So you've come here to learn about the Sun...
Well, I can absolutely assure you that you've come to the right place!
This is a picture of the Sun taken by one of NASA's telescopes at the time of writing this!
The reality is that there's simply so much to say, so to give this article a bit more direction, I'm going to be talking you through the journey of a photon of light, right from the core where it's produced, all the way to your eyes!
I honestly believe this is the most interesting direction to take, while not sounding awfully that interesting to begin with, so bear with me, and I promise that you'll remember this for the rest of your life!
The beginning
The light that you see began its 93 million mile journey right at the centre of the Sun.
Here, temperatures exceed 20 million degrees Fahrenheit which combined with the resulting pressure of 20 thousand billion billion billion kgs of matter bearing down on the core, causes atoms to collide and fuse with one another in a process known as nuclear fusion.
The Sun is comprised of 99% hydrogen gas (well not strictly 'gas' but we'll leave it at that for now) and at the centre, atoms of hydrogen slam into each other at incredibly high speed.
This is no easy feat to achieve, as the protons that make up the hydrogen nucleus are positively charged, and getting two positively charged subatomic particles (essentially meaning the particles that make up atoms) to collide requires an immense amount of energy.
Recreating the type of conditions that atoms need to be under to fuse with one another would simply be impossible to do on Earth at the time of writing this - the "conditions" here being temperature and pressure.
Remember that the Sun's core is a highly pressurised, beyond scorchingly hot environment, and words simply cannot adequately describe a temperature of 22 million degrees Fahrenheit (I mean merely 100 degrees Fahrenheit is a very hot day on Earth, although I suppose it depends on the place!)
So protons of hydrogen are fused together, so what?
Well, when they combine, they form the next heavier element, helium, but in the process some mass is lost and is directly converted to energy - a photon of light. However, this photon of light is not what we see today, and in reality, undergoes a one million year journey from the centre of the Sun to your eye, and completely transforms in the process.
The direct conversion of mass into energy was first proposed by Einstein with mass-energy equivalence principle, which essentially states that there two manifestations of the same thing.
His famous equation E = mc² describes the equivalence of energy and mass mathematically, as a particles mass multiplied by the speed of light squared gives the rest energy of the particle.
Since the speed of light is 300 million m/s, the quanta of energy released from converting mass into energy is astronomical.
The start of a 1 million year journey to your eyes
This photon of light that's released from the fusion of two nuclei (or protons in the case of hydrogen, as the nucleus that makes up a hydrogen atom comprises only of a single proton), is highly energised, as we just discussed with the mass-energy equivalence.
In fact, if this photon were to come into contact with you, it would penetrate your body at an atomic level and split the atoms that make you up completely apart.... Sounds bad, right?
See, what we call "light" is essentially a form of radiation, or more specifically an electromagnetic wave within a specific range of frequencies and, simplistically put, radiation is merely a packet of energy that oscillates up and down throughout space-time, and how many times it completes these up and down cycles per second is what we call its frequency.
As a quick side note - Quantum Physics tells us that everything can be in fact be described by a wave function, contesting the previous concept that everything was made of particles. Electrons, protons, quarks... they can all be described as waves of energy in a quantum field.
It's the frequency of the particular radiation that differentiates it from other forms. See below an exhaustive list of the known radiation types, going from lowest frequency to highest:
Courtesy of NASA, again....
Looking at the middle of the spectrum, we can see "visible light" which is the range of frequencies that our eyes have been specifically adapted to, but it's important to remember that all radiation is essentially light.
What we describe as "light" is really "visible light".
So how does this relate to the photon of light that's emitted during nuclear fusion inside the Sun's core?
Well, remember how I mentioned that this photon of light was highly energised, and if absorbed by a human, would strip them down at an atomic level?
Gamma rays
Meet Gamma radiation, the electromagnetic waves with the highest frequency known.
Gamma rays are directly absorbed by the nuclei of the atoms that make up your body, since their extremely small wavelengths correspond to the minuscule distances between atoms, simply put.
When nucleons absorb energy, they become "excited".
Subatomic particles such as protons, neutrons and electrons don't like to be in these "excited" states, so their immediate response is to somehow lose energy so that they can return to their more stable states, which is exactly how light bulbs work, but that's a story for a different day.
You can check that one out here though if you're interested.
