Splitting Sunlight - The 2021 Summer Solstice

Stars Above Haleakalā

What comes to mind when you think of summer? Our long days and short nights around the summer solstice may mean less time for stargazing, but there are secrets to unlock even in our Sun!

Join Ranger Laurel on a crash course adventure through solar astronomy. Hear about the legends we tell, the science behind our knowledge, and the data of our universe locked up in something as simple as a beam of sunlight.

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TRANSCRIPT:

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Aloha, kākou. It's Ranger Laurel again, back with another “Stars Above Haleakalā” podcast. Today's podcast is going to address the elephant in the room—the star that's such an obvious force in our lives that we often forget that it's a star at all. I'm talking, of course, about our sun.

As always, please be respectful of those around you when you listen to this. If you chose to listen to this in a public place, use headphones to avoid disrupting those around you. Remember to use Leave No Trace principles wherever you are, from your local playground to your national parks—leave wildlife and plants alone, pack out any trash that you bring in, and respect your fellow visitors.

This podcast is intended to be listened to on Sunday, June 20th, 2021. This particular day happens to be the summer solstice for the Northern Hemisphere, which is the longest day of the year. Of course you can listen to it any day, but if you haven't taken the time to sit out in the early morning or late afternoon, I highly encourage it. The sun rises every single day; by most standards it defines a day itself. It is both commonplace and significant—we turn towards it again and again, but rarely do we sit out to appreciate it. I'm here today to make the argument that it is very important to appreciate our Sun. While most folks think astronomy is something that can only happen at night, a huge amount of effort goes around the world in to solar astronomy and studying our Sun, which is good because it turns out the sun is a lot more than a blinding disc in our sky. I could do a whole podcast series just about our sun, but that's a lot of ground to cover (93 million miles, to be precise). So to start things off, I want to talk about the obvious thing that our sun provides us, because it turns out that this simple thing is much more complicated than we ever could have guessed: sunlight.

[Introduction music]

We humans have known from time immemorial that light is hard to define but crucially important. Light drives in the broadest sense our ecosystems, economies, and cultures. But for a long time we struggled to unravel its mysteries. But let's start with the basics, first.

Your garden variety sunlight, the sunlight you're hopefully enjoying right now, is white light. The first thing that makes light tricky is how it gets different colors. For example, we all know that if you mix paint together, like red paint and blue paint, you mix them together, you get purple. If you mix in some green with that purple, you'll start to get a weird mud color. We all know the more colors of paint you add, the darker and muddier your end result will be. Light is the opposite. Mixing together all the colors of light creates white light, not darkness. This is called additive color mixing, and it has no bearing on what we're going to talk about today so don't worry about remembering it. Just know that white light is the combination of all colors. If you're interested in learning more about additive color mixing, you can look it up. It's pretty cool.

The point of this color mixing experiment is this: white light, can be helpful, but its often too much. When science really began digging in to sunlight was when we began splitting the sunlight into its spectrum. What exactly is its spectrum? That answer is easy. In this instance, spectrum is just a fancy word for “rainbow.” You're gonna hear me use those two words pretty much interchangeable throughout the course of this podcast. And that's where our story gets interesting.

Rainbows may be kinda sappy or cliché, but they’re also extremely interesting for scientists. In the simplest terms, rainbows are light broken down into its visible component parts. Most of us know that a rainbow is something we might see in an odd reflection, or arcing overhead after a rainstorm. Most of us also probably know that the rainbow goes from red all the way through violet. . A rainbow is a pretty, corny, pretty corny thing. So if I were to hand you a prism to cast a rainbow, and tell you to use it to divulge the deepest secrets of the universe, you might consider that an impossible task.

