SUN: ORIGIN, CHARACTERISTICS, STRUCTURE, COMPOSITION, ACTIVITY - ARTE - 2025

The Sun is the star that constitutes the center of the Solar System and the closest to the Earth, to which it provides energy in the form of light and heat, giving rise to the seasons, climate and ocean currents of the planet. In short, offering the primary conditions necessary for life.

The Sun is the most important celestial object for living beings. It is believed that it had its origin about 5 billion years ago, from an immense cloud of stellar matter: gas and dust. These materials began to stick together thanks to the force of gravity.

The Sun provides energy and heat to the planet, so that life can develop there. Source: Pexels

Most probably the remains of some supernovae were counted there, stars destroyed by a colossal cataclysm, which gave rise to a structure called proto-star.

The force of gravity caused more and more matter to accumulate, and with it the temperature of the protostar also increased to a critical point, around 1 million degrees Celsius. It was precisely there that the nuclear reactor that gave rise to a new stable star was ignited: the Sun.

In very general terms, the Sun can be considered a fairly typical star, although with mass, radius and some other properties outside of what could be considered the "average" among the stars. Later we will see in which category the Sun is among the stars that we know.

Humanity has always been fascinated by the Sun and has created many ways to study it. Basically the observation is done through telescopes, which were on Earth for a long time and are now also on satellites.

Numerous properties of the Sun are known through light, for example spectroscopy allows us to know its composition, thanks to the fact that each element leaves a distinctive trace. Meteorites are another great source of information, because they maintain the original composition of the protostellar cloud.

General characteristics

Here are some of the main characteristics of the Sun that have been observed from Earth:

-Its shape is practically spherical, it barely flattens slightly at the poles due to its rotation, and from Earth it is seen as a disk, hence it is sometimes called the solar disk.

-The most abundant elements are hydrogen and helium.

-Measured from Earth, the angular size of the Sun is approximately ½ degree.

-The radius of the Sun is approximately 700,000 km and is estimated from its angular size. The diameter therefore is about 1,400,000 km, approximately 109 times that of the Earth.

-The average distance between the Sun and the Earth is the Astronomical Unit of distance.

-As for its mass, it is obtained from the acceleration that the Earth acquires when it moves around the Sun and the solar radius: about 330,000 times greater than the Earth or 2 x 10 ³⁰ kg approximately.

-Experience cycles or periods of great activity, related to solar magnetism. Then, sunspots, flares or flares and eruptions of coronal mass appear.

-The density of the Sun is much lower than that of the Earth, as it is a gaseous entity.

-As for its luminosity, which is defined as the amount of energy radiated per unit of time -power-, it is equivalent to 4 x 10 ³³ ergs / s or more than 10 ²³ kilowatts. For comparison, an incandescent light bulb radiates less than 0.1 kilowatt.

-The effective temperature of the Sun is 6000 ºC. It is an average temperature, we will see later that the core and the corona are regions much hotter than that.

Classification of the Sun

The Sun is considered a yellow dwarf star. In this category are stars that have a mass between 0.8-1.2 times the mass of the Sun.

According to their luminosity, mass and temperature, stars have certain spectral characteristics. A diagram can be made by placing the star on a graph of temperature versus luminosity, known as a Hertzsprung-Russell diagram.

Classification of stars in the Hertzsprung-Russell diagram. The Sun is in the main sequence. Source: Wikimedia Commons.

In this diagram there is a region where most of the known stars are located: the main sequence.

There the stars spend almost their entire lives and according to the characteristics mentioned, they are assigned a spectral type denoted by a capital letter. Our Sun is in the category of star type G2.

Another fairly general way of classifying stars is into three large groups of stellar populations: I, II and III, a distinction made according to the amount of heavy elements in their composition.

For example, Population III stars are among the oldest, formed at the beginning of the Universe, shortly after the Big Bang. Helium and hydrogen predominate in them.

In contrast, populations I and II are younger, and contain more heavy elements, so it is believed that they have been formed with matter left by supernova explosions of other stars.

Among these, Population II is older and is made up of colder and less luminous stars. Our Sun has been classified within Population I, a relatively young star.

Structure

Layered structure of the Sun. Source: Wikimedia Commons.

To facilitate its study, the structure of the Sun is divided into 6 layers, distributed in well-differentiated regions, starting from the inside:

-The solar core

-Radiative zone

-Convective zone

-Photosphere

-Chromosphere

Core

Its size is about 1/5 of the solar radius. There the Sun produces the energy that it radiates, thanks to the high temperatures (15 million degrees Celsius) and prevailing pressures, which make it a fusion reactor.

The force of gravity acts as a stabilizer in this reactor, where reactions take place in which various chemical elements are produced. In the most elementary, hydrogen nuclei (protons) become helium nuclei (alpha particles), which are stable under the conditions that prevail inside the nucleus.

Then heavier elements are produced, such as carbon and oxygen. All these reactions release energy that travels through the interior of the Sun to spread throughout the Solar System, including Earth. It is estimated that every second, the Sun transforms 5 million tons of mass into pure energy.

Radiative zone

Energy from the core moves outward through a radiation mechanism, just as a fire in a bonfire heats the surroundings.

In this area, matter is in a plasma state, at a temperature not as high as in the nucleus, but it reaches about 5 million kelvin. The energy in the form of photons - the packets or "quanta" of light - are transmitted and reabsorbed many times by the particles that make up the plasma.

