead, the next particularly significant planetary conjunction—from a medieval perspective—wouldn’t be until the 22nd century.

Either way, if history is any indication, it stands to reason that future denizens of Earth will continue humanity’s enduring fascination with cosmic happenings.

Carefully preserved within the roughly three million volumes in the Ģ����ý’s are a couple dozen rare books that explore astronomy and solar eclipses.

To celebrate the 2024 total solar eclipse on April 8, Melissa Mead, the John M. and Barbara Keil University Archivist and Rochester Collections Librarian, will . Anyone who misses the display can request to see the books at any time.

These volumes, some published more than 500 years ago, can’t be checked out, but they’re still worth checking out. Here are seven titles that offer a taste of what awaits.

Introductorium in Astronomiam by Ja’far Ibn Muhammad Abu Ma’shar (Abumasar) Al-Balkhi (1489)

Astronomer and astrologer Abumasar, who was born in what is now Afghanistan, penned this anthology of his observations of the cosmos between 849 and 850. This copy was printed in 1489 and is one of the oldest of the astronomy books in the archives.

(The Great Introduction to the Science of Astronomy) consists of eight books dealing with subjects as varied as how the planets in our solar system influence Earth and the relations between zodiacal signs.

This treasure was bequeathed to the University by alumnus William Harkness, who made what astronomers consider a “landmark discovery” during a solar eclipse in 1869.

Astronomicum Caesareum by Petrus Apianus (1540)

Holy Roman Emperors Charles V and Ferdinand I commissioned German humanist Peter Apian to complete this work, whose title translates to “The Emperor’s Astronomy.” (The ego of a holy Roman emperor apparently knows no bounds.)

The Ģ����ý’s copy is not an original, but rather a facsimile. It is worth a look, though, because of its intricate and colorful volvelles, a set of overlapping paper disks that the reader can rotate to calculate astronomical information. Volvelles are like a cross between a primitive computer and a pop-up book.

The volvelles of Astronomicum Caesareum rely on the debunked geocentric model of the universe, which places the Earth at the center of it all. But they are nevertheless something to behold.

Institutio Astronomica by Petri Gassendi (1653)

You won’t be able to read this work by French astronomer and mathematician Pierre Gassendi unless you know Latin. But you can marvel at its illustrations of solar eclipses and at how far science—and graphic design—have come in the last 400 years.

Institutio Astronomica was based on a series of lectures Gassendi gave in his day and is considered one of the first modern astronomy textbooks. Very cool.

Also cool: Gassendi made many of his observations through telescopes given to him by Galileo, and in 1631 was the first person to observe and record a special kind of eclipse in the transit of Mercury across the sun.

Young Ladies’ Astronomy by Montgomery Robert Bartlett (1825)

Opening this textbook is as much a trip into the heavens as it is into history.

Underlying the premise of this teaching tool—whose full title is Young Ladies’ Astronomy: A Concise System of Physical, Practical, and Descriptive Astronomy Designed Particularly for the Assistance of Young Ladies in that Interesting and Sublime Study—is the stark reality that astronomy instruction in American classrooms of the early 19th century was typically reserved for boys.

The author wrote in his introduction that he had collected and arranged the materials while teaching a class of girls in 1820 in “elementary studies.”

The book, which was printed in Utica, New York, includes ringing endorsements from Governor De Witt Clinton, and Theodore Strong, a math and philosophy professor at nearby Hamilton College, who wrote: “I do therefore most cheerfully recommend the work, not only to the Young Ladies of our country, but also to all others, and particularly to the instructions of our schools.”

Diagrams of Geology, History, and Physical Geography by James Reynolds (1849)

Tucked inside this simple, blue Victorian cloth folder are 18 hand-drawn diagrams bursting with color on cardstock for display in an educational setting.

“That was your PowerPoint of the day,” says Mead, the University archivist. “They might have been pinned up on the wall of a classroom.”

As the title of the volume suggests, the diagrams cover topics in geology, history, and geography, including the comparative sizes of the planets of the solar system, the changing of the seasons, and, of course, eclipses.

The best part? Four of them are so-called “transparent diagrams,” constructed with cut-outs on translucent paper that, when held up to the light, illuminate the artwork. You won’t need special glasses to safely view these brilliant images, though.

Has the Earth a Ring Around It? by Dr. Frank Gerald Back (1955)

This heartfelt ode to a pal is a must-read for any Albert Einstein enthusiast.