But believe it or not, the humble rainbow, a product of split sunlight, was actually the key to cracking significant astrophysical challenges. From the rainbow, we are able to identify the atomic makeup of stars billions of miles away. We developed technology so essential to our lives today that you’ll find it in your dentist’s office. In fact, we began to better understand the fabric of space-time itself. Think you can do that all with a rainbow, sunlight split six ways through a prism? Sounds like an impossible task. But our world is all about impossible tasks. So let’s dive in. [Brief static.] Laurel: TEst... Okay, um, so could you tell me your version of the Māui story? Kuaola: Okay. So long ago, the sun traveled much too quickly across they sky. Sara: It moved way too quickly. Chris: And one of the things that is a consequence of this is that Hina, the mother of Māui, isnʻt able to dry her kapa cloth. Kuaola: Drying is an important part of the kapa making process, so, making things difficult. Chris: And, so, Māui wants to right this so he goes to the top of the Haleakalā. Kuaola: Climbed all the way to the top of Haleakalā. And with one foot on Puʻukolekole, which is not the site of the Haleakalā Obervatories, and his other foot the top of Hanakoʻopiʻi, and their two miles apart, he stood atop the mountain and thatʻs where he snared the sun. Sara: Māui used rope to snare the sun at the top, and hold it in place. Um... they had a long conversation about it... Chris: and he convinces the sun that he should slow down. Sara: Other version say that he actually ripped off some of the sun's rays, in order to make the sun move slower, and it all just depends who's telling they story whether or not he ripped off those rays. Chris: And because of this, that's why we have the days that we have, the heat that we have, and the people were able to do all the work they needed to do. Hina and the people in Hawaii were able to dry their kapa cloth. Laurel: Great, that's perfect! Thank you so much!

[Music builds.]

The story about Māui is an important one for Haleakalā. After all, according to the story, right here on our crater edge is where he came to accomplish his feat—a seemingly impossible task to slow the sun's movement through the sky. You could ask anyone on the island of Maui to tell you the story, and you would get a different version every time. But one thing is always true: he will always attempt to snare the Sun, and he will succeed. In a way, you have Māui to thank for today of all days—he snared the sun, convinced it to slow down, and that brings us to the longest day of the year, our summer solstice.

For the longest time, the Sun was an inscrutable force in our lives. Early solar astronomers rigged projections of the sun, just to be able to make out any details on what appeared to be the sun’s surface without blinding themselves. And today there is a network of solar telescopes trained on the sun around the world. We have come a long way to see past the glare and begin to study our closest star in earnest. However, we still contest with significant challenges.

[Music notes]

One of the most advanced solar telescopes is the world sits next door to Haleakalā National Park. The Daniel K. Inouye Solar Telescope has taken some of the most detailed photos of the sun to date. It works its magic with a mirror that’s 4 meters--that’s 12 feet—wide. Plenty of telescopes have components that are larger than this, but the subject matter for the Inouye telescope presents unique issues. Remember how the kid in your recess (maybe it was you) used a magnifying glass to focus sunlight and set paper on fire? The lens of that magnifying glass that was hot enough to ignite paper was maybe two or three inches across. Now imagine the intensity of sunlight being captured by a mirror 12 feet across. That is some serious heat.

In order to combat the intense power of its subject, the Inouye includes a variety of cooling methods and safeguards. The telescope was designed with seven miles of pipe running through the observatory that deliver coolant to the system. The various mirrors themselves are also cooled, and a specially chilled metal donut eliminates about 95% of the heat from the incoming sunlight, before it affects the system. That’s a lot of engineering dedicated to beating the heat, and the painstaking research that goes into these cooling logistics is what makes the telescope operational. Today, we have it down to a reasonable science, but it hasn’t always been that way.

This problem of heat has plagued solar astronomers for as long as they've been pointing telescopes at the sun. So we're going to step back from the Inouye for now, and instead look back in time, and the very start of solar astronomy.

[Music break.]

OKay, so: The year is 1800, and astronomer William Herschel is confronting a safety issue. While the rest of Herschel’s astronomy colleagues are obsessed with creating star charts to improve navigation, Herschel has been nursing a fascination with our Sun. He faces a similar conundrum as the Inouye solar telescope—how do you study something that puts off such intense energy that it can crack the mirrors of your instruments and permanently blind you? Herschel begins experimenting with different colored glass filters, hoping to find one that reduces the intensity of the light and heat being focused by his telescope.

He comes to the conclusion that different colors transmit heat and light differently. For instance, red tinted glass stopped the glare but cast intense heat on the viewer’s eye—not ideal. By contrast, green glass stayed cool but allowed too much light through to be a viable telescope. This intrigued Herschel, and he set about designing an experiment to test the temperatures of different shades of light. And this is where that famous rainbow comes in: using a prism in a window to split the sunlight into the color spectrum, Herschel set about testing the temperatures of the rainbow, one color at a time.

