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What Can We Learn from Solar Eclipses?

A history of lessons learned and questions still to be answered

Solar eclipses are more than an exciting cosmic phenomenon, they have played a key role in helping humans understand the universe. By observing eclipses, scientists learned about the size and shape of the Sun, the Moon, and the Earth. Eclipses clued-in early astronomers to the orbits of the celestial bodies and how they relate to one another. Copernicus’ theory of heliocentrism cemented the understanding that solar eclipses occur when the Moon passes in front of the Sun. And just like that, public perception of eclipses shifted from a frightful darkening of the skies to an opportunity to learn more about the cosmos.

Studying the Corona

One of the first great modern discoveries surrounding an eclipse occurred in 1868. French solar physicist Jules Janssen discovered a new element while observing the Sun’s chromosphere through a prism. Astronomers named the element Helium, after Helios, the Greek god of the Sun. It would be more than 25 years before helium was discovered on Earth, but we now know it’s the second most common element in the universe.

Janssen was neither the first scientist nor the last to study the outer atmosphere of the Sun during an eclipse. A solar eclipse offers a unique chance for scientists to view the Sun’s corona. “Most of what we know about the corona is deeply rooted in the history of total solar eclipses,” Lina Tran wrote for NASA Goddard. “Before sophisticated instruments and spacecraft, the only way to study the corona from Earth was during a total eclipse, when the Moon blocks the Sun’s bright face, revealing the surrounding, dimmer corona.” An instrument called a coronagraph can mimic eclipse conditions on a telescope, but eclipses still remain the most authentic way to study the corona from Earth.

The Coronal Heating Problem

Scientists thought they discovered yet another new element in 1869 as they observed an eclipse through a spectrometer. A spectrometer helps scientists determine which elements compose a band of light, but the green line that appeared in 1869 didn’t correspond to any known element. Scientists briefly called the new “element” Coronium, but Swedish astronomer Bengt Edlén later determined that the element was superheated iron.

The extreme temperature of the iron indicates that the corona is 2 million degrees Fahrenheit — nearly 200 times hotter than the surface of the Sun. This phenomenon is known as the “Coronal Heating Problem.” The layers of the sun typically become cooler and less dense as they move outward from the core, so scientists are not sure why the corona would be significantly hotter than the surface below it. Heliophysicists believe this may be caused by wave heating, or perhaps nanoflares, but further study of the corona is necessary before we know for certain.

Solar Winds

The corona is full of other fascinating features. Eclipses give astrophysicists a good look at the behavior of loops, streamers, and coronal mass ejections. They are also an opportunity to learn about solar winds: charged particles that emanate from the corona. Solar winds are important in that they define the boundary of our solar system and protect us from cosmic radiation. On the downside, they can disrupt our satellite and GPS-based communications. During an eclipse, researchers can take more accurate temperature readings of solar winds. Interestingly enough, solar wind temperatures do not seem to fluctuate in tandem with the solar cycle. It’s another mystery that may require more solar eclipses to solve.

The Earth’s Ionosphere

Eclipses don’t just tell us about the Sun. We can also learn more about our own atmosphere here on Earth. The ionosphere is the upper level of the Earth’s atmosphere. During the daytime, the ionosphere is “charged” because “energy from the sun and its corona feed extreme ultraviolet photons into this area, creating free electrons and ions,” physicist Phillip Erickson told Slate. The ionosphere is less active at night. An eclipse is like a light switch for the ionosphere, turning the charge off and back on again as the Moon passes in front of the Sun. This allows scientists to study changes in real-time, and can provide clues about how the ionosphere affects communications and space weather.

Studying Other Structures

Eclipses also offer insight into other structures in the solar system. Some scientists have used the occasion of an eclipse to take more accurate thermal readings of Mercury. Others have embraced eclipses as a model that makes our stratosphere more “Mars-like.” During an eclipse, UVA and UVB levels in our upper atmosphere more closely resemble those on Mars, allowing researchers to test microbial responses to Mars-like conditions.

An eclipse also led to one of the most important “proofs” in modern science — a test of Einstein’s Theory of Relativity. Einstein’s theory posited that light shifts as it passes by a massive body (like the Sun). In 1919, researchers noted that the light from stars shifted before, during, and after a total solar eclipse. It appeared that Einstein guy was right all along.

