Key Facts About Sun and Solar System
Sun is a star with a diameter of 109 times of earth and a mass of 3.30 lakh times of Earth, roughly accounting for 99.9% of total mass of the Solar system. Sun is mostly made of Hydrogen and Helium and is a main sequence yellow dwarf. It was formed some 4.6 billion years ago and is expected to deplete its hydrogen in next 5-6 billion years to turn into a red giant at the end of its life.
Structure of Sun
The Sun has a core at its center; a radiative zone surrounding the core; a convective zone surrounding the radiative zone; a thin photosphere at its surface; and a chromosphere and corona that extends beyond the photospheric surface.
Each of these zones are briefly discussed here:
Core
Solar energy is produced at the core of the sun where temperatures reach 15 million °C by nuclear fusion. This enormous energy makes the sun shine.
Radiative Zone
Energy produced in core slowly rises in the radiative zone outside the core. It takes around one million years for energy to travel out of the radiative zone.
Convection Zone
Convection zone is just beneath the Sun’s surface.
Photosphere
Photosphere is the visible surface of Sun where temperature is around 5500°C. This part gives us light, which takes around 8 minutes to reach from sun to earth.
Chromosphere
Chromosphere is a thin layer of gas above the photosphere. Along with Corona, it makes the atmosphere of Sun.
Corona
Corona is a thick layer of gas above chromosphere. It extends millions of kilometers around the sun. Corona and Chromosphere are visible during a total solar eclipse when the sun’s surface is completely hidden behind moon.
We note here that Corona is much dimmer than the rest of the Sun, and can only be seen when the Sun is blocked from view—either by a scientific instrument called a coronagraph, or naturally during a solar eclipse. Even though it is thinner than the best laboratory vacuums on Earth and so far away from the Sun’s core, the corona is very energetic and very hot, with its plasma reaching temperatures of millions of degrees. The scientists still have not been able to figure out how the corona gets so hot. Current research suggests that the strong electrical currents and magnetic fields in and around the Sun transfer tremendous amounts of energy to the corona, either generally or by special “hotspots” that form for short periods of time and then disappear again.
Composition of Sun
The Sun’s mass is composed of 71 percent hydrogen, 27 percent helium, and 2 percent other elements.
In terms of the number of atoms in the Sun, 91 percent are hydrogen atoms, 9 percent are helium atoms, and less than 0.1 percent are atoms of other elements. Most of the stars in the universe have a similar chemical composition.
Mass of Sun
The Sun has a mass of 1.99 million trillion trillion kilograms. The most massive supergiant stars have about one hundred times more mass than the Sun. The least massive dwarf stars and brown dwarfs contain about one-hundredth the mass of the Sun.
Rotation of Sun
Sun rotates about its axis from west to east. Since the Sun is not a solid object but rather a big ball of electrically charged gas, it spins at different speeds depending on the latitude.
The Sun spins once around its axis near its equator in about 25 days, and in about 35 days near its north and south poles. This kind of spinning, in which different parts move at different speeds, is called differential rotation.
Implications of Sun’s Spin
- Magnetic fields in the Sun, created by strong electric currents, are produced because of the Sun’s spin.
- Since Sun has differential rotation, and its interior roils with tremendous heat and energy, the magnetic field lines in the Sun get bent, twisted, knotted, and even broken; sunspots, prominences, solar flares, and coronal mass ejections are the result.
Formation of Solar System
The solar system is thought to have developed by the so called nebular hypothesis {given by Simon de Laplace}. About 4.6 billion years ago, the Sun formed from a large cloud of gas and dust that collapsed upon itself because of gravitational instability. When the Sun was born, not the entire nebula of gas and dust that had been gravitationally gathered was incorporated into the Sun itself.
Some of it settled into a disk of orbiting material. As this material orbited in a protoplanetary disk, numerous collisions between the tiny grains led to some of the grains sticking together, making larger bodies. After millions of years, the largest bodies—planetesimals—had sufficient mass (and hence gravity) to start attracting other objects in the disk to them.
Growing larger and larger, these planetesimals became protoplanets; the largest protoplanets grew larger still, until at last the planets were formed.
Although the solar wind has removed much of the remaining, unprocessed gas and dust, numerous smaller objects (and some of the gas and dust, as well) still remain today, providing the rich variety of objects and phenomena in a solar system more than four and a half billion years later.
Size of Solar System
Solar system reaches out to the orbit of the most distant planet, Neptune, or about five billion kilometers away from the Sun. Beyond Neptune is the Kuiper Belt, a thick, doughnut-shaped cloud of small icy bodies that extends to about eight billion miles (12 billion kilometers). Beyond Kuiper belt is the Oort Cloud, which is a huge, thick, spherical shell thought to contain trillions of comets and comet-like bodies. The Oort Cloud may extend as far as a light-year out from the Sun.
Thus, Solar system is generally divided into five major zones:
- the inner (or terrestrial) planet zone,
- the asteroid belt,
- the outer (or gas giant) planet zone,
- the Kuiper Belt, and the
- Oort Cloud.
There is no exact boundary for these zones, however, and their sizes are not well determined; there is also overlap, in the sense that objects from one zone often appear in another zone.
