PHY: THE SUN
Hello everyone, David here, and today we are going to talk about a big ball of flaming gas that quite literally powers up life down here on Earth, and we call it The Sun. It is a crucial element of every being on our planet, so let’s take a closer look at it, shall we?
First off, before we get into any detail, we should investigate the Sun’s structure.
In this image, you can see the 6 layers that compose our star. The other three things are not layers, but rather phenomena or characteristics of one or more layers, and we will take a look at them later. Let’s then take a closer inspection of each one of these sections.
1) Core
The Sun’s core is where the magic happens. It is where the star’s energy comes from, fruit of a very interesting and powerful event called Thermonuclear Reactions.
Ever wondered where did all this heat come from? Well, here’s the answer: Hydrogen! Well, more like Hydrogen when put under 250 billion atmospheres of pressure, such as is the Sun’s core. These values are tremendously high and would obviously kill any of us in millionths of seconds, but are what originates heat in there. You see, all these Hydrogen atoms are forced together in the core, and when two of these bond together, they form Helium and insane amounts of energy, the latter of which is partially expelled in the form of heat.
The diagram above shows the exact steps of this reaction. The “positron” particles are what we call antimatter, and are basically the electron’s twin brother but with an opposite sign, i.e, positive. I don’t want to get much into this as it would shift the focus from this article, but we could definitely talk about that later!
The very same thing that gives life to a star kills it later on: it is estimated that when Helium eventually accumulates to a concentration of about 12%, the core will shrink, causing fusion to accelerate, making the Sun grow larger and larger, consuming Mercury, Venus and maybe even Earth on a stage called Red Giant, it collapses into its own nucleus, becoming a White Dwarf with a beautiful Planetary Nebula around it.
2) Radiative Zone
The Radiative Zone, as the name rings, refers to radiation, and it is in this area that energy flows in the form of radiation through photons and thermal conduction, not convection as is the case for the next layer, whose name kinda gives it away (Convective Zone). This is also the biggest layer of the Sun, and it is the region in which the temperature really drops: from 15 million K near the core to about 1.5 million K when we reach the
Convective layer. This happens because this is also an incredibly dense area, so when a photon leaves the core, it can’t travel too far before it hits or is hit by another particle, making it gradually lose energy and wavelength. It also takes a tow on its speed: a gamma-ray takes approximately 171 thousand years to leave the core and reach the Photosphere, which is… quite a lot of time.
3) Convective Zone
The Convective Zone is the place where energy flows through convection, i.e, a cycle of heating-cooling in a system. Let’s take a look at a more relatable example to understand convection better, an air conditioner, for example: why is it placed up high near the ceiling and not down low, near the floor? Well, when we place such machine up high, when cold air leaves it automatically goes down (because cold air is denser). When it eventually arrives on the floor, it warms up as it gets in contact with the already hot air there, which makes it go up, and so on and so forth. Because we create this cycle, cold air will flow through the whole room. This cycle is called a Convection Current, and is precisely what happens on the
Convective Zone, only there’s no such thing as “cold and hot air”, but rather unimaginably-hot and a-little-bit-less-unimaginably-hot plasma.
These Convection Currents are visible from the Photosphere, and we will take a look into that more closely right now.
4) Photosphere
The Photosphere receives its name as it is the layer that we see when we look up, despite there being another one theoretically “covering” it, from which light is radiated. This area is also the place where two interesting phenomena occur, these being Granules and Sunspots.
Granules are caused by the Convection Currents of plasma we talked about earlier. When that hot gas reaches the top and cools down, it starts its way back to the bottom, and the area in which it makes this “turn” - i.e, reaching the top and going back down - is where we see the granulations. These areas are slightly darker and colder Similarly, whenever we boil water we can see a little “wavy thing” going on in the pan, which is a smaller case of granulation, only in your water, which is arguably cooler than the Sun.
There are also other cooler areas of the Sun that show up eventually and leave after a while. The so-called Sunspots are darker areas constituted of two regions: Umbra, the innermost region, reaching temperatures of about 3800K, and the Penumbra, the outermost region, slightly hotter than that. They are believed to be caused by the Sun’s magnetic field, which inhibits the Convection Currents, forming these colder - therefore darker - regions. An interesting aspect of Sunspots is that they appear to follow a cycle of roughly 11 years - the same as the Solar Cycle, which is not a coincidence.
5) Chromosphere
The Chromosphere, just above the Photosphere, is a very dim, low-density layer compared to the one below, visible only during solar eclipses or with special spectroscopy equipment, due to its contrast to the Photosphere. It is there that we can observe filaments, which sometimes form arcs called prominences, that are small ejections of mass. Sometimes these prominences are followed by larger solar activities, such as solar storms or coronal mass ejections, which we will discuss in a bit.
6) Corona
No, not the Coronavirus, although they both originate from the same latin word: Crown. The Solar Corona resembles, in fact, a crown, and goes all around the Sun. It is the outermost layer, invisible with the naked eye, and the one that could originate a lot of trouble for us if some special conditions are met.
Sometimes an event called Coronal Mass Ejection (CME) occurs, and the name is pretty self-explanatory: the Corona ejects a lot of its mass in the form of ionized gas. This is similar to events called Solar Winds and Flares, as they are all ejections of mass in the form of ionized gas, but they all occur in different scales, i.e, ones are bigger and more intense than the others and can happen independently, besides some other differences (Solar Winds, for instance, are continuous, always happening). CME’s plow right through Solar Winds, for example, as they are way stronger and can cause bigger damage when hitting Earth.
Solar Winds are a topic of interest, as they are the cause of the Auroras! When these ionized gases hit Earth, they are captured by what is called a Van Allen Belt, and carried slowly to the poles by our magnetic field, creating those beautiful “sky waves” of green flows due to the ionized gases messing with the atmosphere, that we call Auroras or Northern Lights. They can also be seen from the Space Station, and you know that anything from space looks twice as beautiful!
Well everyone, that’s about it for today’s post! I didn’t talk much about how The Sun was born or how exactly will it die, and that’s because for the next posts I will do a mini-series talking only about stars! It should be fun, so stay tuned for that. Also, make sure to check out our youtube channel that we created! We will be posting some videos about our topics, so there’s that. Click here to watch our first introduction video!
Alright everyone, I hope you enjoyed today’s post and I’ll see ya again in the next one! Stay safe! Peace!
tá ent o sol n tem corona mas ele meioq eh corona