The process is slow, although on average it takes about a month for the photons from the nucleus to reach the surface, sometimes it can take up to a million years to continue traveling to the outer areas so that we can see it in the form of light.

Convective zone

Since the arrival of photons from the radiative zone is delayed, the temperature in this layer drops rapidly to 2 million kelvins. The transport of energy happens to be by convection, since the matter here is not so ionized.

The transport of energy by convection is produced by the movement of eddies of gases at different temperatures. Thus, the heated atoms rise towards the outermost layers of the Sun, carrying this energy with them, but in a non-homogeneous way.

Photosphere

This "sphere of light" is the apparent surface of our star, the one that we see from it (you must always use special filters to see the Sun directly). It is apparent because the Sun is not solid, but is made of plasma (a very hot, highly ionized gas), therefore it lacks a real surface.

The photosphere can be viewed through a telescope fitted with a filter. It looks like shiny granules on a slightly darker background, with the brightness diminishing slightly towards the edges. The granules are due to the convection currents we mentioned earlier.

The photosphere is transparent to some extent, but then the material becomes so dense that it is not possible to see through.

Chromosphere

It is the outermost layer of the photosphere, equivalent to the atmosphere and with a reddish luminosity, with a variable thickness between 8,000 and 13,000 and a temperature between 5,000 and 15,000 ºC. It becomes visible during a solar eclipse and it produces gigantic incandescent gas storms whose height reaches thousands of kilometers.

Crown

It is an irregularly shaped layer that extends over several solar radii and is visible to the naked eye. The density of this layer is lower than that of the rest, but it can reach temperatures of up to 2 million kelvin.

It is not yet clear why the temperature of this layer is so high, but in some way it is related to the intense magnetic fields that the Sun produces.

On the outside of the corona there is a large amount of dust concentrated in the equatorial plane of the sun, which diffuses the light from the photosphere, generating the so-called zodiacal light, a band of dim light that can be seen with the naked eye after sunset. sun, near the point on the horizon from which the ecliptic emerges.

There are also loops that go from the photosphere to the corona, formed of gas much colder than the rest: they are the solar prominences, visible during eclipses.

Heliosphere

A diffuse layer that extends beyond Pluto, in which the solar wind is produced and the Sun's magnetic field manifests.

Composition

Almost all the elements that we know from the Periodic Table are found in the Sun. Helium and hydrogen are the most abundant elements.

From the analysis of the solar spectrum, it is known that the chromosphere is composed of hydrogen, helium and calcium, while iron, nickel, calcium and argon have been found in the ionized state in the corona.

Of course, the Sun has changed its composition over time and will continue to do so as it uses up its supply of hydrogen and helium.

Solar activity

From our point of view, the Sun seems quite calm. But in reality it is a place full of activity, in which phenomena occur on an unimaginable scale. All the disturbances that occur continuously on the Sun are called solar activity.

Magnetism plays a very important role in this activity. Among the main phenomena that happen on the Sun are:

Solar prominences

Prominences, bumps, or filaments form in the crown and consist of high-temperature gas structures, reaching a great height.

They are seen at the edge of the solar disk in the form of elongated structures that interlock, being continuously modified by the Sun's magnetic field.

Coronal mass ejections

As its name implies, a large amount of matter is ejected at high speed by the Sun, at a rate of about 1000 km / s. It is because the magnetic field lines intertwine with each other and around a solar prominence, causing the material to escape.

They usually last for hours, until the magnetic field lines break apart. Coronal mass ejections create a large flow of particles that reaches Earth within a few days.

This flow of particles interacts with the Earth's magnetic field and manifests itself, among other things, as northern lights and southern lights.

Sunspots

They are regions of the photosphere where the magnetic field is very intense. They look like dark spots on the solar disk and are at a lower temperature than the rest. They generally appear in highly variable groups, whose periodicity is 11 years: the famous Solar Cycle.

The groups of spots are very dynamic, following the rotation movement of the Sun, with a larger spot that goes ahead and another that closes the group. Scientists have tried to predict the number of spots in each cycle, with relative success.

Flames

They occur when the Sun expels material from the chromosphere and the corona. They are seen as a flash of light that makes some regions of the Sun look brighter.

Death

Like any star, the Sun will disappear one day, but it will not be in the near future. Source: Pxhere.

As long as its nuclear fuel lasts, the Sun will continue to exist. Our star hardly meets the conditions to die in a great supernova-type catastrophe, because for that a star needs a much greater mass.

So chances are that as reserves are depleted, the Sun will swell and turn into a red giant, evaporating the Earth's oceans.

The layers of the Sun will spread around it, engulfing the planet and forming a nebula consisting of very bright gas, a sight that humanity could appreciate, if by then it has settled on a distant planet.

The remnant of the ancient Sun that will remain inside the nebula will be a very small white dwarf, about the size of Earth, but much denser. It will cool down very, very slowly, at this stage it may spend about 1 billion more years, until it becomes a black dwarf.

But at the moment there is no reason to worry. The Sun at this time is estimated to have lived less than half its life and it will be between 5000 and 7000 million years before the red giant stage begins.

References

1. All About Space. 2016.Tour of the Universe. Imagine Publishing.
2. How It Works. 2016. Book of Space. Imagine Publishing.
3. Oster, L. 1984. Modern Astronomy. Editorial Reverté.
4. Wikipedia. Hertzsprung-Russell diagram. Recovered from: es.wikipedia.org.
5. Wikipedia. Stellar population. Recovered from: es.wikipedia.org.