In the case of absorbing gamma radiation, the nucleons becomes excited and then immediately decay, releasing neutrons.
This process is known as photodisintegration. Therefore, at adequate intensities, gamma radiation would cause your atoms, and hence you, to rapidly decay into nothing....
This is what a gamma ray burst would like, in this case from a black hole! Credit to NASA yet again
So obviously we're not receiving this gamma radiation. We said that this is the photon of light that's released during nuclear fusion at the core of the Sun, but how and why does it change into the visible light that we can see today?
I mentioned that the journey of a photon is no simple one, and most certainly not a short one.
Photons of light can take a million years before they reach the surface of the Sun, and then it's only an 8 minute journey from the there to your eyes.
The speed of light
Let's just stop there and think about that - so the Sun is 92 million miles away, yet it only takes 8 minutes for the light to travel that distance?!
With just some simple maths, you can quickly determine how fast light really is...
8 minutes is 480 seconds...
And dividing the total distance by this time would give us the speed of those photons of light...
92 million/480 = 191,666 miles per second!
I've rounded the numbers here to make it look nicer, but the actual number is 186,000 miles per second (through an empty vacuum like space)
186 thousand miles every second....
That means that one photon of light could circumnavigate the entire Earth 7.5 times in just single...second...
But going back to the journey of a photon from the centre of the Sun, at this speed it should only take about 2 seconds to reach the surface , so what on Earth (or in the Sun should I say) is taking the photons the best part of a million years?
Let's talk about it....
The bulk of the journey
So we've discussed how at the core of the Sun, atoms are under so much pressure and heat that they collide together and fuse, generating the explosive power of millions of nuclear bombs every second, but what happens outside of the core?
The next "layer" of the Sun that proceeds the core is what we call the radiation zone.
The temperatures and pressures still remain extraordinarily high, but not quite high enough to fuse atoms together and what we have instead is a layer of plasma.
There are generally only 3 states of matter, or at least this is what you'll have been taught in school and while that is strictly true, there is an exception to this when conditions are extreme enough.
The radiation zone is essentially a soup of hydrogen atoms, heated to 12.5 million degrees Fahrenheit and compressed by a large proportion of the Sun's mass and, under such conditions, gases turn into plasma, but what exactly does this mean?
Earlier, we briefly mentioned a simplistic structure of an atom - a nucleus consisting of protons and neutrons surrounded by electrons that orbit in energy shells.
Note that this is indeed a very simplistic particle model of atoms, and we now believe that quarks (which make up neutrons and protons) and electrons are quantum "particles" that are better described as waves of energy that interact with matter in a particle like fashion.
They're excitations of energy in a quantum field.
Similar to how solids can melt and liquids can boil, gases can transform into plasma, and this happens in exactly the same way as the other two - when you heat them up high enough.
Although pressure can also affect states of matter, as we explore in this article.
At sufficient temperatures, electrons become adequately energised such that they overcome the electrostatic forces of attraction to the protons (since they're oppositely charged) and freely float around and in between nuclei.
This, is plasma.
But it takes a lot of energy for gases to turn into plasma, and hence plasma is practically non-existent on Earth, with only one exception...
Lightning.
Just before a lightning strike is about happen, gases are such an extreme voltage that they have enough potential energy to briefly turn into plasma.
Since the electrons in plasma are freely floating around, plasma conducts electricity very well which in turn allows for electrons to flow from the lower atmosphere to the ground, and visa versa.
If you're interested in learning more about how and why exactly lightning and thunder happen, then I'd recommend signing up as I have an article that's dedicated to that subject sitting in draft form, but I'll be posting it very soon!
As I'm sure you're all aware, lightning strikes are near enough instantaneous and they go as quick as they came, so the plasma will quickly radiate heat and drop back down to gaseous form.
When I say quickly, I mean the plasma will last for milliseconds, if that, but it's enough for scientists to determine more about this "4th" state of matter, particularly how the electrons become delocalised from their nuclei.
In contrast, the radiation zone (which is where the plasma lies, remember) will continue to be superheated by both the pressure of the gases that are being pulled toward it by gravity, and the immense quantities of radiation being released from nuclear fusion at the core.
Therefore, the plasma is there to stay.
So we've talked about what plasma is and how the radiation zone is full of the stuff, but what we haven't yet addressed is why this is a problem for our photons of light that have just left the core...