Author Frank Back, an optical engineer known as for his creation of a zoom lens widely used in television and film, dedicated this book to his close friend Einstein, who had helped arrange for Back to “chase” and photograph a total solar eclipse from aboard a military jet in 1955.

Back had intended to tell Einstein all about his journey upon his return, but Einstein died just as Back had embarked for The Philippines to catch the aircraft that was to shadow the eclipse.

“This book is a factual report which shall be printed instead of being told to Albert Einstein,” Back wrote in the introduction. “It all started in Minneapolis on July 30, 1954 5:08 A.M., with a total eclipse of the sun of no scientific significance.”

The book is illustrated with photographs of Back and Einstein, lending an intimacy to the relationship that Back’s words alone don’t capture.

Solar Eclipse Photography for the Amateur by Eastman Kodak Co. (1959)

The total solar eclipse covering parts of the United States on April 8 is an opportunity for amateur and professional photographers alike to capture a celestial phenomenon.

Lots of websites offer advice on snapping a picture of the eclipse, with perhaps the most reliable among them being .

But before the internet and smartphones, there was this handy six-page booklet published by the Eastman Kodak Company of Rochester. The booklet was once ubiquitous, but it wasn’t built to last and went out of print years ago, making intact copies hard to come by nowadays.

Perusing this little number, with its table of exposure times, is a rare chance to glimpse how previous generations of shutterbugs learned to make images of eclipses properly and safely.

The booklet was gifted to the Ģ����ý by the late Charles Carlton, a longtime University professor of French and Romantic linguistics.

Properly protecting your eyes during a solar eclipse is crucial for avoiding long-term damage to your vision. In anticipation of the total solar eclipse happening in Rochester, New York, on April 8, 2024, , a professor of optics and of and an associate professor of at the Ģ����ý, wants everyone to understand the risks involved and how to have a safe, enjoyable eclipse experience.

Zavislan, who studied and currently teaches at the , has devoted his career to studying light, and is an expert in optical system analysis and optical engineering. He explains how the sun’s light affects your eyes, how solar eclipse glasses prevent damage, and why you probably shouldn’t dust off your old eclipse glasses to reuse this April. Along the way, he offers helpful tips to have a memorable viewing experience.

Q&A with James Zavislan

How do solar eclipse glasses work?

Zavislan: Eclipse glasses attenuate, or filter out, the portions of the solar spectrum that could injure the eye. Different spectra of light from the sun have different effects on the eye, and the three most important to block in this case are:

• Ultraviolet—wavelengths we normally can’t see that get us sunburned if we spend too much time outside. This light puts our cornea at risk.
• Visible—in particular the wavelengths that are closer to the blue portion of the spectrum.
• Infrared—wavelengths that you don’t see, but we normally associate with heat.

Eclipse glasses are made of mylar, a polyester film. Historically, that’s what photographic film was made from at Eastman Kodak right here in Rochester, and it’s picked because it is very inexpensive to make and very strong. The outside portion is a reflective metal film, usually aluminum, that’s on a partially absorbing substrate that provides a little bit of additional attenuation as well in case the metallic film gets slightly scratched.

why do we need eclipse glasses? what happens if you look at a solar eclipse for too long?

Zavislan: In general, when we look up at the sun, it’s uncomfortably bright, so our pupils constrict, and at some point, we just look away. During an eclipse, less and less of the sun is exposed, so our instinct to look away is diminished; however, the portions that are still visible have the same brightness as if the moon was not blocking it.

There are two things you worry about from looking at the sun long-term: photochemical changes and heat.

As you stare at the sun, you’ll be putting the most acute part of your vision, called the macula, at risk. While looking at things of interest, you’ll get a cumulative dose of blue light, which causes a photochemical injury, putting chemicals in your eye that can essentially be toxic, and then you’re adding to it a thermal background. Those two together, especially the photochemical effect, can lead to a degradation of your retina.

How do I know if my solar eclipse glasses are good enough?

Zavislan: You want to make sure it meets the standards set by the , or ISO. If you look on the inside of the glasses, you should see an ISO number 12312-2 stamped there.

The final thing that I encourage everybody to do prior to using the glasses is to hold them up to a very bright light and make sure there are not any pinhole defects. These glasses can get damaged. It’s really not a good idea to pull those glasses from 2017 out of the drawer and use them again. They may have gotten scratched or damaged or otherwise have aged. Go with a fresh pair of solar eclipse glasses from reputable source.

