Sun is a star and it is considered the center of the solar system galaxy. The sun is much more than just the gravitational center of our galaxy. In truth, it is the center of life for our world. Every living thing on Earth is in some way sustained by the energy given off by the sun.
What makes the sun so bright is its power source: a process called nuclear fusion, which yields abundant energy.
The Sun is a ball of glowing gas. The sun consists primarily of hydrogen and helium gas. The fusion reaction, along with the sun’s enormous size, means it will continue to shine brightly billions of years into the future.
The sun provides the Earth with lights, warmth and energy although it is about 93 million miles away from earth.
The sun has many layers, each of which has a characteristic temperature. The center, called the core, is where most of the fusion takes place; scientists estimate its temperature at 15 million degrees Celsius which is 27 million degrees Fahrenheit. The surface, called the photosphere, is the brightest part of the sun, although it is much cooler, about 6,000 degrees Celsius which is more than 10,000 degrees Fahrenheit.
The following video also explains reason for the Sun to be so bright in simple words. Click here.