The sun is a yellow dwarf star in the center of the solar system , and it is the largest, brightest and most massive object in the system.
The sun formed around 4.5 billion years ago. At that time, the area of the Milky Way galaxy that would become the solar system consisted of a dense cloud of gas the remnants of an earlier generation of stars. The densest region of this cloud collapsed and gave rise to the protostar that would become the sun. As this young protostar grew, planets, moons and asteroids formed around it from what remained of this raw material, bound in orbit to their parent star by its immense gravity.
At the heart of the sun, this same force sparked nuclear fusion that powers the star. The heat and light from this nuclear reaction enabled life on Earth to evolve and prosper. However, this reaction will eventually lead to the sun’s demise, as the sun will eventually run out of nuclear fuel.
WHAT IS THE SUN MADE OF?
The sun is in the period of a stellar body's life in which it fuses hydrogen to create helium. The difference in mass between the hydrogen atoms and the daughter helium atom is released as energy — the heat and light that sustain our planet. This is called the main sequence.
Before the main sequence stars like the sun exist as what is known as protostars, gathering mass from their surroundings and growing to the mass required to initiate fusion.
Like all main-sequence stars, the majority of the sun's mass is made up of hydrogen, with some helium and traces of heavier elements , which are referred to as the metallicity or “Z” of a star (the astronomical definition of a metal is "any element heavier than helium").
The ratio of the sun's mass is 73% hydrogen, 25% helium, and 2% metals. The generations of stars that preceded the sun would have had smaller ratios of metals than this, enriching their galaxies with heavier elements upon their deaths.
The larger a star is, the more rapidly it burns through its hydrogen content; some of the largest stars such as those with masses 40 times that of the sun — have lifetimes as short as a million years compared to the Sun's main-sequence lifetime of around 10 billion years, according to Swinburne University of Technology in Australia
How Hot Is The Sun?
Yet the core of the sun and this powerful engine is out of sight. The deepest part of the sun that we see on Earth is the photosphere, which loosely passes as a "surface" for this ball of plasma. The temperature of the photosphere ranges from around 6,700 F to 14,000 F (3,700 C to 7,700 C).
Above the photosphere is the loose, tenuous atmosphere of the sun, known as the corona. The corona isn't visible from Earth under ordinary conditions as the light it emits is overwhelmed by that of the photosphere. The corona, however, represents one of the most significant mysteries surrounding the sun.
Scientists’ theoretical models of stars suggest they should become hotter as one moves towards their center as is seen in regions of the sun between the photosphere and core, called the chromosphere and the transition region, where temperatures rise sharply to 900,000 F (500,000 C), according to NASA
Yet, the corona at a temperature of around 900,000 F or more, is actually many times hotter than the photosphere 1,300 miles (2,100 km) below it.
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