Electrons are negatively charged and we said that photons of light are gamma rays at this stage, which is a form of electromagnetic radiation - electromagnetic being the operative word here....
We know that charges interact with each other, particularly that opposite charges attract each other and same charges repel, but this isn't exactly what happens with electromagnetic radiation and electrons.
Yes, a photon is an oscillating packet of energy, but does it have a charge?
Well, the answer is no.
However, photons still interact with electrons in that when they are incident upon them (they come into contact with them), they are directly absorbed and the electrons enter an excited state.
But now we have another concept to think back to - remember how I mentioned that subatomic particles (so electrons, protons and neutrons - ignoring quarks for this subject) don't like being in these excited states?
Well, they don't.
The only way to exit an excited state is to lose enough energy to return to a lower energy shell and so the electrons do exactly that - they emit our photon of light, only a little bit of energy has been lost in doing so.
What does this mean for our photon?
It's still a gamma ray, but its frequency is slightly less than before, as it has lost a tiny amount of energy.
Since the energy of an electromagnetic wave is proportional to its frequency, then a decrease in energy will result in a decrease in frequency.
The radiation zone stretches over 200,000 miles.
That's 200,000 miles of delocalised electrons that will absorb our photon of light every time it's emitted by another, and that is exactly what transforms what should be a 2 second journey into potentially a 1 million year journey.
Every time a photon is emitted, it's projected into a random direction - could be up, down, left, right or somewhere in between. So its ability to progress up through the radiation zone is largely random.
However, despite meandering around in a zig-zag like pattern, there is a tendency to move toward regions of lower temperature and pressure which, in terms of the structure of the Sun, is outward in the direction of the surface.
Therefore, albeit after perhaps a million years, they eventually escape the radiation zone and enter the next, penultimate region - the Convection Zone.
Hitching a ride on Route 66 out of the Sun
Things get a lot more familiar here, I'm sure you'll be glad to hear.
At this distance from the core, temperatures have dived down to about 2 million degrees Fahrenheit (which is obviously still incredibly hot, but a lot cooler than 12 million degrees Fahrenheit), and most of the Sun's mass is below, hence the pressure has considerably dropped as well.
However, don't get carried away, as the convection zone is still an extremely violent environment, but serene enough to consist of very familiar chemistry and chemical processes, particularly in that heavier ions such as carbon and nitrogen can hold on to some of their electrons; at this point, nuclear fusion and plasma are both almost non-existent.
With that being said, the convection zone consists mostly of superheated hydrogen gas that moves from the bottom of the convection zone, all the way to the top in a circuit like routine, hence the name Convection zone.
You've probably heard of how heat rises, and it's no different in the Sun.
Gases naturally want to be in regions where there's less of them which, scientifically speaking, means that gases will move from regions of higher density to regions of lower density.
This fundamental process is known as diffusion and not only does it happen all around you, but it's also the very reason why many of the biological and chemical processes that you rely on exist.
For example, oxygen get's absorbed into your bloodstream in the lungs because the density of oxygen in your bloodstream (importantly the blood stream at the lungs) is lower than that outside of your bloodstream, so the oxygen diffuses into your bloodstream.
The exact same process happens with water.
Ever wandered why when you open the gap in the nozzle of your deodorant, the vapour is rapidly ejected out?
Because of diffusion.
The gases inside want to be on the outside, because the pressure is less, so as soon as you give them an exit route they rush out as quickly as they can.
Now here's another interesting one, and I really don't mean to make anyone sick of flying, although do I resent it myself? Absolutely.
Surely you've heard of how if you open the door mid-flight in an airplane, you and everything else will be sucked out at a million miles per hour (not really but you know what I mean)?
Well, that too is because of diffusion.
The higher you go, the less dense the atmosphere becomes, which is itself due to gravity being weaker the further from the Earth's centre of mass that you go (plus the fact that there's less atmosphere on top weighing down on particles beneath them), but because the pressure inside the plane has to be so high in order for you to be able to breathe and function properly, the difference in pressure between the inside and outside of the plane is significant.
Therefore, as soon as you allow air from the inside to go to the outside (remember atoms move from higher pressures to lower), then the gases inside the plane will rush out at an incredible speed, taking you and everything else with it.