Studying Life on Earth

These days, instruments like the Parker Solar Probe are teaching us about the Sun (and other structures) in ways we never imagined. But that doesn’t mean the days of learning from eclipses are through. Eclipses present a unique opportunity to learn about changes in our solar system. And some of those changes occur right here on Earth.

During the Eclipse Soundscapes: Citizen Science Project, we’ll be studying how life on Earth responds to those changes. Anecdotal evidence suggests that we could experience altered animal behaviors and sounds (for example, nocturnal animals calling during the eclipse, or diurnal animals producing a “false dawn chorus” as the light re-emerges). We’ll be taking soundscape recordings before, during, and after the eclipse. Then, we’ll analyze the recordings for any patterns or anomalies. Interested in joining us? Sign up here to be a part of the project!

by Kelsey Perrett

The Science of Soundscapes

What is a soundscape?

Have you ever listened to an album of relaxing nature sounds, like rains falling or whales singing? That’s a soundscape! Soundscapes include any noises that humans hear in a given environment.

There are three major types of sound that can be found in soundscapes:

Biophony: Sounds generated by organisms (like bird song and cricket chirps)
Geophony: Sounds generated by the non-biological natural world (like wind and water noise)
Anthropophony: Sounds generated by humans or human-made technology (like human voices or vehicle traffic).

The study of soundscapes encompasses several disciplines, including acoustic ecology, bioacoustics, and soundscape ecology. The Eclipse Soundscapes Project focuses primarily on soundscape ecology.

What can we learn from soundscapes?

Soundscape ecology is an emerging field (established in 2011 by the article “Soundscape Ecology: The Science of Sound in the Landscape”). Scientists are still learning about the many ways it can be useful. The purpose of soundscape ecology is to explore the relationships between living organisms (including humans) and their environment. Soundscape ecologists use recording devices to collect soundscapes, then analyze the results using a spectogram: a visual representation of how sound frequencies vary over time.

Soundscapes themselves are valuable to conservation. There is a push to preserve soundscapes in delicate ecosystems, since changes in climate or excessive human impact may cause soundscapes to alter or disappear. Some agencies, like the U.S. National Park Service’s Natural Sounds and Night Skies Division, are working to protect soundscapes by collecting recordings and preserving acoustic environments.

The analysis of soundscapes can also be beneficial to science. Acoustic data tells us about the environment, its health, and how different species behave and interact within it. We can make simple observations about which life forms are present in a habitat, and when they are most active or vocal.

We can also form hypotheses that explain why animals behave in certain ways. Some research has shown that organisms will change their call’s timing and/or frequency so as not to interfere with other sounds in their physical environment. For instance, some frogs communicate their territorial calls using high frequencies. This may be a natural adaptation to their habitat, where the low frequency sounds of running water are prevalent. Other behavioral changes may happen in response to anthrophony: some birds will adjust their songs in environments where there is a lot of human-generated noise.

Soundscape ecology overlaps with sensory ecology, which focuses on how and why organisms gather information from their environment. Some organisms take advantage of soundscape noise to navigate or to hunt, while other organisms may take busy auditory signals as a sign of danger. From this data, we can research not only how ecosystems impact soundscapes, but how soundscapes impact ecosystems.

Another benefit of soundscape research is that it encourages interdisciplinary and cross-disciplinary study. Ecologists, social scientists, engineers, astrophysicists, and musicians have all turned to soundscapes to help broaden their field of research.

A soundscape ecologist takes a recording by a river. — A scientist captures a soundscape using an audio recording device. Credit: Till Bovermann/CC BY-SA 4.0

Are soundscapes the same as sonification?

Soundscapes and sonification are not the same, but they are somewhat related!

Sonification uses audio to convey information or perceptualize data. There is a lot of great work currently being done in the field of sonification! For example, our friends at NASA’s Chandra X-Ray Observatory have used data sonification to turn the light from astronomical images into sound. Think of it like translation. Sometimes we are limited in our ability to see scientific data, but if we translate it into another medium like audio, we may be able to hear it. And because auditory perception has some advantages (in that it allows us to perceive temporal, spatial, amplitude, and frequency information) it may help us understand the information even better.

One major advantage of data sonification is that it opens doors for people who do not learn visually, including people with blindness or vision impairments. This is also true of soundscapes!

What is an Eclipse Soundscape?

