Sen—The Sun, which is the only star we can examine close up, was born about 4.6 billion years ago. Material in a cloud of gas and dust slowly clumped together creating a hotter and hotter mass that eventually ignited.
The Sun, a type of star termed a yellow dwarf, influences all objects in the solar system. Its gravitational influence results in the orbit of the planets, comets, asteroids and dwarf planets - and stretches out billions of kilometres to the Oort cloud.
The Sun's heat and light created and sustain life on planet Earth. But it does not burn in the ordinary sense, operating instead as a cosmic nuclear power station.
The Sun is an average sized star. Relative to Earth and the other objects in the solar system though it is huge - 1,400,000 million kilometres (865,000 miles) in diameter, which is over 100 times the diameter of Earth.
The Sun is made of helium and hydrogen in a state known as "plasma" - a gas which is mainly made of atoms stripped of their electrons. It converts four million tons of hydrogen into helium a second.
The Sun's "structure" consists of its core, its surface (photosphere), its corona and its solar wind. The entire structure, known is its heliosphere encompasses everything in the solar system and stretches out to approximately 17 billion km where the solar winds hit interstellar space. At this point, known as the heliopause, the Sun's solar winds hit the stellar winds of other stars
The Sun's core reaches temperatures of 15 million degrees Celsius.
The Sun's photosphere (visible surface) has temperatures in the region of 4,000 to 6,000 degrees Celsius. The coolest parts of the Sun's photosphere are the sunspots which have temperatures of about 3,000 to 4,500 degrees Celsius and appear dark because they are substantially cooler relative to the surrounding area of the surface. Sunspots are caused by complex magnetic activity that interfere with the flow of heat from the core to the surface. Sunspots may appear small relative to the surface area of the Sun but in fact can be tens of thousands of miles across and some are many times larger than planet Earth. They can last from hours to days and are more frequent in some years than in others as the Sun goes through an 11-year cycle of activity. Seen in close-up, the photosphere has a honeycomb structure caused by the churning convective currents.
(Warning: Studies of the Sun are made with specialised equipment and one should never look directly at it with any optical instrument without professional-standard filters as severe eye damage may result).
Although the Sun at a distance looks like a perfect yellow ball (and it is almost a perfect ball shape), the Sun has an atmosphere known as its "corona" which reaches out more than 1,000,000 kilometres, The Sun's corona is actually hotter than the surface and can be hotter than the core of the Sun with the corona reaching temperatures of up to 20 million degrees Celsius. The Sun's corona can be seen clearly during a total solar eclipse, which is the only time when it is safe to look directly at the Sun..
Although the corona stretches only 1,000,000 kilometres, escaping from the Sun is the solar wind whose particles travel at extreme speeds (1 million kilometres per hour) and travel seventeen billion kilometres (11 billion miles) to interstellar space.
The solar wind is made of incredibly fast electrically charged particles that escape the Sun's gravity and travel at great speeds until they reach interstellar space. Earth is protected from the solar winds by its magnetosphere, an electromagnetic sphere the surrounds the earth (due to the Earth having an iron core).
The Sun is expected to continue in its present form for another 5 billion years, meaning it is about half way through its life. After 10 billion years the Sun will have run out of fuel and it will collapse under its own mass - almost like a re-birth - and ignite into a much larger and brighter star than it is today, engulfing the orbits of the inner planets. As the Sun gets larger its outer temperature will cool and appear red. The final phase of the end of the Sun will see it shrink back from a big red star to a small white star with a cooling core which will glow faintly. By the end of the Sun's life, humankind and other life on Earth will only continue it we have found another star to live by, or created space transporters that can sustain life.