spectroscopy – Planet Pailly

Hello, friends! Welcome to Sciency Words, a special series here on Planet Pailly where we take a closer look at the definitions and etymologies of scientific terms. Today on Sciency Words, we’re talking about the word:

CORONIUM

Here on Sciency Words, we usually talk about scientific terms that are relevant and useful in modern science, but sometimes I like to draw attention to scientific terms that didn’t make it. I think it can be helpful to learn about how and why words drop out of the scientific lexicon. So today, we’re going to talk about coronium, a chemical element that we now know does not exist.

Definition of coronium: A chemical element that scientists in the late 19th and early 20th Centuries thought existed based on a mysterious green emission line detected in the Sun’s corona. At least one very prominent scientist (Dmitri Mendeleev) believed coronium to be an element lighter than hydrogen, with chemical properties similar to helium and argon.

Etymology of coronium: In 1869, American astronomers Charles Augustus Young and William Harkness independently detected a green emission line in the Sun’s corona during a solar eclipse. In 1887, Professor A. Grünwald proposed the name “coronium” for whatever chemical substance caused that green emission line. Since this unknown substance was first detected in the Sun’s corona, coronium seemed like an obvious name.

The “discovery” of coronium came right on the heels of the discovery of helium, and the story of these discoveries was eerily similar. Scientists observe a solar eclipse. A strange, new emission line appears in Sun’s spectrum, as measured using a spectroscope. This emission line is (or seems to be) the first evidence of a newly discovered chemical element.

Dmitri Mendeleev was initially skeptical about both helium and coronium, because he couldn’t find places for them in his periodic table of the elements. Toward the end of his life, however, Mendeleev tried to shoehorn these elements, along with several others, into his theories by adding a “group zero” to the periodic table. Each group zero element is lighter than the group one element it sits next to—for example, argon is lighter than potassium, neon is lighter than sodium, helium is lighter than lithium… and coronium ended up sitting next to hydrogen, indicating that coronium is an element lighter than hydrogen.

Mendeleev was a smart man, but he was wrong about group zero. After some reshuffling of the periodic table, most of the group zero elements were moved to group eighteen (a.k.a. “the noble gases”), and in the end, it turned out there really was no place for coronium. No element lighter than hydrogen exists.

So what caused that anomalous green emission line in the Sun’s spectrum? Turned out it was iron. In the 1930’s, German and Swedish astronomers Walter Grotian and Bengt Edlén discovered that a form of super-hot, super-ionized iron gives off an emission line at 530.3 nm—an exact match with the 530.3 nm green emission line found in the solar corona. Without the power of the Sun (or the power of modern laboratory equipment), iron doesn’t get hot enough or ionized enough to reveal that part of its spectrum. As a result, scientists in the late 1800’s couldn’t have known what that strange, green emission line was.

Coronium is a Sciency Word of the past, from a time when the spectroscope was a relatively new scientific instrument and the periodic table was still a work in progress. We no longer need to imagine there’s an exotic chemical element found only in the Sun’s corona, not when super-ionized iron explains that green emission line in the Sun’s spectrum just as well.

WANT TO LEARN MORE?

Here’s an interesting article about Dmitri Mendeleev and his mistakes, including his mistakes about coronium and the “group zero” elements. For anyone involved in science education, this article makes a compelling case about why teaching the history of science is so important, with an emphasis on showing how scientists don’t always get it right on the first try.

I also want to recommend this book, simply titled The Sun. It is full of cool and useful space facts that I had never read about before anywhere else (including the false discovery of coronium). The Sun is part of a series called Kosmos, and I highly, highly, highly recommend this series to anyone who loves space.

And lastly, here’s a link to A. Grünwald’s 1887 paper where he first proposed the name “coronium” for a “hitherto unknown corona-substance.”

Hello, friends!

As you know, I love science. I’m a little obsessed. But there are people who get annoyed or even offended by my obsession with science, and every once in a while one of these people will remind me, sternly, that science can’t explain everything. And you know what? I generally agree with that sentiment. But then people start declaring that science will never know this specific thing or that specific thing, and I immediately think of a certain 19th Century French philosopher named Auguste Comte.

Comte was not some scientifically illiterate buffoon. He wasn’t one of those 19th Century evolution deniers, or one of those latter-day opponents to the heliocentric model of the Solar System. In fact, Comte is regarded today as the very first philosopher of science, in the modern sense of that term, and he gets credit for coining the word “sociology” and for laying the philosophical foundation for that entire branch of science. There’s also a wonderful quote from Comte about the mutual dependence of scientific theory and scientific observation. Basically, you can’t formulate a theory without observation, but you also can’t make an observation without the guidance of a theory.

But that is not the Comte quote I think of whenever somebody starts lecturing me about the things science will never know. It’s this quote about the stars: “[…] we shall never be able by any means to study their chemical composition or their mineralogical structure…” Comte also declared that: “I regard any notion concerning the true mean temperature of the various stars as forever denied to us.”

Comte wrote this in 1835, and if you can put yourself into an 1835 mindset you can see where he was coming from. There’s no such thing as rocketry. We don’t even have airplanes yet. And even if you could fly up to a star (or the Sun), how would you measure its temperature? What kind of thermometer would you use? And how would you go about collecting stellar material, in order to determine the star’s chemical composition?

According to Comte—a highly intelligent and very pro-science person—this sort of knowledge was utterly impossible to obtain. And yet only a few decades later, thanks to the invention of the spectroscope, scientists started obtaining some of this unobtainable knowledge. For those of you who don’t know, spectroscopes separate light into a spectrum. Some parts of the spectrum may appear brighter or darker than you might otherwise expect, depending on which chemical substances emitted or absorbed the light before it reached the spectroscope. And so by comparing the spectral lines of chemicals we have here on Earth to the spectrum obtained from the light of a star, you can determine the chemical composition of that star.

You can also measure a star’s temperature thanks to a concept known as black body radiation. Basically, black body radiation refers to the fact that things glow as they got hotter. If no other light sources are involved, then the color of a glowing object will be directly related to that object’s temperature. Ergo, if you know what color a star is, then you can work out a pretty accurate estimate of what temperature that star must be.

Auguste Comte didn’t foresee any of this. It is certainly true that science does not know everything, and there are surely things that science will never know. But if you think you know, specifically, what science can never know, I question that. Someday, some new invention (like the spectroscope) or some breakthrough discovery (like black body radiation) may turn an utterly unknowable thing into a matter of trivial measurements and calculations.

Maybe the one thing science truly can never know is what science’s own limitations are.

WANT TO LEARN MORE?

Here’s a very brief post about Auguste Comte, what he said about stars, and how epically wrong he was with that one prediction.

Also, here’s a short article about some genuine limitations that science has, like aesthetics, moral judgements, etc.

Tag: spectroscopy

Science Can’t Explain Everything