Happy Vernal equinox heathens! If you are fortunate enough to live in a part of the Northern Hemisphere with minimal light pollution, you can see a night sky filled with constellations. Some of the lights twinkling in the night sky are stars and planets, but some of the dots are entire galaxies billions of light years away. If one views the night sky under the right conditions, the cosmos looks like a grand work of abstract art, full of mystery and wonder. Our understanding of the universe has grown quite a bit in the last five hundred years and as our understanding of the universe has grown more sophisticated, we humans have become a smaller and smaller part of the universe. It’s a necessary and inevitable consequence of our mental, emotional, and spiritual development.
At the start of the nineteenth Century, a German scientist named Joseph Fraunhofer had stumbled upon a discovery Sir Issac Newton had made years ago. Newton had been studying sunlight, refracting it through a prism to reveal light from our Sun was made up of a spectrum of colors. The prism was able to split light up into the its constituent colors because the material allowed each different wavelength of light to move through the material at a different speed, revealing a rainbow. Fraunhofer was studying this spectrum when he noticed darker lines broke within the Sun’s spectrum and appeared to pop up in specific wavelengths of light. He meticulously recorded these dark lines within the spectrum where light wasn’t emitted but rather absorbed and the spectrum went black. Stars emit light at all frequencies in their core where fusion occurs; molecules, atoms, and ions that may be present near the surface of the star will absorb that light strongly at unique frequencies. Thus, the observed spectrum of stars will contain relatively dark bands at those characteristic frequencies of the constituents of the outer layers of that star.
This curiosity didn’t go unnoticed. Years later the scientists George Kirchhoff and Robert Bunsen were subjecting the periodic elements to high temperature until each element when put under a flame hot enough would give off a bright flame. Most interestingly, each element they tested gave off light at a different wavelength when heated. They soon realized that the wavelengths of light that some of elements they were studying matched the wavelengths in Fraunhofer’s absorption lines. Where Fraunhofer found that light was being absorbed that those wavelengths, Bunsen and Kirchhoff found that light was given off at these wavelengths. Still, it was easy to note that these two mutually exclusive phenomena in both their experiments were appeared at the same spots on the light spectrum. Bunsen and Kirchhoff soon surmised that the Fraunhofer lines represented elements present in the Sun’s atmosphere. These absorption lines are detected in the spectrum when specific elements absorb photons at specific wavelengths.
This assumes that the object being studied through a spectrometer is stationary relative to the observer. When the object is moving, though, the light coming from that object like a planet or a star ends up getting shifted depending on whether the object is moving closer to or farther away from the observer. When the object moves closer to the observer, the light coming towards the observer is scrunched and the wavelength of the light decreases, so that we observe the light with a bluish tint, blue light having the shortest wavelength in the visible spectrum. When the object is moving away from the observer, the light gets stretched out and the wavelength of that light tends to appear to us as redder. This shift in color is a direct consequence of the Doppler Effect. An indirect method for finding extrasolar planets involves using the Doppler shifts in the spectrum of the planet’s parent star. When a massive planet like Jupiter is close enough to its parent star, it can actually cause the parent stars orbit to wobble. Scientists using high-resolution spectrometer can detect the wobble of the star as it lurches towards or away from Earth. Knowing this, scientists can calculate the mass of the planet based on how much its star is wobbling.
When scientists point a spectrometer at a star, they are able to gain valuable information about that star’s composition, temperature, luminosity, distance, density, mass and relative motion, too. We know that the hydrogen and helium in stars fuse into heavier elements. Paradoxically, older main sequence stars tend to be hotter and brighter than younger stars and older main sequence stars tend to be made of more than just hydrogen and helium. This is because stars do not burn like a campfire or blowtorch; fusion is a nuclear And because of this, stars get brighter because gravity pushes down on the star, concentrating the nuclear reactions going on inside of it. This causes the rate of nuclear reactions inside the star to increase. This tug of war between gravity and fusion will allow the star to remain stable, but once the star starts running out of nuclear fuel, gravity starts to win, pushing the star into a smaller and smaller area until the star can’t take it anymore and it explodes in a nova. During these violent events, some bright enough to light up the night sky, heavy elements are flung out into the interstellar void. Astronomers can see all of this using spectrometers and can actually sniff out the different elements that are being forged in these cataclysmic events.
Astronomers don’t limit their use pf spectroscopy to stars and planets; they can focus this tool on galaxies. When astronomers point a spectrometer at a faraway galaxy, they are collecting data on a collection of the brightest stars in that galaxy. When astronomers first began using spectrometers to look at galaxies, they found some weird looking absorption spectra coming off of these distant objects. At first, astronomers called them LGM’s, a tongue-in-cheek for Little Green Men, thinking this unusual phenomenon was a sign of extraterrestrial intelligence. Later on, these objects were renamed quasi-stellar radio sources, or quasars. We now hold that quasars are galaxies so distant from us that their light must be incredible in order to be seen from so far away. This light has been redshifted to the point that they were giving off powerful radio signals. Doppler effect doesn’t just effect the light coming off of galaxies, though. Fritz Zwicky found in a study of the Doppler shift that most galaxies were moving away from our galaxy much faster than seemed to be possible. Zwicky hypothesized that in order to account for the increased speed of galactic acceleration that there must be a tremendous amount of matter that can’t be observed or measured in these galaxies. We now believe that this dark matter actually makes up a quarter of our universe and its origin and properties are perhaps some of the greatest mysteries physicists face today.
I would like to end this post with a discussion of the emotional and spiritual implications of spectroscopy; we are insignificant. In Fraunhofer’s time, humans thought that the Earth was in the center of the galaxy and that the galaxy was the entire known universe. As our knowledge peeled back the nature of the cosmos we realized that not only was our planet not in the center of the galaxy, nor our galaxy the only galaxy in the universe, but that the ordinary matter that we’re made off accounts for a tiny fraction of the mass of the known universe. We are a stain on the otherwise pristine universe; a universe made almost entirely of a dark matter and a dark energy that we cannot detect. The notion that a benevolent Creator made an entire universe for us, almost all of it completely inaccessible and undetectable while granting us a tiny island of life on a rock rolling around in the thin veneer of the ordinary matter we’re familiar with is laughable. We are so incomprehensibly insignificant to the universe and yet I am filled with awe that the complexity and scale we see around us arose on its own. Just imagine what we can do knowing that we and we alone possess the ability to etch out our own meaning for existence on the largest canvass imaginable.