When we look at the sun, what we can see is a vibrant yellow-colored disk that glows and makes our days bright. Apart from these pieces of information, our eyes can’t help us. But, the sun is not that simple!
The unaided human eye has limitations to explore the real nature of this massive object that dominates the entire solar system.
Even if, our eyes face restrictions, the human brain, and its imaginations are more powerful. The man-made technologies and his ideas thus opened up the whole life of the sun to us. Let’s have a voyage through those obtained information.
Table of Contents
Formation of the Sun
The Sun, which is a sphere of hot plasma, does not appear in the sky magically on one morning. The formation of the sun was a long and tremendous process.
When one speaks about space, it symbolizes an empty condition where we cannot trace even the presence of matter. But, Space is filled with gas and dust. This interstellar gas and dust formed an enormous rotating cloud called the solar nebula.
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This nebula in its slow rotation gradually pulled together by its own gravitational force. Thus increased gravity collapsed the nebula, which then spins faster and gets flattened into a disk.
This caused the whole mass to concentrate on the center. Sun which is the brightest star thus accounts for nearly 99.8% mass of the entire solar system. The process which we discussed now is commonly known as Nebular Hypothesis or Solar Nebular Theory.
Other Theories
No one has ever witnessed these evolutions, so there exist other theories too, which explain the formation of sun and the solar system on the basis of different characteristics and observations.
Some of them are accretion theory, proto planet theory, capture theory, modern laplacian theory and so on. But, the mostly widely accepted theory which explains the formation of sun, without doubt, is Solar Nebular Theory.
Composition of the Sun
Our home star is a giant ball of gases. These gases are present in the earth’s atmosphere too. Then, what made the sun’s nature so distinct from the earth.
The varied proportion of these elements is the key. 70% of sun is filled with hydrogen, 28% of helium and the remaining small quantity is the combination of carbon dioxide, oxygen and nitrogen.
In terms of atoms, 91% is made of hydrogen while 8.9% by helium. Temperature of sun’s surface is about 5726 degree Celsius.
Also, another point to note is that sun is not a solid structure and not even liquid, it exist in plasma state where matter are made up of superheated gas, possessing charge.
Zones the Sun (Interior)
Interior of the sun is divided into three zones, the core, the radioactive and the convective zone. Core is the innermost layer and the hottest area (27 million degree Celsius) and is made up of dense plasma.
Fusion reaction which fuels the life giving star took place in this part of the sun called core and release vast amount of energy.
The main contribution of the heat, produced by the sun is by this inner core of the sun. Even core is made up of plasma, it moves smoothly like a gas. The high amount of produced energy move from the innermost core towards the outer layer.
Radiative zone
The layer outside the core is known as radiative zone. The energy which is released by the core travels through this zone in a very slow pace.
The layer is characterized by the method of energy transfer, which is through radiation and hence the wording radiative zone. The particle which travels through this zone is called photons, which are particles of light. These photos carry the produced energy from the core.
A single photon move a few millimeters to collide with another particle, thereby transferring its energy. Even when photons can travel at the speed of light, continuous bouncing causes immense delay.
For a single proton it may take million of years to travel the entire radiative zone. The process continues to handover the energy to next outer layer of the sun.
Convection zone
The layer which surrounds radiative zone is called convection zone and is the outermost layer. This layer is comparatively ‘cooler’ than other layers; hence it is opaque and creates a challenging path for the radiation.
These traps heat and make the unstable fluid to boil or otherwise convect. Thus the hot materials from sun’s centre rises get cooled and immediately plunge back downward to absorb more heat from the radiative zone. This convective motion appears to us as solar granules (grain like structure)
Since, sun has no solid layers; the distinctions between these layers are indistinct.
Solar Atmosphere (Exterior)
Now, the exterior of sun is classified into various atmospheres starting from the visible solar surface upwards. These layers are known as the photosphere, the chromospheres and the corona.
The visible disc of the Sun is considered as the base of photosphere. This is the innermost layer of solar atmosphere to which our vision can penetrate.
Since the gases are denser beyond this layer, our vision is obstructed and becomes opaque for us. So, below this region sun is opaque.
Thickness of the photospheric layer which extends from transparent to opaque layer is in the order of just 200-300km. Light emitting from the edge of the sun disc emerges from the upper and cooler layers of photosphere, that is why these part appears more dimmer than the brighter central part of the sun.
