Monday, 1 December 2014

OUR SUN: Fascinating facts                        

Our Sun is the star at the center of our Solar System. No. It is not a sphere. It is more spherical and consists of hot plasma that is interwoven with magnetic fields.

It has a diameter of about 1,392,684 km (865,374 mi), around 109 times that of Earth and its mass (1.989×1030 kilograms, approximately 330,000 times the mass of Earth) and it accounts for about 99.86% of the total mass of everything else in our Solar System.         

Chemically, about three quarters of the Sun's mass consists of hydrogen, whereas the rest is mostly helium. The remaining 1.69% (equal to 5,600 times the mass of Earth) consists of heavier elements, including oxygen, carbon, neon and iron, among others on a smaller scale.                    

The Sun formed about 4.567 billion years ago from the gravitational collapse of a region within a large molecular cloud. Most of the matter gathered in the center, whereas the rest flattened into an orbiting disk that would later become our Solar System. The central mass of our sun became increasingly hot and dense, eventually initiating thermonuclear fusion in its core. It is believed by scientists that almost all stars are formed by this process. The tremendous power output of the Sun is not due to its high power per volume, but instead due to its large size. Think of it as a large compost pile. A small pile won’t generate heat but a large one will.

In its core, the Sun fuses about 620 million metric tons of hydrogen each second. The Sun's power (about 386 billion billion mega Watts) is produced by nuclear fusion reactions. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium.

The core of the Sun is considered to extend from the center to about 20–25% of the solar radius. It has a density of up to 150 g/cm (about 150 times the density of water) and a temperature of 15.7 million degrees Kelvin. It is much more in Fahrenheit and Celsius. To give you some idea of just how hot the core of the Sun is, this interesting little tidbit will excite you. If a piece of the core of the Sun the size of a pinhead was 100 miles (160 km) in space from Earth, everyone and every animal on the surface of Earth immediately below it would be incinerated. As the Earth turns, a huge wide swath of Earth would be incinerated. Every second in the core of the Sun, the fusion explosions are equivalent to 10 billion hydrogen bombs.

The Sun and everything in our solar system orbits the center of the Milky Way at a distance of approximately 24,00026,000 light-years from the galactic center, thereby completing one clockwise orbit, as viewed from the galactic north pole, in about 225–250 million years.  That gives you some idea of how large our galaxy is.

The average distance of Earth from the Sun is approximately 1 astronomical unit (about 150,000,000 km; 93,000,000 mi), though the distance varies as Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds. 

The energy of our sun in the form of light supports almost all life on Earth by photosynthesis and also drives Earth's climate and weather.

The deadly gamma rays (high-energy photons) released in fusion reactions are absorbed in only a few millimeters of solar plasma and then re-emitted again in a random direction and at slightly lower energy. Therefore it takes a long time for radiation to reach the Sun's surface. Estimates of the photon travel time range between 10,000 and 170,000 years to reach the surface of the Sun.  It would be like walking ten steps forward and retreating nine point nine steps backwards. In contrast; it takes only 2.3 seconds for the neutrinos, which account for about 2% of the total energy production of the Sun, to reach the surface of the Sun.  

During the final part of the photon's trip out of the Sun, in the convective outer layer, collisions are fewer and far between, and they have less energy. The photosphere is the transparent surface of the Sun where the photons escape as visible light. Each gamma ray in the Sun's core is converted into several million photons of visible light before escaping into space. Neutrinos are also released by the fusion reactions in the core, but unlike photons they rarely interact with matter, so almost all are able to escape the Sun immediately. Neutrons are so small, they can actually slip through lead which gamma photons cannot do. They are everywhere in space and every second of our lives; billions of them enter our bodies and exit them without ever hitting any of the atoms that our bodies are made of.  

Solar material is so hot and dense enough that thermal radiation is the primary means of energy transfer from the core. This zone is not regulated by thermal convection; however the temperature drops from approximately 7 to 2 million Kelvin with increasing distance from the core.

This temperature gradient is less than the value of the adiabatic (a process or condition in which heat does not enter or leave the system concerned) lapse rate and hence cannot drive convection. Energy is then transferred by radiationions of hydrogen and helium emit photons, which travel only a brief distance before being reabsorbed by other ions.

In the Sun's outer layer, from its surface to approximately 200,000 km below (70% of the solar radius from the center), the temperature is lower than in the radiative zone and heavier atoms are not fully ionized. As a result, radiative heat transport is less effective. The density of the plasma is low enough to allow convective currents to develop. Material heated at the tachocline that is the transition region of the Sun between the radiative interior and the differentially rotating outer convective zone. It is in the outer third of the Sun). It picks up heat and expands, thereby reducing its density and allowing the temperature to rise.

As a result, thermal convection develops as thermal cells carry the majority of the heat outward to the Sun's photosphere. Once the material cools off at the photosphere, its density increases, and it sinks to the base of the convection zone, where it picks up more heat from the top of the radiative zone and the cycle continues over and over again. At the photosphere, the temperature has dropped to only 5,700 Kelvin.  

The surface of the Sun, called the photosphere, is at a temperature of about 5800 K. Sunspots are "cool" regions, only 3800 K (they look dark only by comparison with the surrounding regions). Sunspots can be very large, as much as 50,000 km in diameter. Sunspots are caused by complicated and not very well understood interactions with the Sun's magnetic field. Tornadoes emerging from the surface of the Sun rise hundreds of thousands of miles.

A small region known as the chromosphere lies above the photosphere. The highly rarefied region above the chromosphere, called the corona, extends millions of kilometers into space but is visible only during a total solar eclipse. 

Why is the temperature millions of miles from the surface of the Sun so much hotter (two million degrees Kelvin) than the surface of the Sun which is only 5,700 Kelvin? I don’t have an answer but here is a really interesting tidbit of information for you. Back in the Dark Ages when people were burned at the stake, it was discovered that if they were hung above the flames, they would burn faster. A scientific test was shown on TV in which it was established that the heat above the flames is much hotter than the flames.  

The Sun is about 4.5 billion years old. Since its birth it has used up about half of the hydrogen in its core. It will continue to radiate “peacefully” for another 5 billion years or so (although its luminosity will approximately double in that time because the Sun will also double and later become what is called a Giant Sun. But eventually it will run out of hydrogen fuel. It will then be forced into radical changes which, is commonplace by stellar standards. It will eventually explode and probably bring about the creation of a planetary nebula however, the total destruction of the Earth will occur long before that event when the ever-enlarging Sun engulfs Earth.

Hopefully, Mankind will have found a way to leave Earth much earlier and live elsewhere. If not, as the Sun grows larger, humans and animals will be slowly dying off until Earth is nothing but molten rock and finally atoms, not unlike those of the Sun. When that happens, the only thing left of our existence is rockets we sent out into space. And it is conceivable that if anyone else in space sees one of these rockets somewhere in our galaxy, they will ask, “Where did that come from?” 

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