Episode of Uncertainty Principle about our host star: the sun.
One of the films on my list of science fiction movie masterpieces is the sci-fi thriller Sunshine. I would very much recommend it, but I’m not here to plug the movie. The movie takes place in a future where the lifeblood of our solar system, the sun, is dying, and a mission is sent to restart it. The sun is central to the plot, and the movie is filled with elements related to it. Not least of which is the name of the ship: Icarus.
The story of Icarus is a common Greek Myth that many of you may know: Icarus flies on wings made of wax and feathers, but he soars too close to the sun, his wings melt, and he falls to his death. Like most Greek stories, it’s purpose is not literal, but allegorical. Today we still use phrases like “flying too close to the sun” to describe over-ambition. There is a similar Chinese myth about ambition in which a giant chases the sun, and dies after getting too close. Clearly the purpose of these stories is their morals, but they raise an interesting question: how does temperature change the closer you get to the sun? Was it the thought of the Greeks and Chinese that the closer you were to the sun, the warmer it got? It would have been a fair assumption to make. The sun was obviously a source of heat, and other sources of heat, such as fire, radiate more heat to areas closer to them. But anyone who’s climbed a mountain could tell you that this is not so – at the altitude of mountain tops, it is consistently colder.
To answer our initial question, yes, things do get warmer the closer you get to the sun, but the sun is so distant that a few thousand feet closer or further ultimately doesn’t make much of a difference…in space. But we’re on Earth, where there is a difference with altitude, and not a consistently colder or warmer difference either. In this sense, the sun and the atmosphere are closely linked to maintaining the earth’s temperature. Take the moon for example. The moon is at about same distance from the sun that we are, on average, depending on it’s orbit around us. The moon also has virtually no atmosphere in comparison to earth – a hundred trillionth of the atmospheric pressure we have. The earth’s atmosphere not only keeps us warm, but also keeps us cool, and keeps our temperature steady. Granted, there are other factors, such as the length of the lunar day which is nearly a month long, but the moon’s temperatures vary from 253 degrees F (123 degrees C) during the day, and -387 degrees F (-233 degrees C) at night. Earth, obviously, has more mild temperatures, and it is very well thanks to our atmosphere.
Our atmosphere does more than just let us breathe – in fact, it has quite a few jobs, as well as many layers. The atmosphere has what is called a lapse rate: a change in temperature at different elevations, or layers. It’s hard to tell exactly where layers begin and end, so the elevations of the layers will be approximate.
The troposphere is the part of the atmosphere you live in, and begins at sea level. This is where all the weather happens, and the temperatures are fairly mild, steadily decreasing the higher up you get into the troposphere. Above the troposphere is the stratosphere, beginning at around ten to twenty kilometers above the earth’s surface. This is where airplanes fly, and where the ozone layer is located. Ozone protects us from the harmful ultraviolet radiation from the sun, so its disappearance is not ideal. Throughout the stratosphere, temperatures start to rise again, but not by much. Starting at about 50 kilometers is the mesosphere, the part of the atmosphere where meteors burn up and become “shooting stars”. Like the troposphere, things get increasingly colder as you go up the mesosphere, all the way down to -90 degrees C at the top, the coldest part of our atmosphere. At around 90 km we reach the thermosphere, which as the name suggests, is very very hot. The thermosphere absorbs lots of x-rays and ultraviolet rays, raising temperatures to anywhere from 500 to 2000 degrees celsius.
Now this is where things get kind of weird. Above the thermosphere is the exosphere, about the place where “outer space” begins. There seems to be a disagreement within the scientific community about whether or not the exosphere is actually part of earth’s atmosphere or just a part of space. Regardless, the exosphere is very very thin, it might as well be a vacuum to us. But what’s the weather like up here? It’s technically very very hot, but only technically. On earth, we measure temperature by the amount of energy being bounced around within the immediate atmosphere. The atoms and molecules of the atmosphere are vibrating in an active gaseous state, and are close enough to exchange energy with one another. At the exosphere, atoms and molecules are in an excited state to be considered very hot, but they barely ever make contact with one another to exchange energy. You would feel a different kind of temperature. It would be sort of like being on the surface of the moon. Up here, it is very hot in direct sunlight, but becomes very cold once you get into any kind of shade. Temperature is directly affected by whether or not you are in sunlight. Let’s bring the exosphere down to our level. Are you inside? You’ve immediately frozen to death. Now let’s go outside into the sun – you’re burnt alive. It’s a very hostile environment to life.
Let’s leave earth, and travel to the two planets closer to the sun than us, being Mercury, and Venus, Mercury being the closer of the two. Ultimately, things get hotter the closer you get to the sun, as you receive more solar radiation. But there’s a problem: though Mercury is closer to the sun than Venus, it is not the hotter of the two. Mercury, like our moon, has a virtual vacuum of an atmosphere. It’s surface temperatures vary from -220 degrees C to 420 degrees C. In contrast, the Venus surface temperature lies at over 460 degrees C. This is caused by its thick and carbon dioxide heavy atmosphere, which creates a tremendous greenhouse effect – a hint at what excess carbon dioxide can do to climate. But if these two planets had similar atmospheres, Mercury would likely be the warmer of the two.