Can I take off my glasses during the eclipse?

Zavislan: You should only take them off during totality, when no white portion of the sun is visible. It may be tempting just before or after when there will be bright spots on the edge—they’re sometimes called diamonds or Baily’s beads—but keep your glasses on until you see no portion of the sun.

Can I use my ISO-certified sunglasses to view an eclipse?

Zavislan: Sunglasses are not intended to protect your eye from direct viewing. They could be ISO-certified under a different standard. You only want to look at the sun during an eclipse with glasses that have the ISO 12312-2 standard stamped on them.

Can I use polarized glasses for solar eclipse viewing?

Zavislan: No. Glasses or sunglasses, whether polarized or not, do not sufficiently attenuate the sun’s light for direct viewing during a solar eclipse when any bright part of the sun is visible.

If you are in a region that will experience totality, the sun’s corona will be visible during totality. The light from the corona is polarized and its appearance will change if you view it with polarized sun glasses and tip your head. However, you must remove your sunglasses and resume using ISO-12312-2-rated eclipse glasses immediately at the end of totality.

Can I use my phone to take a photo of the eclipse?

Zavislan: You should not point your cellphone camera up to the sun. First, you’re likely not going to get a good picture. Second, you’re going to be likely in a situation where you’re going to be encouraged to kind of look around your glasses as you’re trying to see your cell phone picture. Not good. And then the third thing is that you’re essentially baking your sensor.

The one time where I would encourage you to try and grab one cell phone picture is during totality. If you have a cell phone camera that can do some level of optical zoom—I wouldn’t bother with digital zoom—you can just take a quick picture. But my strong advice is to not spend a lot of time trying to get a cell phone picture for what should be a wonderful visual memory during totality.

How did the Ģ����ý ensure its eclipse glasses are safe?

Zavislan: We performed additional testing at the Institute of Optics. One of the things we do within our training program is to give the students an opportunity to test optics. This is a priceless chance with the eclipse coming up to show how one would certify these glasses and make sure we’re meeting the standard. It’s also a great chance to illustrate to our students what’s possible using routine equipment that we have at the Institute of Optics.

Is there anything special about the April 8 eclipse that I should look for?

Zavislan: When the sun’s main disk is blocked, there will be streamers of the sun’s corona flowing outward. We’re fortunate that we’re entering what’s called a solar maximum—the sun is nearing its absolute peak of activity—and because of that, there are energetic expulsions almost every week. If we’re really fortunate, one of those coronal mass ejections would be happening right around the time of the eclipse.

There’s no shortage of advice on how to safely view the total solar eclipse on April 8, 2024. From guides on eyewear to telescope filters and vantage points to pinhole projectors, modern media has every angle covered.

So, what advice were people given about how to look at a solar eclipse the last time such an event plunged Rochester into darkness? Before the internet. Before smartphones. Before television. Before eclipse glasses were mass produced.

It was 1925 and Calvin Coolidge became the first president to have his inauguration broadcast on radio, F. Scott Fitzgerald published The Great Gatsby, and the National Spelling Bee debuted.

Here’s a look back at how , the student newspaper that preceded , advised the University community to view the total solar eclipse of January 24, 1925.

1. Make sure your timepiece is accurate.

Before the clocks on our computers and smartphones were synced up to atomic clocks embedded in GPS satellites orbiting the globe, no one really knew precisely what time it was.

People set clocks in rough approximation. They might have asked someone, “What time do you have?” and that person, looking at their wristwatch or pocket watch, might have replied, “Oh, about quarter to 3.” And, so, the time became 2:45.

During the last total solar eclipse in Rochester, wristwatches had just come into vogue, , who affixed their pocket watches to their wrists in combat.

University physics professor Floyd Cooper Fairbanks was a stickler for time in his column in The Campus on how to view the eclipse. “If you have an accurate timepiece, recently checked, it will be worthwhile to record the exact time (of the total solar eclipse),” he wrote. “. . . If you have an accurate timepiece, the exact time of the beginning and ending of the totality should be observed.”

He suggested watching from a high hilltop and to look to the west for the path of totality—a shadow roughly 110 miles wide—fast approaching. “(T)he black shadow may be seen approaching at the tremendous speed of 1,300 miles an hour,” he wrote.

