Most of us know that the universe began with the Big Bang, an explosion of unimaginable power that flung all the matter in existence outward. From this, the wonders of space started to form. But how does our little region of the cosmos fit into all of this?
Scientists believe that the universe began to coalesce around 15 billion years ago. Back then, there were only two gases in existence, hydrogen and helium. That's it. Those two gases came together inside of stars to burn and form all of the heavier elements of the periodic table. As the stars died and exploded, they spread those elements out into space. Ten billion years of stars repeated this cycle of burning and dying, constantly forming clouds of gas and dust.
Then, around five billion years ago, an important event occurred. One of the clouds of dust, called a solar nebula, began to collapse into a swirling disk. The reason for the collapse is still unclear though the prevailing theory is that a shockwave from a nearby supernova rippled through the cloud to initiate the implosion. The gravity at the center of the disk drew more dust and gas to it, causing the gases to heat up from the pressure. Finally, at around 3000K (2726 C or 4940 F), the gases ignited and created a new star.
The remaining gases and dust of the solar cloud continued to swirl, getting cooler and shrinking in number as the new star grew. The gases eventually froze into solid particles that began clumping. In the span of a few million years, the clumped particles became large enough to be called planets.
Our Sun is by far the largest object in the solar system, containing over 99% of the entire mass in the system. However, the Sun actually is a fairly common star. Stars are classified by their size and color with medium-sized (medium in this case being 870,000 miles in diameter) yellow stars comprising a large majority of them
Like the planets themselves, the Sun is divided into different layers inside of a nearly perfect sphere. In the center is the core of the star. This is where most of the fusion that generates energy occurs. Temperatures at the core easily reach 13,600,000 K (24,479,540 F), causing hydrogen atoms to collide and fuse into helium, generating energy equivalent to 9.15 x 10^10 megatons of TNT every second. The resulting heat transfers out into the rest of the Sun through the other layers before escaping into space.
The convection zone holds 90% of the volume of the star while being much less dense than the core. Here, the temperature drops to just 4,000,000 K (7,000,000 F). Its main purpose is to maintain the pressure and temperature of the core while allowing heat to escape to the upper layers via convection. This convection also creates a slight dynamo effect, generating the Sun's magnetic field.
The visible surface of the Sun, called the photosphere, is the only place where light can be transmitted into space. Under this layer, the Sun is completely opaque. While it appears to be just the visible "skin" on the surface, the photosphere is actually tens of kilometers thick.
The corona of the Sun could be considered the "atmosphere" of the star. It expands out about 500 kilometers from the surface at an average temperature of 4,000 K at the bottom before increasing to nearly 1,000,000 K near the top. From here, the solar winds progress out into the rest of the solar system. When the solar winds encounter Earth's atmosphere at high speed, they cause the atmospheric particles to glow. This is what is responsible for the northern and southern lights at the poles.
On the surface of the Sun, there frequently forms dark spots creatively named sunspots. These are regions that, because of intense magnetic activity, are cooler than the surrounding surface as the magnetic fields inhibit convection from the lower layers. The same magnetic fields heat the overlying corona, often triggering the eruption of solar flares and coronal mass ejections. The energy given off during either of these events can greatly affect the Earth's atmosphere and, correspondingly, its weather.
Lastly are the eclipses. An eclipse happens when an object moves between the Earth and the Sun. Most commonly, this is the Moon but on rare occasions, another planet may enter that line of sight. An eclipse of the Sun is an important event. When the main disk of the Sun becomes blocked, only then can the corona be viewed and studied as it is normally unseen against the Sun's body.