The Eclipse Soundscapes Project will explore how celestial events, like eclipses, can impact life on earth. By collecting and studying soundscapes prior to, during, and after eclipses, we hope to better understand how eclipses change human and animal activity. There is some anecdotal evidence that the changes in light an eclipse causes may influence animal behavior. For instance, nocturnal animals may stir when it starts to get dark, and diurnal animals may vocalize as the eclipse passes and the light returns — this phenomenon is known as a “false dawn chorus.”

These accounts are anecdotal, and to date there is little scientific evidence to prove or disprove these occurrences. By recording a variety of soundscapes and analyzing spectrograms, our scientists hope to identify trends in animal behavior.

To do so, we’re working with a bioacoustic advisory board, featuring some of the top specialists in soundscape ecology and related fields. Our board members include Dr. Megan McKenna of Stanford University’s Goldbogen Lab, Dr. Bryan C. Pijanowski of Purdue University’s Center for Global Soundscapes, Dr. Laurel Symes of The Cornell Lab of Ornithology’s Center for Conservation Bioacoustics, and Sound and Light Ecology Team Research Associate Dr. Jacob Job

We’ll be introducing the team and their work in future blog posts, so stay tuned!

by Kelsey Perrett

Will Wildlife Sound Off during Eclipse 2017?

Birds suddenly stop singing, insects return to their nests, and creatures of the night sound off in the middle of the day. It’s easy to see why solar eclipses once elicited premonitions of doom. But scientists believe there is more than superstition to these changes in animal behavior, and with the August 21, 2017 eclipse, researchers hope to study exactly how and why they occur. That’s why Eclipse Soundscapes has partnered with the National Park Service, Brigham Young University, Idaho, and citizen scientists across the country to record audio data as the eclipse progresses.

Using high-quality recording equipment, including binaural microphone arrays which simulate human hearing, Eclipse Soundscapes will capture audio in a variety of biologically diverse environments, including 15 national parks in the path of totality and two more that will experience a partial eclipse. Audio samples will be taken the day before, the day after, and the day of the eclipse in order to understand how soundscapes fluctuate as the moon blocks out the sun’s light and heat.

“It is clear that animals do respond to the eclipse,” Dr. Kurt Fristrup of the National Park Service said in a press release. “The question is going to be: how much of that response is detectable acoustically? We could see dramatic changes. Past research has studied individual sites during an eclipse, and minor papers have been published, but no one has looked at this phenomenon on a continental scale.”

It is difficult to know exactly what to expect, since most reports of animal sound during an eclipse are purely anecdotal. The last scientific study on the topic was completed by the Eclipse Behavior Committee of the Boston Society for Natural History 85 years ago, surrounding the August 1932 eclipse in Maine, New Hampshire, and Northeastern Massachusetts. In the study, the committee asked citizen scientists to report observations on animal behavior in their location.

The response was overwhelming. Observers reported that birds stopped singing, ants busily carrying cargo stopped and remained motionless, bees returned to their hives, and fish surfaced, while crickets and frogs erupted in a chorus. When the sun re-emerged, birds began a dawn chorus.

In general, it appeared that with the darkening of the sun, diurnal animals settled into their dusk routines, while nocturnal animals stirred to action.

Of course, it is impossible to make generalizations about an entire species based on the actions of individuals in an isolated area, but some of the species — such as the crickets and frogs, responded to the eclipse in unison, producing a much more measurable response. It is possible that these creatures respond more to an eclipse because their behaviors are dictated by light, as opposed to the circadian rhythms which produce sleep/wake cycles in creatures like humans.

That’s not to say “higher” mammals are unaffected by an eclipse. A report of a 1984 solar eclipse by the American Journal of Primatology reported that chimps at the Yerkes Regional Primate Research Center congregated on their climbing structure and oriented themselves in the direction of the eclipse. One juvenile chimp reportedly stood upright and gestured in the direction of the eclipse.

Humans respond to eclipses with comparable excitement (just do a quick social media search for #Eclipse2017 to see how much buzz the August 21 eclipse has generated). For this reason, Eclipse Soundscapes is not limiting audio recording to wildlife areas. Urban areas, where human reactions to the eclipse can be studied, are of particular interest to sociologists and anthropologists. In that regard, the eclipse is a perfect chance for humans to study ourselves, and where we fit into our ecosystem and the greater universe.

All recordings from partners and citizens scientists will be collected and hosted in a database on EclipseSoundscapes.org. This database will be free and open source so that researchers, educators, artists, anyone else who is interested can access and listen to these soundscapes.

by Kelsey Perrett