Some details about the Sun

One of the stars in our Galaxy.

Voir la version Haitienne de ce texte: https://haitiastronomie.blogspot.com/2023/05/kek-detay-sou-soley-la.html

The sun is a star, a large ball of gas that holds its body thanks to the force of gravity, and also thanks to the power that comes from the nuclear fusion reaction that takes place inside it. To study the Sun, astronomers divide it into different layers that have to do with how the structure is for each depth level.

And well, today, we will see, together with Captain Astro, what the Sun is in detail...

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I was telling you that to study the Sun, astronomers divide it into different layers that have to do with how the structure is for each level of depth. And well, so, on the outside, say the skin of the Sun, this part is called the photosphere; this is where, on the surface of the Sun you can see visible light coming out. It is not thicker than 500 km, while the entire Sun has a radius of 700,000 km.

Below the photosphere, there are other regions such as the convection zone that measures 200,000 km as a radius, and the radiation zone that has 300,000 km, and finally the inner Sun that measures 200,000 km; Stack upon stack, all these layers make the Sun measure, as we said, 700,000 km as a radius.

So, the Sun is a ball with a diameter of almost 1.5 million km. It is much larger than the Earth, which measures only 12,742 km, and concentrates 99% of all matter in the solar system, because it has more mass than all the planets and everything else that makes up the solar system.

Attention, we are talking about the solar system, not the Galaxy, nor the Universe: these things are much bigger than the solar system, and in the past astronomers confused them between the solar system and the universe.

Deep inside the Sun, which astronomers also call the core, the nuclear energy is made to be sent after to the region above it, the radiation zone; it is in the radiation zone that the energy crosses in the form of rays to reach another higher region called the convective zone. Right there, in this convective zone, a lot of matter will be stirred when the radiation energy reaches them. It will make a series of movements from down to up, and then from up to go down, like “bouillie” in a pot on fire. In physics, the phenomenon where hot matter rises while the less hot matter descends, scientists call it convection. Therefore, the region that stirs above the radiation zone, astronomers call it the convective zone.

Don't forget, it is 200,000 km deep, and the mixing that takes place in it is divided into small areas called cells, from the bottom to the top of the entire convective zone. The lowermost cells are larger, warmer than those above.

So a bunch of small convection cells will appear all below the layer covering the convective zone. As the upper layer is transparent relatively to this area, astronomers can observe these last groups of cells. To me, they look like when you look at a pot of ground corn boiling over a stove: you see little places rising up and breaking apart and bursting out. Well... it's a little personal comparison... I hope you understand the idea I want to pass...

Pay attention to listen well... The amount of solar energy that reaches the surface of the Earth's atmosphere, especially the uppermost part of the atmosphere, when scientists conventionally quantify it for 1 m^2, is called the solar constant. The total amount of energy the Sun provides for 1 second is called solar luminosity. It is an amount of energy that you could calculate if you took what we called the solar constant, and you would multiply it by a sphere that would wrap the entire Sun while it was touching the Earth's atmosphere. This imaginary sphere would have a radius of 1 AU, the distance between the Earth and the Sun, 150 million km.

Much of what we know about what the inside of the Sun is like, is thanks to a series of mathematical models...because, as you know, we cannot go inside the Sun's belly to experiment.

So, one of the models astronomers have finally developed, which corresponds well with the properties they have observed, is called the "standard solar model".

In addition, they also managed to study how the surface of the Sun behaves with a series of vibrations, like … say, a tremor of its surface; therefore, astronomers also call this type of study helioseismology... well, a word that would be similar to the study of earthquakes on our planet...

In the Sun, it is a series of pressure waves that come from the inner core and will act on the surface and these tremors, and the astronomers will use them to better understand what is happening inside the core, in the structures that are below, which cannot be analyzed directly.

Therefore, mathematical modeling and helioseismology are two very important tools that allow astronomers to better understand what is happening inside our star.

Do you remember I was talking about an area inside the Sun called the convection zone where a lot of gas is stirred up according to the temperature level?! That's how they formed a series of cells from the bottom to the top...remember!? Well, the higher cells form a series of small seeds...I also remember, we compared this to a boiling pot of food...well...What I want to talk about here is that... , in addition to the small granulations that appear on the surface, there is a series of larger and lower granulations, they will try to climb up to exit through the photosphere.

Don't forget, the photosphere is the part of the Sun's body that is used as skin or direct cover. It is transparent compared to the lower layers, so astronomers can observe the small granules, and even some large granules that come from below and these are also called supergranulations.

Don't forget, the Sun is a ball of gas, and the part we just talked about is the area of gas that keeps its body firm under the pressure of gravity, from the core to the photosphere.

But our star, like all stars of course, is producing a lot of energy in the form of electro-magnetic. It is the interaction between this outgoing energy and the pressure of gravity that keeps the Sun alive for so long.

Well, let's leave the body of the Sun to enter the gas that surrounds the Sun, so the gas that constitutes the energy coming out. Astronomers also categorize it into layers, based on its distance from the photosphere. This is how we begin to find the chromosphere, the lowest part of the Sun's atmosphere. When astronomers analyze this part thanks to a tool called a spectroscope, it gives most of the number of spectral lines that are seen. In another episode we will talk in more detail about the tool called the spectroscope. Above the chromosphere, there is another region that astronomers call the "transition zone". Here, the temperature rises, from a few thousand degrees kelvin to millions of degrees kelvin.

Above this transition zone, you will find the solar corona, the highest and hottest area of the Sun's atmosphere. They also call it the corona, well... it's not the virus, please!

The gas in the corona becomes so hot that, when it begins to reach a distance that is estimated to be 7.5 times the diameter of the Sun, it reaches the speed that allows it to escape, withdrawing completely from the Sun's gravity; And so the solar wind begins to take shape itself and go far in the solar system.