As Herschel moved his thermometer along the spectrum, from one sliver of color to another, he noted something that seems obvious now: the light towards one the end of the spectrum—violet and blue—was the coolest in terms of temperature, and as he slowly moved the thermometer up the rainbow, the temperature steadily increased. Red light—on the opposite end of the spectrum, was the hottest. Herschel repeated this experiment a couple of times, and began using a secondary control thermometer, to make sure he wasn’t just documenting the rising ambient temperature of the room. Comparing his rainbow results against his control thermometer proved his theory that different colors of lights are associated with different degrees of heat. But what was truly groundbreaking about this experiment was a serendipitous moment after the initial experiment was done. After documenting the rising temperatures of the rainbow colors, on a whim Herschel moved the thermometer one more step up the spectrum—out of the red light and into what appeared to Herschel to be simply the darkness of the room. To Herschel’s amazement, the mercury in the thermometer continued to climb, as if some invisible heat source, even more intense than the red light, acted on it in a way he could not see.

In fact, Herschel had just discovered what we now know of as “infrared” light—light that we cannot see, but which acts upon our world in significant ways as heat. This story marks an historic moment in the study of light, heat, and the eventual discovery of the electromagnetic spectrum, which today drives much of our understanding of our world and the greater universe. This idea—that there is light that is invisible to us—is what eventually leads to the discovery of ultraviolet light, which I hope you are protecting yourself from as you sit out in the sun. It establishes the spectrum that runs all the way from radio waves to gamma waves: in truth, that beautiful rainbow from a prism represents only the tiniest section of the actual “light” out there. Everything from radio communication to x-rays became possible, when Herschel moves the thermometer into the dark unknown next to red light and revealed the unseen yet omnipresent nature of energy.

But when Herschel made this discovery, people struggled to accept the implications—how can you study something you can’t see or hear, or even barely feel? How can light be invisible to us? It was too mindblowing, and at the time it led to extremely flawed conclusions about the natural world. Much of the success of the scientific process depends on being willing to let go of assumptions when confronted by unyielding evidence, and that willingness can sometime take a little while to develop. Herschel’s discovery was a baby step, a challenging but necessary one.

[Music notes]

The resulting fixation on prisms and rainbows, however, would lend itself to another important discovery, which molds astronomy to this day. Around the same time that Herschel is understanding the infrared and invisible light of our Sun, other scientists are noticing bizarre anomalies in the sunlight's spectrum itself. Joseph von Fraunhofer, a young glassmaker, could not shake a particular feature of the rainbow: with a good enough prism, within the split sunlight he could identify vertical black lines, shadows, interspersed at random through the smooth continuum of one color to the next. You can picture, like, a rainbow barcode, stretching again from violet to red, with black lines of varying widths interspersed throughout. Fraunhofer meticulously documented the placement of these lines, and realized no matter the prism, no matter the day, the sunlight split into the same pattern without fail. With a good enough prism, you can see these lines, known as Fraunhofer lines, to this day. What was more curious, using specialized glass more precise than a prism, he could split the light from distant stars as well—and the resulting rainbows of those stars also had these mysterious black lines, some that matched those of the Sun, and some that landed in very different spots. Different stars had different barcodes. [Music building] Like Herschel’s infrared discovery, understanding the significance of these lines took decades of experimentation and discussion. Pursuing the relationship between color, spectra, Fraunhofer Lines and energy, scientists realized that established elements, like sodium and copper, caused flames to turn different colors when they were burned. Returning to our friend the prism, enterprising scientists vaporized various elements, and split the resulting colored firelight through a prism, and discovered a bizarre and exciting inverse of the sunlight spectrum: instead of a complete rainbow with dark bars, elements vaporized in flames exhibited a dark spectra with a few brightly colored bars interspersed throughout—a sliver of teal, some ways away from a strip of scarlet. In essence, each element, when heated to a gas, emits light that can be split through a prism to reveal a unique “fingerprint” of colored lines. Hydrogen has a unique set of colored lines; sodium has a different set, and copper does too.

Well, it didn’t take long to put two and two together: the bright bars present in the spectra of the elements line up with the dark bars in the spectrum of sunlight. Scientists realized that every element will absorb its particular slivers in a continuous spectrum. All of these Fraunhofer Lines that we detect in sunlight’s spectrum are actually giving away the elements that are vaporized around the sun—by matching up the elements bright lines against sunlight’s dark lines, we can identify each element present in our sun.

The physics of this get complicated very quickly, and the rules that dictate these particular reactions, are part of Kirchoffʻs Rules, are worth a look if you’re wanting to take a deep dive into how this works and how we know.