Which brings us to the heart of our solar system, Helios itself. Helios is the name the ancient Greeks gave to their sun god. Perhaps if they knew what we do about the sun, they would revere it all the more. Even still we bow our heads in its blinding light. Now of course I’m not calling for the worship of our sun as a deity, but if you ever need to reference a higher power, the sun is a prime example. And as I will show, it is definitely worthy of our respect, even though it is a small, ordinary star, in our galaxy.
The sun is a phoenix. A much larger star in eons past held the material that would one day become the sun, and us. In a cataclysmic death that we don’t quite understand called a supernova, this star would have flung it’s contents across space creating a massive cloud of stellar gas and dust. It is from this dust that the sun, and its siblings, would be born. This gas and dust, mostly hydrogen and helium, would gravitationally collapse, and once the gravity became strong enough, the pressure of the star would cause fusion to occur, and a star comes to be. Similar stars – perhaps thousands more – would form in the same gas cloud, and over the millions of millennia, they would drift throughout the galaxy, never to meet again. The well known star cluster Pleiades is a prime example of this. These stars were born in the same stellar nursery, but they have not yet drifted apart. It was not until May of 2014 that the announcement of a likely sister of the sun was found. The star’s name is HD 162826, and is 110 light years distant. It is in the constellation Hercules, and is not visible to the naked eye. Siblings of the sun could aid in the search for extraterrestrial life, because of the similar chemical makeup of our solar systems, assuming they have planets.
It was over four and a half billion years ago that the sun began its monarchy over the solar system. It contains 99.86 percent of the solar system’s mass; the other 0.14 percent is the rest of the solar system, the moons, planets, and us. We are the debris of the sun’s formation. Weighing in at approximately 2×1030 kilograms, the sun is over 300,000 times the mass of the earth. In shear size, the sun is like a million earths compacted together. With a core burning at 15 million degrees celsius, the sun is a great fusion reactor that burns with a fire that would put Hell to shame. It is a source of power unlike anything we could conceive. Through it’s immense heat and density, it fuses Hydrogen together to form Helium (which get’s its from the sun god Helios). When this happens, light particles, or photons, are released, and over the course of tens to hundreds of thousands of years crawl their way to the surface, and to us. The sun releases the equivalent of 90 billion megatons of TNT per second. For perspective, the energy in one megaton of TNT could power the average american household for over a hundred thousand years. Ninety Billion times that. Every single second. In the face of that, our reluctance to convert to solar energy seems, inexcusable. There are hypotheses about hyper advanced civilizations that encompass stars in “dyson spheres” – massive super structures built to capture a great deal of the energy leaving a star. Surely our primitive civilization can spare a few solar panels per household. Searching for stars that don’t emit visible light could also aid in the search for extraterrestrial intelligence by hinting at dyson spheres. Will we ever have the ingenuity to harness such energy?
We owe our existence to the sun. The vast majority of surface life on planet earth evolved because the sun was there to provide just the right amount of energy. And just our luck we have a particularly stable star as well. If the earth is our mother, then the sun is our father. The sun inseminated the earth with the necessary tools to create life. But some of the resources came from elsewhere. The sun converts hydrogen into helium through fusion. In the early universe there was only hydrogen and maybe some helium. So where do we, other carbon based life-forms and rocky planets come from? The stellar ancestors of our sun that we mentioned earlier are the source of such elements. Much larger stars can convert light elements like hydrogen and helium into successively heavier elements. Such stars burn through their hydrogen faster, and in their explosive deaths, they shoot their elements out into space. There were no planets orbiting the first generation of stars, because such elements had not been formed, so we can thank stellar fusion for our existence.
A different death awaits our sun. As the sun runs out of hydrogen, it will grow into a red giant, engulfing the inner solar system – meaning us. This will happen in five billion years time, which to the sun is twenty turns around the galaxy. So our sun is middle aged. Hopefully, the descendants of humanity will have moved on by then.
In it’s power, and longevity, dare I say the sun is godlike, but unlike a deity, the sun does not make choices about our existence, and cannot be appeased. In July, 2012, a massive solar storm missed earth by about a week. It was one of the strongest in recorded history. Human beings themselves would have been unscathed, but as a technology dependent civilization, the impact on our infrastructure would have been great, effecting things like the internet and gps for quite some time. Recovering from such a disaster completely would take quite some time. Perhaps we should consider sun proofing our technology.
Solar storms can be stronger. In his book A Short History of Nearly Everything, Bill Bryson notes that some of the mass extinctions on planet earth remain without explanation. A possible hypothesis is super strong solar storms that could wipe out much of life itself. And more eerily, would leave not a single trace in the fossil record. My intention is not to frighten you, we’ve been around this long without such an incident, but there are dangers out there in the universe, and they are numerous. And as an intelligent civilization, we can prepare ourselves for such catastrophes.
When it’s a particularly sunny day, I encourage you to go out and enjoy the sunlight, and the uncontainable power that lies behind it. It brought you here.
Thanks for listening, and keep exploring.