What is it and how did it form?
The Sun is a star at the centre of our Solar System. The Earth and other matter (including other planets, asteroids, comets) orbit the sun. The sun accounts for 99.86% of the entire mass of the solar system and it sits at a distance of 93 million miles from Earth. Considering the scale of the galaxy, this distance is relatively short. It takes just 8 minutes for the light from the sun to reach us so, realistically speaking, when we look up at the sun, we see it as it was eight minutes ago!
109 Earths would fit across the sun’s surface and 1.3 million Earth’s would fill the sun’s interior. The Sun’s outer visible layer is called the photosphere and has a temperature of 6,000°C (11,000°F). Solar energy is created deep within the core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F).
Energy from the sun (sunlight) supports almost all life on Earth and drives the planet’s weather. Pressure is so intense inside the sun (340 billion times Earth’s air pressure at sea level) that nuclear reactions take place. This reaction causes four protons or hydrogen nuclei to fuse together to form one alpha particle or helium nucleus. The alpha particle is about .7 percent less massive than the four protons. The difference in mass is expelled as energy and is carried to the surface of the Sun, through a process known as convection, where it is released as light and heat. Energy generated in the Sun’s core takes a million years to reach its surface. Every second 700 million tons of hydrogen are converted into helium ashes. In the process 5 million tons of pure energy is released; therefore, as time goes on the Sun is becoming lighter.
The sun continuously emits charged particles (mostly protons and electrons), which are the byproducts of thermonuclear reactions occurring inside the sun. These particles take two to three days to reach the Earth and when they reach the Earth’s atmosphere they are deflected to the polar regions. The movement of these particles towards the Earth is called solar wind.
The Sun appears to have been active for 4.6 billion years and has enough fuel to go on for another five billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow the Earth. After a billion years as a red giant, it will suddenly collapse into a white dwarf — the final end product of a star like ours. It may take a trillion years to cool off completely.
A solar flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released. Radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves at the long wavelength end, through optical emission to x-rays and gamma rays at the short wavelength end. The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time! The first solar flare recorded in astronomical literature was on September 1, 1859. Two scientists, Richard C. Carrington and Richard Hodgson, were independently observing sunspots at the time, when they viewed a large flare in white light.
The Aurora Borealis (Northern Lights) and Aurora Australis (Southern Lights) are the result of electrons colliding with the upper reaches of Earth’s atmosphere. (Protons cause faint and diffuse aurora, usually not easily visible to the human eye.) The electrons are energized through acceleration processes in the downwind tail (night side) of the magnetosphere and at lower altitudes along auroral field lines. The accelerated electrons follow the magnetic field of Earth down to the Polar Regions where they collide with oxygen and nitrogen atoms and molecules in Earth’s upper atmosphere. In these collisions, the electrons transfer their energy to the atmosphere thus exciting the atoms and molecules to higher energy states. When they relax back down to lower energy states, they release their energy in the form of light. This is similar to how a neon light works. The aurora typically forms 80 to 500 km above Earth’s surface. Earth’s magnetic field guides the electrons such that the aurora forms two ovals approximately centered at the magnetic poles.