Guest Author - Lea Terry

Measuring over 330,000 times the size of Earth, the Sun is the largest object in the solar system. And though it constitutes over 99 percent of the solar system’s mass, when compared to the other 100 billion stars in the galaxy, it is actually of average size. Still, without it, life on Earth could not exist.

Located about 93 million miles away from Earth, the Sun is the closest star to our planet. Not only does it keep the planets in orbit, the Sun also controls the seasons, ocean currents and weather on Earth. And because it is responsible for photosynthesis in plants, the Sun is also the ultimate source of all food.

The Sun is an ever-changing mass of gases, primarily hydrogen and helium, which comprise approximately 98 percent of the Sun’s mass. More than 60 other elements--including oxygen, carbon, nitrogen, silicon, magnesium, neon and iron--are also present, though in very small amounts.

The Sun has several layers, with temperatures that range from 28 million degrees at the core to over 9,900 degrees Fahrenheit at its surface. In the innermost region, the core, energy is created through a process called nuclear fusion, in which hydrogen atoms are fused into helium. About 383 billion trillion kilowatts of energy is generated, an amount equal to 100 billion tons of TNT being detonated every second. When this energy reaches the Sun’s surface, it creates the light that we see. The next two regions, the photosphere (this is the part of the Sun we can see) and the chromosphere, transmit energy from the core to the Sun’s outer surface. The outermost region, the corona, reaches several million miles into space, and is only visible during a total eclipse.

The Sun is estimated to be around 4.6 billion years old, which is between 10 million and 20 million years older than Earth. Scientists believe the Sun can produce energy for about 10 billion years, and so is about halfway through its life cycle. Because the Sun’s radius is gradually increasing, it will eventually expand so much that it will swallow up nearby planet Mercury. The Sun will evolve into what is called a red giant, a star that has burned up all or most of its hydrogen. After this, the Sun’s atmosphere will disappear, leaving behind the core, which at this point is called a white dwarf. Within a billion years from today, changes in the Sun’s structure will lead to the evaporation of the oceans and the disappearance of the polar ice caps, making Earth unable to support life.

Because of its power and beauty, the Sun has also been a source of fascination throughout the centuries. Many civilizations saw the Sun as a god--for the Egyptians it was Ra, for the ancient Greeks, it was Apollo. Several kings throughout history even claimed to be descended from the Sun. In many ancient civilizations, it was believed the Sun was the largest and most powerful of all the celestial bodies. Though we now know that the Sun is actually average, as far as stars go, we also know for certain that its energy is what enables life to exist on Earth.