That’s a shadow about the size of Connecticut.

2. Enjoy the spectacular solar corona—but don’t ask what it is.

The last time Rochester was engulfed in a total solar eclipse, scientists had yet to settle on what made the solar corona so spectacular.

“The most striking object to be observed during totality is the corona,” Fairbanks wrote. “. . . There is no satisfactory explanation of the corona. The spectroscope gives evidence that its light is due to solid and liquid particles and luminous gases.”

Thanks to a landmark discovery by Rochester alumnus and astronomer William Harkness in 1869, scientists knew the corona comprised something other than the gases that made up the sun. They dubbed that something coronium.

But it wouldn’t be until observations made during eclipses in the 1930s —albeit with half of its 26 electrons missing. That indicated the corona was many times hotter than the sun itself. Today, scientists are still trying to figure out why.

3. Don’t use your opera glasses to view the eclipse.

There is no telling how many everyday people in Rochester had opera glasses at their disposal in 1925.

What we do know, though, is that the University’s Eastman School of Music and its Eastman Opera Theatre began in 1921, and that Eastman Theatre on Gibbs Street quickly became Rochester’s preeminent performance space upon opening in 1922.

Apparently, opera glasses were ubiquitous enough around campus that Fairbanks saw fit to warn in his column, “The sun should not be looked at through an opera glass or telescope while any portion of it is shining, unless the eyepiece is covered by smoked glass.”

But that bit about “smoked glass” is outdated. Using smoked glass to view solar eclipses had been popular since King Louis XIV of France covered his telescope with a piece of smoked glass to observe an eclipse in 1706. It , when doctors began documenting eye problems in children who used smoked glass to view eclipses.

How to look at a solar eclipse today

Do not attempt to view the upcoming eclipse with any eyewear that are not certified ISO 12312-2 compliant, the international safety standard for solar eclipse glasses. So, if you haven’t already, it’s time to put away the opera glasses, smoked glass, and even that older pair of solar eclipse glasses (here’s why).

Need a fresh pair? The University has you covered. Get yours here.

Mark your calendars for April 8, when Rochester will experience a total solar eclipse. With the city being among a handful of prime viewing spots throughout the country, the Ģ����ý has day-of plans and activities underway. Check out our go-to online resource for everything you need to know ahead of the big day.

When is the next total solar eclipse? What time is the solar eclipse? 

The next full solar eclipse is on April 8, 2024. The solar eclipse starts at 2:07 p.m. and ends at 4:33 p.m., with totality lasting from 3:20 p.m. to 3:23 p.m. In total, this phenomenon will last two hours and 26 minutes.

Can you look at a solar eclipse?

Reminder: Eclipses should only be viewed by watching a projected image of the sun or by using special glasses with protective lenses certified for safe eclipse viewing. Never look at the sun without proper eye protection; even a brief glance can cause permanent damage to your retinas.

Professor Jim Zavislan with the has been scouting locations for people who want to safely photograph the 2024 eclipse. Viewing opportunities for the University community are being planned for the Eastman, Wilson, and Hajim Quadrangles on the River Campus.

• Learn more about protective eclipse eyeglasses, including where members of the University community can get a pair.

Q&A: What you need to know about solar eclipses

Dan Watson, a professor of at Rochester, answers questions about the phenomenon of eclipses.

What is a solar eclipse? What causes an eclipse of the sun?

Watson: A solar eclipse is caused by the shadow of the moon, as the moon passes between you and the sun. The moon’s shadow has two parts: the umbra, which is the central region, and the penumbra, which is the outer region. People in the path of the umbra will see a total solar eclipse, whereas those on the area of Earth where the penumbra passes over will see a partial eclipse. Earth is bigger than the moon’s shadow, so where you’re standing on Earth makes a difference.

How often do total eclipses of the sun occur?

Watson: In any specific place on Earth, about once per 400 years on average.

Why don’t total eclipses of the sun happen more often?

Watson: They can only happen when the center of the moon lays between the Earth and the sun, along the straight line connecting that place on Earth and the center of the sun, and when the moon is relatively near Earth along its orbit. Because the moon’s orbit around the Earth is tipped slightly from the Earth’s orbit around the sun, this arrangement is rare. If the moon is close to its maximum distance from Earth when the eclipse occurs—so that it’s not as large on the sky as the sun is—we get an annular eclipse: a ring of sun surrounding the moon, as was the case on October 14, 2023, and which was as seen from parts of the western US, central America, and South America.