That is at least until the pressure reaches an equilibrium, at which point you would no longer feel a force pushing you out, but you would fall unconscious pretty quickly due to insufficient oxygen levels.
Nearly there...
So that wasn't the most pleasant of details, but an important one none the less to understand; hydrogen gasses will move toward the surface, gradually becoming cooler as they do so.
But where does this leave us with our photon of light?
At this point, and after being ping-ponged around the radiation zone, gradually losing energy, our gamma ray has now been demoted to an x-ray (lower energy = lower frequency).
It's absorbed by the hydrogen nuclei present in the convection zone but this time isn't emitted and is instead retained by the nuclei.
This increase in energy from absorbing the x-ray, increases the temperature of the hydrogen gas which causes it to transpose toward the surface, a region of lower density - our photon essentially hicks a ride from the hydrogen gas!
After about a week of travelling through the convection zone, it finally reaches the very last region of the Sun.
The Photosphere.
Fortunately for us, as the nucleus that absorbed our photon gradually loses energy as it travels toward the surface, the amount of energy released when it's at the top is significantly less than the energy that it absorbed, and hence the frequency of the photon that's released is drastically less.
In fact, our gamma ray that turned into an x-ray has now degraded further into UV and visible light (amongst some other forms).
Just to slightly digress, let's talk about how sunspots, solar flares and solar wind form as technically they too can release photons that we can see.
The Sun has a magnetic field, just like the Earth.
In fact, whenever you see moving charges, you can expect to see a magnetic field.
The problem is that the Sun rotates much quicker at the equator than it does at the poles, which causes the magnetic field to tangle up, creating a magnetic mayhem of charges and when they do so, they stop the flow of rising gases, creating regions of lower temperatures called sunspots.
Sunspots can be very clearly made out with just a standard refractor, (although make sure you use a sun filter to avoid irreparable damage to your eyes!), as with the convection currents paused, no photons can escape, and hence they appear as dark patches on the surface of the Sun.
When magnetic field lines tangle up, they can cause explosive jets or bands of charged ions to be dispersed from the surface, but when they combine with one another, they release huge amounts of "pent up" energy that causes charged ions, protons and electrons to be ejected into space at over 4.5 million mph!
Such events have been coined solar flares, and the explosive force produced from them are of the magnitude of millions of nuclear weapons.
Solar wind is enough phenomena that arises from the outward expansion of plasma from the surface of the Sun and contains energetic charged particles, such as electrons, ions, protons and alpha particles that travel at fractions of the speed of light.
Fortunately for us, these charged particles interact with the Earth's powerful magnetic field which, in summary, redirects them to fly over the poles,.
Interestingly, this is the very reason for the northern/southern lights.
If you're interested in the specifics of that, then I'd highly recommend you to check out this post: Click here!
See below a solar flare.... Credit: NASA
And here's a picture of the Sun with visible sunspots.. Credit: NASA.
So now our photon has finally left the grasp of the Sun.
With photons of light being emitted in 360 degrees, the likelihood is that the majority of photons will now head for a journey lasting thousands if not millions or billions of years.
From here, it's an:
8 minute journey to Earth,
80 minutes to Saturn,
4 hours to Neptune,
16 hours to the edge of the solar system,
4 years to the nearest start system (the alpha Centauri system),
1500 years to the Horsehead nebula,
2.5 million years to the nearest galaxy (Andromeda) and;
33 billion years to the furthest known galaxy (as of 2023 - HD1).
33 billion years for a photon travelling so fast that it could circumnavigate the Earth 7.5 times in 1 second.
That is the true scale of our universe and it only seems to be getting bigger as technology advances and allows us to see further, both in space and hence back in time....
For the light that we can see, those photons started their journey hundreds of thousands of years ago and finished their journey becoming a very part of you.
Every second of every day, trillions of photons are absorbed by the Earth, enough to power human civilisation for 27 years!
Remember - every decision that you make, you can do so because of the Sun.
Conclusion
And that concludes the journey of a photon of light, right from its humble beginnings at the core of the Sun.
Suffice to say that there's truly at least one lesson to be learned from this article:
The light that you see today began its journey long before your ancestors had even left the plains of Africa.
Remember that the next time you choose to make a decision in your life - is this a good use of the Sun's energy?
Never forget that the Sun is losing energy to provide you with it.
But where does the Sun get its energy from, Ryu?