INTRODUCTION

Our Sun lies as the very heart of our Solar System. From its tremendous light output, all the planets, the Moon, asteroids and comets, all shine brightly by simple reflection. Continuously and constantly generated in the Sun is prodigious energies, allowing for the Earth’s stable environment, harbouring and sustaining all terrestrial life.

Importantly, our Sun is simple star, similar to all the ones appearing in the nighttime sky. Obviously, the difference is that the Sun is very much brighter due to its near proximity to the Earth. The next nearest star is nearly 40,000 times the distance between the Sun and the Earth, being the Alpha Centauri triple system, where Proxima Centauri now happens to be just slightly closer at 4.3 light-years. Some other stars we see in the night sky are similar to the Sun, but the vast majority are hotter or cooler, larger or slightly smaller, brighter or less luminous.

Within our Milky Way galaxy, astronomers consider our Sun as just an ordinary yellow dwarf star with no particular outstanding or unusual peculiarities. It has no favourite position among all the stars. Having the smaller mass like the Sun does produces one huge advantage, as the energy will last between eight and ten billion years. This is unlike the largest stars, which have much shorter expected lifetimes. Our Sun, at present, is only about halfway through its evolution, and still lies with 80% of known Main Sequence stars. In the far distant future, several billions of years from now, the Sun will gradually begin swell in size, to enlarge itself into a red giant that is roughly the size of the Earth’s orbit.

The Sun over historical times does have slightly fluctuation in brightness. This has almost certainly contributed to the Ice Ages that are known to have occurred many times from changes in ice cores or geological records. Earth’s present warm climate might also be affected by other short-term changes like the solar cycle or numbers of sunspots visible on the disk.

Comprising the outer observed atmospheric ‘surface’ is the photosphere, whose effective temperature is 5778K. In the central radiative core, this temperature rises to an approximated fifteen million degrees or fractionally more. The volume of the solar sphere occupies a ball of very hot gases that is primarily made from two main elements; Hydrogen (73.46%) and Helium (24.85%). This makes up 98.21% of the solar mass, with the remaining 1.79% being all the other chemical elements.

Our knowledge of the working and nature of the Sun are based by averaging several astrophysical ‘standard’ models that have been constructed. These are supposed to explain the long history of the Sun, including composition and energy generation. Most of the bulk of the Sun is a radiative zone, that emits the energy but does not produce it. About 95% of the energy is produced in the core that is only 10% of the solar radii. In the core too, is only about 10% of this entire solar mass ever undergoes hydrogen burning by fusion, but due to the vast quantities of available hydrogen, the nuclear timescale generating energy by this mechanism is about 10¹⁰ years, while the Sun being still remains radiative and luminose is about 10¹⁰ years.

Here are the greatest temperatures and pressures, whose values are postulated to be 15.68 million degrees and ten billion atmospheres. Density of the Sun averages about 1.4 g.cm.^-3, but the core density is about 150 g.cm.^-3 or 150,000 kilograms each cubic metre. Some models are further complicated by the solar neutrino problem, which is seemingly too small in number against most predictions. [See a more Detailed Discussion on the internal nature of the Sun appears in Structure of the Sun : Part 2.]

MYTHOLOGY

In many of the early human cultures, the people openly and reverently worshipped the Sun as their supreme deity or god. Most of this devotion gave thanks for its glorious rays of warm light, whose appreciation and daily grace allowed all the peoples of the Earth to continue to live and thrive. No doubt there was always some real fears that if the Sun was not properly honoured or appeased in some way, then the sun god may become angry enough to extinguishing its important light — plunging the Earth into permanent darkness. The occasional solar eclipse probably perpetuated this idea, that always seemingly threatening to consume its light forever.

In the Middle-eastern countries the most influential early gods was the Mesopotamian god Utu or Shemash and the Hittite Arinna or Hebat. Later in Persia, the god was Mithras To the Indian Hundu, the god was Surya. In South America, the Incas called their sun god Inti, while to the Aztecs he was Tonatiuh or Huitzilopochtli.

For the Ancient Egyptians the sun god was Re or Ra, whose usual headdress adorns a large red solar disk. For a short time under the renegade pharaoh Tutmosis IV, this Egyptian god was the Aten. Later they changed the single god into three different names that depended on the place of the sun in the sky; namely, Khepri when rising from the east, Ra at midday, then Atum when the sun was setting.