How do we know when eclipses will happen?

Watson: Astronomers have measured the orbits of the moon and planets, and the position and speed of each in their orbit, extremely accurately. With these data, and computers, we can predict with that same degree of accuracy where and when eclipses will occur.

What is it like during a total eclipse versus a partial eclipse?

Watson: During a total eclipse, it becomes like twilight for those two to three minutes of totality. The sun’s corona becomes visible as well as stars and planets, the temperature drops noticeably and animals respond with their normal nocturnal behaviors. Going from daylight to a period of relative darkness during the middle of the day is incredible to experience. During a partial eclipse, the sun will look like a crescent in the sky and the day will get a little darker, but it won’t be as striking as a total eclipse.

How excited should we be about the April 2024 total solar eclipse in Rochester?

Watson: Pretty excited! Although we might need to be concerned about the risk of the eclipse being clouded out. Historically, Rochester skies are clear 51 percent of the time on April 8 between 2 p.m. and 4:30 p.m. April 8, 2023, was a clear, sunny day locally.

Editor’s note: This story was originally published on October 10, 2023, ahead of the partial solar eclipse on October 14 of that year. It has been updated and republished with information about the 2024 eclipse. 

When it comes to studying solar eclipses, Ģ����ý scholars have been at it a long time. Case in point: Alumnus William Harkness, whose observations of the sun’s corona during a total solar eclipse in 1869 have been

At the time, few people had ever gotten a good look at the solar corona—the outermost jacket of gases that make up the sun’s atmosphere. The sun’s blinding brilliance made studying anything in its immediate vicinity almost impossible. Only during eclipses did its radiant halo, the corona, become visible.

In fact, astronomers of the day debated whether the ring of light revealed during an eclipse was the sun’s atmosphere at all. Some thought it was just sunlight penetrating the Earth’s atmosphere. Others speculated it was a lunar atmosphere.

Here comes the sun’s corona

Harkness helped put the debate to rest with his study of a solar eclipse on August 7, 1869, from a hilltop on the outskirts of Des Moines, Iowa, one of the cities in the eclipse’s so-called path of totality.

Vital to his research was his use of a relatively new instrument called a spectroscope, a glass prism that splits light into a rainbow of colors emitted by specific atoms and molecules. The hues act like a key to identifying different elements.

Affixing a spectroscope to a telescope enabled Harkness to observe a continuous green line ringing the sun as the moon slipped between it and the Earth and punched a hole of darkness in the daytime sky.

As documented by the , Harkness concluded that the corona was “a highly rarefied self-luminous atmosphere surrounding the sun, and, perhaps, principally composed of the incandescent vapor of iron.”

“We have succeeded beyond our most sanguine expectations,” Harkness, who was a lieutenant commander and mathematics professor in the Navy at the time, wrote of his research in a telegraph to a colleague.

His missive was widely reported in newspapers across the country, from the in Utah to the in Vermont.

“We have one hundred and twenty-three photographs of the eclipse, two being of totality,” he added. “. . . Could see no absorption lines in the spectrum of the corona. It gave a continuous spectrum with one bright line on it.”

His observations, which he photographed, were corroborated by those of Charles Augustus Young, an astronomy professor at Dartmouth College, who studied the same celestial event from a vantage point of roughly 160 miles east in Burlington, Iowa.

Harkness’s observations would eventually help answer the question, ‘Is the solar corona hotter than the sun?’ 

Scientists hypothesized that the green line might be the emission of a new element of the sun, which came to be known as coronium. They studied that green line during eclipses for the next seven decades before concluding that coronium was not a new element, but rather iron stripped of half of its electrons.

That finding suggested the solar corona was hotter—millions of degrees hotter—than the surface of the sun and has since helped the scientific community better understand how stars work.

Harkness, a member of the Class of 1858, was 11 years on from graduating from the Ģ����ý at the time of his discovery, but he kept his alma mater in mind throughout his life. When he died in 1903, having reached the rank of rear admiral in the Navy, he bequeathed to the University of nautical and scientific instruments as well as his library and papers.

Harkness Hall, which was erected on the River Campus in his honor in 1946 and originally devoted to naval science and training naval officers, today houses the Departments of Political Science and Economics.