The Sun

If you were a visitor from another galaxy, chances are that you would pass it without even noticing. Ah, that's just another unremarkable, average sized star, you'd think. But for us, this average sized star is remarkable. We need it to survive, because this star is our sun. Each day the sun bathes Earth in light.

Sunlight keeps us warm. It drives the weather, and provides energy for plants. The sun is far from Earth, 150 million kilometers away. It takes more than eight minutes for a beam of light to travel from the sun to the Earth. The sun is a lot bigger than it appears for Earth.

If the sun was the size of a basketball, Earth would be the size of a pinhead. It's not just the volume, the sun is pretty massive too. It accounts for 99.9% of all mass in the entire solar system, and with a great mass comes great gravity. The sun's gravity holds the solar system together. That's what keeps the Earth and other planets revolving around the sun, but the sun itself is affected by this enormous gravity more than any other celestial body.

Inside the sun at the core, it causes a pressure so powerful that the atoms themselves are mashed together, turning into other elements with a larger mass. This process is called fusion. Most of the sun is made up of hydrogen and when hydrogen nuclei are fused together, they form helium. But that's not all. When fusion turns a lightweight element into a heavier one, the process also releases huge amounts of energy in the form of light, heat, and radiation.

Fusion is the process that makes a star shine. Into that shining surface of the sun is really hot, 5,500 degree Celsius. That's so hot that any material you could possible build a spaceship from would boil and vaporize before you even come close. Inside the sun, it is even hotter. It is so hot that the atoms can no longer hold their own electrons.

With electrons missing, the atoms become ions. This hot mix of ions and free electrons is not a gas. It's the fourth state of matter, plasma. The sun is a giant rotating ball of hot plasma. This ball of plasma generates a strong magnetic field, one that extends throughout our solar system.

As the sun rotates, the magnetic field on the surface changes. Places with increased magnetic activity are seen as spots that are darker and cooler. As magnetic energy builds up in the sun spots, blasts of energy are sometimes released, like that one. These are called solar flares. Solar flares shoot particles and electromagnetic radiation so far out in space that they disturb radio signals and electronic devices on Earth.

Charged particles released by the sun move into the solar system. Luckily, Earth's magnetic field and atmosphere protects us from most of them. But near Earth's poles, streams of charged particles can enter the atmosphere, and collide with the molecules in the air. These collisions lead to incredible light shows visible at nights. Near the North Pole, they are called the Northern Lights, or the Aurora Borealis.

And near the South Pole, they are called the Southern Lights, or Aurora Australis. The sun is pretty old. It has been around for some 5 billion years. Right now, it is about halfway through its lifetime. When the sun has used up all of its hydrogen and fused it into heavier elements, it will expand rapidly, engulfing Mercury, Venus, and even Earth.

After that, it will shrink into a small dim star, a white dwarf. But don't worry. Before that happens, we get to enjoy the light and the heat from the sun for another 5 billion years.