To the Ancient Greeks he was Helios or Hellus, and for the Romans, Apollo, being the son of Zeus/ Jupiter with his sister Selene / Diana (The Moon). In a broadly held legend, he would daily ride his brilliantly illuminated chariot across the sky under the power of his four powerful celestial horses; which the Greeks named Pyrious, Aeos, Aethon and Phlegon. Religious veneration of the sun god occurred each year on 9th August, either at the main temple at Delphi or at the dedicated shrine in the Circus Maximus. By the 1st Century A.D., the Romans had changed their sun god to Sol Invictus (the literal “unconquered sun”) Sol, which probably originated in Syria. Quite separate from Apollo, Sol was to be adopted into the Roman pantheon of gods and was worshipped at the temple of Campus Agrippae in Rome until the rise of Christianity in the latter half of the 3rd Century. Sun worship finally ended at the fall of the Roman Empire.

ENERGY GENERATION

Matter within the solar core is very unlike anything within the Solar System. It exists in the environment of very high temperatures and pressures as ultra-hot plasma, often described as the fourth state of matter. Electrons that normally orbiting around the atomic nuclei, are easily taken away under these conditions, leaving highly ionised nuclei. Most of these highly positively charged nuclei repel or deflect from each other by the atomic strong nuclear force. A few of these atomic particles can crash energetically together, sometimes hitting so hard that the kinetic energy overwhelms the strong nuclear forces forcing them to fuse, creating heavier atoms as different chemical elements. This is the important energy generating process known as fusion, while simultaneously creating elements generally referred to in astronomy as nucleosynthesis.

Within the solar core dwell vast stores of hydrogen. Here several million tonnes of hydrogen converts to the heavier helium each second, whose dynamism creates copious amounts of energy. In the core, only a very small percentage of the atomic mass is destroyed, whose net outcome liberates stupendous amounts of energy. Generated solar energy totals 6×10²⁶ Watts each second, and converting 4.3 tonnes each second. In this particular view, the Sun is really one gigantic power plant of light and heat.

Discovery of these huge liberated energies made by fusion was found by Albert Einstein in 1905 through his famous mass-energy equivalence equation E =m×c² (energy equals mass times the speed of light squared), as first published in the landmark paper; “Does the inertia of a body depend upon its energy-content?” With a typical 600 MW (megawatts) nuclear power station, our Sun produces 10¹² MW — or one trillion times more energy every second!

If just one single gram (1.0 g.) of matter were converted into pure energy, the total power released is equal to twenty-five (25) million kilowatt-hours or about 9×10¹⁶ Joules of energy. Comparing to the average quarterly power bill of 2,000 kilowatt-hours, this is 12,500 times more in total energy consumption. At, say, 12 cents per kW the amount (2008), this is equal to about $3,000,000 worth of consumed electricity or 50,000 consecutive power bills, and enough power for 12,300 years!

So if we based our calculations on the entire net electricity generation on Earth in 2004, by all sources, it was predicted to be 1.665×10¹³ kW-hours (or 16,650 billion kW-hours) then it would take the equivalent of converting 655 kilograms of matter into pure energy each year, 1.8 kilograms per day, or just 21 grams per second — merely using 950 trillionth of the solar energy production in the same second! Just amazing! It is interesting that this consumed energy is 1.5102×10¹³ kW.hours (15.102 trillion kW.hr.), meaning the energy lost is about 1,540 billion kW.hr or 9.3%. This significant loss is probably due to energy transmission leakage through power lines or from heat dissipation. (Source: Energy Information Administration E.I.A. Energy Statistics U.S. Government (2008)

COMPOSITION of the SUN

Hydrogen is not the only element fused this way. There are other rarer reaction conversions, but this normally requires higher core temperatures. We known they can occasionally occur at lower temperatures, but the probabilities of this happening decreases rapidly to very few reactions. Such different processes are established reactions that also known to occur in other stars. Here the Hydrogen is converted into Helium, then next is Helium into Carbon, Carbon into Silicon, and finally Silicon into Iron. Many sub-reactions can also exist. For example, Helium can convert into either Oxygen or Nitrogen, or rarely, as Fluorine, etc. Simplistically, the Sun is an element generating chemical factory, manufacturing all the common elements that are found on the Earth and within the human body.

Once these energies reach the solar surface, it radiates light equally into space in every direction. Our Earth receives only a very tiny fractions of this energy, but despite the distance of about 150 million kilometres, the amount received is so intense that the retina can be quickly damaged causing irreparably and permanent blindness. Also ultraviolet radiation exposure begins to disrupt external body cells like skin.

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Last Update : 23rd July 2018

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