I suppose I should preface this post by admitting to a bit of bias: as an astronomy nerd, I’m inclined to find any discovery there amazing. But don’t let that fool you – the story you’re about to hear is, arguably, one of the most important scientific insights in history. Astronomy or otherwise. Read on, and be the judge.

It all started, as any good scientific discovery should, with Isaac Newton in 1665. Being the curious soul that he was, Newton wanted to figure out once and for all what was going on with light. One day, Newton darkened his lab completely except for a small hole in his window shutter, allowing a thin beam of sunlight to pass through. He placed a prism in the path of this sunlight and saw the now famous color spectrum (or as many of you may know it, ROY G BIV). The rainbow effects of prisms had been understood well before Newton’s time – but it’s effects had always been attributed to the prism itself, and not the light. Newton believed this had to be wrong.

To prove this, Newton placed a second prism upside down in front of the first. He saw what he had expected all along – the light was split into its component colors by the first prism and then recombined by the second, coming out again as pure white light. He had finally proven that light is made up of all the colors we can see.

Newton’s discovery shed light (pun intended?) on an issue plaguing astronomers of the day. When light is focused in a telescope lens, all colors are focused at different points. This is due to differences in wavelength – for example, red has a longer wavelength, and thus a longer focal length. This leaves a weird red-green aura around everything seen through the telescope. This effect is called chromatic aberration and was one of the main obstacles facing astronomy in the 17th century. Newton’s research had finally given an explanation for this phenomenon.

Fast forward to 1814. Joseph Fraunhofer, a German optics expert, is struggling to produce an achromatic (perfect) telescope lens. In his attempts to measure the exact angle of refraction for all the colors in the spectrum, Fraunhofer decides to examine the spectrum in as much detail as possible. He designs an experiment similar to Newton’s in many ways, with two key differences. First, he used diffraction grating to split the spectrum, rather than a prism, to obtain a greater spectral resoltion. He then used a modified telescope to examine the spectrum in unprecedented detail.

When Farunhofer looked through the lens, what he saw surprised him: a series of thin black lines separated the spectrum. He counted 574 in total, as shown below in a famous drawing from his notebook.

Fraunhofer was delighted with his new discovery – using the lines as definitive reference points allowed him to delineate between the different colors with far greater accuracy. But Fraunhofer was not one to ignore such a quandary: intrigued by these mysterious lines, he set up the first prismatic telescope in 1820 and turned his lens to the stars and planets. He found lines in the spectrum of every star and planet he examined; strangely, these lines were never present in any Earthly sources of light, such as flames.

Sadly, Fraunhofer would never get the chance to solve the problem of his lines, and he would die in 1826 never knowing the full implications of what he had discovered. His research, however, would inspire our last and most important discovery in the long and arduous quest to unravel the spectrum.

Fast forward another 40 years to Gustav Kirchhoff and Robert Bunsen, whose name I am sure anyone who has taken high school chemistry will recognize. Yes, indeed it is that Robert Bunsen, whose invention has been used to burn everything from pencils to hair and arouse the anger of teachers across the world in the process. Before the corruption, however, Bunsen and Kirchhoff combined Fraunhofer’s optical techniques with Bunsen’s improved flame to systematically burn and classify the spectra of eight different chemical elements. They realized that each element gave off a distinct spectrum, unique to that element.

Although the atomic reasons for this effect would not be understood until the early 20th century, Kirchhoff and Bunsen had discovered something incredible: it was possible to determine the chemical makeup of an object simply by analyzing its light.

It wasn’t long before astronomers all over the world were placing prisms on their telescopes to get a look at the spectrum of astronomical objects. Suddenly, humans sitting on Earth had the ability to say, with certainty, what the stars and planets were made of.

This profoundly changed how humans thought about the world. For centuries, it had been assumed that Earth was special – that we were different than all those little pricks of light that dot our night sky. But when we analyze the spectrum of these stars, we find that they are made up of just the same things we find here on Earth – hydrogen, helium, carbon, and other abundant elements.

Interestingly enough, helium had not yet been discovered on Earth at the time of Kirchhoff and Bunsen’s discovery. When scientists examined the spectrum of the sun during a solar eclipse, they found an unaccounted for element they dubbed helium, from the Greek word for the sun, helios. Later, when helium was found on Earth, the name stuck.

The discovery of spectral lines has done more to change our perspective of the world than any one discovery in modern science. It launched a whole new field of study, astrophysics, in which the night sky is studied not for how it moves but how it works. Humans had studied the movement of the skies for years – but they had never dreamed of being able to study its composition and inner workings.

In 1929, Edwin Hubble was able to use spectral lines to determine that the universe is expanding in every direction away from us, with the farthest reaches receding fastest. This helped set the stage for the now well supported Big Bang theory and spawned a whole new branch of astronomy called cosmology, the study of the evolution of the universe.

The realization that we are made of the same stuff as everything else in the universe has taken us one giant leap forward in understanding our place in the cosmos. It has led to our knowledge that the very atoms in our bodies, the atoms that make up you and me and everyone around us, originated in the cores of stars who spread their guts across the universe in great supernovae many billions of years ago. How cool is that? As Neil Degrasse Tyson so elegantly puts it, we are all just stardust.

Without the work of Newton, Fraunhofer, and Kirchhoff and Bunsen, we may still today believe that the stars are holes in the tapestry of the universe, or small campfires in heaven, or even painted features on a sphere that surrounds us. Our modern understanding of the cosmos, and our place in it, owes its origins to the work of these great men and the miracle of spectroscopy. So the next time you look up after a storm and see a rainbow, think of the knowledge spurned by that simple trick of light – and the greatest discovery in the history of science.