Sun

The Sun is the massive star located at the center of our Solar System. It is a giant sphere of hot plasma. This plasma is heated to incandescence by nuclear fusion reactions occurring in its core. The Sun radiates energy from its surface primarily as visible light and infrared radiation. It also emits 10% of its energy as ultraviolet radiation. This energy is the main source of life for everything on Earth.

At its heart, the Sun works through a process called nuclear fusion. In the core, hydrogen atoms fuse together to create helium. This happens through the proton-proton chain reaction. Every second, the Sun's core fuses about 600 billion kilograms of hydrogen. This process converts 4 billion kilograms of matter into pure energy. This energy travels from the core toward the surface.

The Sun is classified as a G-type main-sequence star. Specifically, it is a G2 star. This classification means its surface temperature falls into the second range of the G class. The Sun is a Population I star. This means it is rich in heavy elements. These elements were likely produced by previous generations of stars. Some may have even come from nearby supernovae.

Measuring the Sun reveals its incredible scale. Its diameter is approximately 1,391,400 kilometers. This makes it about 109 times wider than the Earth. The Sun is the most massive object in our Solar System. It contains about 99.86% of the system's total mass. Its mass is roughly 330,000 times that of Earth. The distance from Earth to the Sun is about 149.6 million kilometers. This distance is called an astronomical unit (au).

The Sun's composition is mostly light gases. The photosphere, or visible surface, is about 73% hydrogen and 25% helium. It also contains smaller amounts of heavier elements. These include oxygen, carbon, neon, and iron. Astronomers call these heavier elements "metals." Over time, the helium in the core has increased. It rose from about 24% to about 60% due to fusion. This helium stays in the core because it is too heavy to rise.

Scientists have studied the Sun since ancient times. People in many cultures have venerated the Sun. Today, we use the science of heliology to study it. We know the Sun formed about 4.6 billion years ago. It grew from the gravitational collapse of a large molecular cloud. Most of the matter gathered in the center to form the star. The remaining matter flattened into a disk. This disk eventually became the Solar System.

The Sun's life will change in the future. In about 4 to 7 billion years, hydrogen fusion will diminish. The Sun will lose its hydrostatic equilibrium. This will cause the core to become much denser and hotter. The outer layers will expand, turning the Sun into a red giant.

Eventually, it will shed its outer layers. It will then become a white dwarf. This is a dense, cooling star. It will no longer produce energy through fusion. It may eventually become a black dwarf. This is a theoretical, extremely dense object that gives off almost no energy.