Stars are the fundamental building blocks of the universe, shaping the evolution of galaxies and influencing cosmic phenomena on vast scales. Understanding their physics requires a detailed study of the forces governing their formation, structure, and lifecycle. Stellar physics combines principles from thermodynamics, nuclear physics, and general relativity to explain the energy production, stability, and eventual fate of stars. Observations across the electromagnetic spectrum, from radio waves to gamma rays, provide insights into stellar composition, temperature, and behavior.

At the heart of stellar physics is the balance between gravitational collapse and outward pressure. Gravity continuously pulls the stellar material inward, while nuclear fusion generates energy that radiates outward, maintaining equilibrium. This delicate balance determines the longevity of a star, with more massive stars consuming their fuel rapidly, while lower-mass stars burn slowly over billions of years. The life cycle of a star is deeply connected to its initial mass, which dictates its energy output, structure, and eventual transformation into a white dwarf, neutron star, or black hole.

Observing stars has been a cornerstone of astronomy for centuries, but modern telescopes and spectroscopy have revolutionized our understanding. Spectroscopy allows scientists to analyze starlight and determine the elements present in a star's atmosphere. By studying absorption and emission lines, astronomers can infer a star's composition, temperature, and motion. Advances in observational technology, such as space-based telescopes and high-resolution imaging, provide detailed views of stellar phenomena, revealing dynamic processes such as stellar flares, mass ejections, and pulsations.