THe bottom line is this is the beginning of a field called spectroscopy (say that five times fast), studying the absorption and emitting spectra of elements to delve into chemical realities. [music building] What is so crucial about this discovery of sunlight barcodes and elemental keys is that the only thing we needed to be able to understand the components of far-off space stuff is light, which is very good at crossing the great expanse of our universe. If we can see it, we can understand what it is made of.

Using spectroscopy, we now know that the element gold is present in trace amounts the atmosphere of our sun, in a vaporized form, because we see the shadows of gold's known barcode present in our split sunlight. And if you have ever wondered how we know what kinds of elements are out there—how can we prove that stars throughout our galaxy are made up of hydrogen, considering we have never visited a star, never mind gotten close enough to one to sample its chemical composition—this is how. Spectroscopy, the harnessing of spectra, light, and shadow, to unlock our Universe. Tell your friends. And thank your nearest rainbow.

[Music crescendos.]

I sometimes... often, wonder how people way in the future will perceive our “breakthroughs.” Like, waaaay in the future, what will we make of these moments? I think about what makes Māui a myth, and Herschel a scientist, and I wonder if time plays more of a roll than we realize. I think about our descendants telling of the legend, “How Herschel Split the Sun,” ages from now, maybe as we bask in the light of a remote star as intergalactic travelers. That sounds ridiculous,like too far off, and impossible. But in the bright light of day, I find that “impossible” turns out to be a relative term. [Music notes.] I hope you can forgive me for finding solace in our myths about tackling impossible problems. I think I'm drawn to these stories because as a park ranger and a citizen of this Earth, I realize I am in the thick of a lot of impossible-seeming problems. Here in Hawaiʻi, we battle the extinction of unique species at an accelerating rate. We see smoke drift over, all the way from California, and we watch our coral reefs lose their rainbow of colors, bleaching to a ghostly pale as ocean temperatures warm. Climate change feels like an impossible problem, a mountain that keeps piling on—where is our Māui, to set things right again?

Well, Māui may have been demigod, but it was his actions and deed, rather than his superpowers, that we tell each other about today. With that in mind, anyone of us can feel empowered to take action for the things that matter: to stand up for our communities, find creative solutions, think through impossible tasks. Same as Herschel, who wanted to stare at the sun. Herschel died well before anyone thought they could create a telescope like the Inouye for solar observation, but the two live on the same continuum of baby steps, and sharing what we know.

This story does not end in the past with a clean resolution or on some distant summit far from your grasp. Every one of us can experience the everyday phenomenon of sunlight, the heat it provides or the light it offers, and what's more, thanks to the electromagnetic spectrum that Herschel revealed, we share our experiences like never before. So here's what I'm thinking:

If you have a true prism at home with you, that's awesome. With a few other supplies and equipment, you can repeat the experiment conducted by Hershel to discover infrared light. However, you don’t need a true prism to get a sense of the rainbows inherent in sunlight or to see the sliver of the electromagnetic spectrum we call visible light. You can make a rainbow with the mist of a hose, a drinking glass filled with water, or even a CD (if you remember what those are). As long as the sun isn't too high in the sky, you can catch the sunlight at the right angle and create a rainbow and show it off. In fact, I want to see a rainbow of rainbows, folks, so get ʻgrammin. Take a moment today, with all this extra sunlight on our summer solstice, to find some rainbows and take a photo to share with the world. Pretty sappy, right? Well, I think I'll lean into it, so when you share your photo and tag it #sappyrainbowphoto on social media, along with #HaleakalaNationalPark, so we can all enjoy the rainbows out there. And just a heads up, we might share some of your photos on our Haleakalā NP pages for everyone else to enjoy.

If rainbows are corny or sappy or sentimental, so be it. The universe can be much worse things, and after enduring such long dark nights in the past I have no problem whatsoever taking a few minutes to let the sun shine, appreciating the simplest of wonders, and marveling at something as simple as split sunlight. [Music building, continuing under:] Today’s podcast was a production of Haleakalā National Park, written and narrated by myself, Laurel McKenzie. Special thanks to Rangers Kuaola Raymond, Sara Peyton, and Chris Petruccelli for helping me tell the Māui story. The podcast graphic was designed by Katie Matthew. A big mahalo, thank you, from me to all you listeners who tuned in on what was hopefully a sunny solstice day. For more information on Haleakalā National Park, the various resources we protect, and how to submit take and share your sappy rainbow picture, visit www.nps.gov/hale, or drop us an email at [e-mail]. Until next time, enjoy the new day, and happy rainbow hunting. Aloha. [Music fades out.]