Limb darkening
The phenomenon we discussed above, where surface of the Sun appears darker in comparison to the body is called limb darkening. The temperature decreases as we move from lower to upper photospheric layers.
As we reaches chromosphere there is a sudden sharp increase in the temperature. Chromosphere is the second major layer of solar atmosphere.
Here, the gas density and intensity of radiation in this region is very low. But, temperature increases with increase in radius of the layer. Due to this high temperature most of the atoms are in the ionized state and also particles in this region have a very high velocity.
The layer chromosphere is visible to us during a total solar eclipse when the photosphere is completely concealed by the moon.
Above the hot chromosphere region we have the solar corona. Even if solar corona is a natural extension of the chromosphere it differs greatly in account of the physical state. High ionized atoms are present here due to its high temperature.
There exist a transition region between chromosphere and corona, travelling through which temperature increases to a million degrees.
The solar corona is visible during a total solar eclipse. Before centuries, people identifies solar corona but believed it as an optical illusion.
French physicist B.Lyot using his newly invented instrument called coronagraph took successful pictures of solar corona in 1930. This great discovery helped even the people of today to analyze and observe inner corona even in the absence of solar eclipse. But, to observe outer corona, the presence of solar eclipse is necessary.
Reactions inside the Sun
Now, it is the time to explore one of the most violent reactions in the universe, Nuclear Fusion. At the beginning of the 20th century there was no appropriate explanation for the abundant energy radiated by the Sun.
When we split atoms it’s called nuclear fission and the process which combines atoms are known as nuclear fusion. Nuclear fusion is the energy source of the Sun and the stars.
Through nuclear fusion, mass is converted into plenty of energy. But in the sun which is those particles involved in the reactions? Yes, the hydrogen fuses to produce helium. It sounds simple! Do you think the most violent reaction of the universe may end up that simple? Never!
Energy Production Inside
As we know hydrogen is a proton, positively charged. Recall one of the basic sentences in physics. ‘Different charges attract each other while identical charges repel’. Here, what fuses are hydrogen of same charge, they must come closer and fuse.
Enormous amount of heat and pressure which forces them to do this can only make this happen. It is already mentioned that 99% mass of the entire solar system is concentrated in the Sun.
The whole mass pulls the Sun with a huge gravity, which a human being cannot imagine. Thus, the heat and pressure paves the way to nuclear fusion to occur.
Sun is powered by the nuclear fusion reaction where four hydrogen nuclei fuse to produce one helium nuclei and two positrons. The mass of the resulted nuclei is less than the mass of the four hydrogen nuclei, where the lost mass is converted into energy.
For the fusion process to occur a very high temperature is required, here in the sun the process occurs at a temperature of 14 million Kelvin. Every second, 5 million matters are being converted into energy which is brilliant.
Final Words About the Sun
Sun is a beautiful star of medium size and belongs to G type. Since lifespan of G type stars are calculated to have nearly 10 billion years of life, the case is applicable to the Sun too.
As we know, the Sun took birth 4.5 billion years ago and is still in the stable position. But, we cannot forget the fact that Sun will not last for infinity. Like all other stars, Sun will also run out of fuel and eventually die.
When we say the Sun dies, it just doesn’t disappear when fuel exhausts. The power of gravity which pulls the sun inwards and radiation pressure that pulls the sun outward is in a balance.
Once the hydrogen inside the sun’s core is used up, this outward pressure decreases and gravity make the sun to collapse and become a red giant engulfing nearby planets. Then the collapsed gravity makes this shrink into a tiny white dwarf with enormous density and strongest gravitational field. When this white dwarf, with shimmering core, cools down, it will become an inert object called black dwarf. The end!
Conclusion
Sun, our home star is the backbone of our existence. One cannot imagine a world without sun. It controls the motion of every member of solar system directly or indirectly.
As we said when sun expands into a red giant star, earth will also get dragged into its expansion. But, studies show that even before Sun’s expansion, changes in the sun can cause catastrophic effect to our planet.
Luminosity of the sun increases by 10% every billion years and this increased heat will have a tragic impact on us. It’s time for humans to find a habitable zone before the peaceful sun appears as a red giant.
Sun is Our Energy Source. And Sun is our Only hope. Start Learning its life.