Month: August 2021

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!