On the body of the Sun, there is a series of small dark marks that an astronomer can observe. They have been observing this for a long time, since the telescope became common as an astronomical tool. I will never forget to remind you to never look at the Sun with a telescope that is not specially designed for this...you can burn your eyes! You have been warned!!

Well, let's get back about these dark spots on the Sun. Astronomers simply call them "sunspots." "sunspot" in English. It is a series of areas on the surface of our star that may have the size of Earth; They are less hot than the surrounding areas on the surface of the Sun, and there is a lot of intense magnetic activity where they are. The number and location of their appearance on the surface varies over a period of 11 years. Astronomers call these types of variations "sunspot cycles", because the solar magnetic field goes up and down like this every 11 years. The direction of the magnetic field changes completely, from one sunspot cycle to another sunspot cycle, so every 11 years.

This is what will explain it takes 22 years for a magnetic field to return to its place completely, which is what astronomers call the "solar cycle".

Be careful not to confuse these 2 basic notions to better understand the Sun: "sunspot cycle" vs "solar cycle". While the first (sun spot cycle), is related to the change in direction of the magnetic field, the second, (solar cycle), is related to the complete return of the magnetic field as it was originally.

The activity of the Sun, namely the movement of the Sun on its surface, appears to be more related to a series of sunspots that are grouped together. Astronomers call these areas "active regions" where there are "prominences", "flares", and "coronal mass ejections". Prominence is when a strong magnetic activity rips off matter on the surface of the Sun and throws it out. The explosion, which is called "flare" in English, is an explosion that occurs in an area on the surface of the Sun, it is violent and sends particles and radiation to the interplanetary regions. Well, the biggest of activity on the surface of the Sun is the "coronal mass ejection"; it is a large amount of matter that the magnetic field tears off the surface to send it into space. It's huge...it's bigger than a planet. And it can cause a lot of problems if it happens in the direction of the Earth, because when these particles are torn from the Sun, they travel far in the solar system. Many dangers for spacecraft and astronauts who would have the misfortune to cross it on its way to space. And if it were to reach Earth, there will be a lot of damage to electronic equipment and electrical networks. This has happened a few times already...

The Earth has a magnetic field and a special radiation belt called the Van Allen Belt that can help protect our planet from solar particles...but when many are arriving after a major solar activity, something happens high in the atmosphere in the north pole or south pole area. This creates a series of special lights called aurora borealis or aurora australis. They are not dangerous because the particles remain completely in the atmosphere. But if one day, may God protect us, during a great solar activity, the Earth would be in an area where it would receive a lot of particles, great damage could be done.

Well, where does the Sun get all that energy? It is because of nuclear fusion reaction process between the nuclei of hydrogen atoms. It is one of the 4 fundamental forces of the Universe that makes 2 hydrogen nuclei meet to become helium, and this reaction gives a lot of energy. As the Sun has a lot of hydrogen, and thanks to the high pressure of gravity of this mass of hydrogen on the core of the Sun, all the conditions are met for this reaction to take place. It is the reaction that specialists call "proton-proton chain". In general, some mass is lost in this reaction, but in return, energy is produced. There is a rule in physics called the law of conservation of mass and energy that allows us to understand this phenomenon where we will end up with the production of light that also reaches us on Earth.

In addition to energy and helium, this nuclear reaction also produces positrons, which are antimatter, and neutrinos. The neutrino is a particle with a very very small mass. So it does not interact much with the matter that surrounds it, and this will allow it to quickly escape from the Sun. This behavior will give astronomers many problems to measure and control this particle when it leaves the Sun. Finally, they will understand the behavior of the neutrino, when they will understand that this particle, from the moment it comes out of the Sun, before it even reaches the Earth, it has already changed, it has oscillated, as the astronomers used to say!.

Thanks to telescopes equipped for this, and other tools such as spectroscopes, astronomers have come to know a lot about the Sun, and this allows them to make many theories about the stars in general. Other stars are far, far away, but our Sun is only 150 million km.

Likewise, there are many other things that we do not yet know completely about the Sun...we are still doing research, and there are a series of observatories put in space by major space agencies to gather valuable data for us, which makes science advance. We also know that they did not send space missions directly to the Sun, because the heat and many radiations of our star would make these missions very difficult. However, there have been many space missions that have reached a certain distance to study the Sun and its surroundings.

Here are some of them:

Solar Maximum Mission launched in 1980, Solar and Heliospheric Observatory (SOHO) launched in 1995, Solar Dynamics Observatory (SDO) launched in 2010 and Parker Solar Probe launched in 2018.

The Agence Spatiale Européenne (ESA) has sent space missions to study the Sun, such as Ulysses launched in 1990 and Solar Orbiter launched in 2020.

Japan launched the Hinode mission in 2006.

These missions have provided a lot of information about the Sun and how it works, including many details about solar flares and solar storms, and details about their actions on Earth and the space environment.

Finally, as we know, without the energy provided by the Sun, life would be impossible on Earth. The sun is not here indefinitely, it is true, it has to exhaust all its hydrogen stocks in nuclear reactions. It will function again for another 5 billion years. But if it wasn't there, there wouldn't be a solar system, the planets wouldn't be there, and there wouldn't be a habitable zone in the system so we would not be here to explain that to you.

Enjoy the Sun while you're here, while it's here too.

Thank you for watching this episode. Don't forget to like and subscribe to the Société Haitienne d'Astronomie channel and share it with people you know who are interested in astronomy in their native language. I am Captain Astro and I am waiting for comments and questions on social media or email or phone/WhastApp at +50938407775.

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Production: Société Haitienne d'Astronomie