The Sun is a star, a luminous sphere of plasma held together by its own gravity. It is one of the stars within the Milky Way galaxy. The Milky Way is a spiral galaxy, and our solar system, including the Sun and all the planets orbiting it, is located within one of the spiral arms of the Milky Way. The Sun's position within the galaxy is a key factor in understanding its properties and its place in the cosmos.

Astronomical distances are often very large, making it impractical to use units like kilometers or miles. A light-year is a unit of distance specifically used in astronomy. It represents the distance that light travels in a vacuum during one year. Since light travels at a constant speed of approximately 300,000 kilometers per second, one light-year is equivalent to approximately 9.461 x 10¹² kilometers (or about 5.88 trillion miles). This allows astronomers to express the immense distances between stars, galaxies, and other celestial objects in a more manageable way.

The life cycle of a star begins with the formation of a stellar nebula – a vast cloud of gas and dust, primarily hydrogen. Gravity causes this nebula to begin to collapse. As the cloud collapses, it spins faster and heats up, forming a protostar. This protostar continues to accrete material from the surrounding nebula, increasing in mass and temperature.

Eventually, the core of the protostar becomes hot and dense enough to initiate nuclear fusion, specifically the fusion of hydrogen into helium. This marks the birth of a stable star. The outward pressure from the nuclear fusion balances the inward pull of gravity, establishing hydrostatic equilibrium. The star spends the majority of its life in this stable phase, fusing hydrogen into helium in its core.

As the star exhausts the hydrogen fuel in its core, nuclear fusion ceases in the core. The core begins to contract, and the star expands significantly into a red giant (for stars of low to medium mass) or a red supergiant (for stars of high mass). During this phase, hydrogen fusion continues in a shell around the core, causing the star to glow red.

The fate of the star depends on its initial mass. Low to medium-mass stars (like our Sun) will eventually shed their outer layers, forming a beautiful planetary nebula. The remaining core becomes a white dwarf – a small, dense, and hot remnant of the star.

More massive stars undergo a far more dramatic end. When the core runs out of fuel, it collapses rapidly, triggering a powerful supernova explosion. This supernova explosion blasts the star's outer layers into space, creating a supernova remnant nebula enriched with heavy elements. The core of the star collapses into either a neutron star or, for the most massive stars, a black hole.

The material ejected from the supernova explosion can then provide the raw materials for the formation of new stars and planetary systems, potentially leading to the birth of new solar systems with orbiting planets.