Star Lifespan: Stars evolve over time, using up their fuel from birth to death. • Low Mass Stars: 85% of stars in the Milky Way are low mass stars, like the Sun, and have relatively uneventful lifespans. • High Mass Stars: High mass stars, while less common, play a crucial role in the universe by creating heavy elements. • Brown Dwarfs Characteristics: Objects with masses between 0.01 and 0.08 solar masses, never initiating hydrogen fusion in their cores. • Red Dwarfs Characteristics: Stars with masses between 0.08 and 0.25 solar masses, fusing hydrogen in their cores and constituting the majority of stars in the Milky Way. • Sun-like Stars Life Cycle: Stars with masses between 0.25 and 4 solar masses, evolving from protostars to red giants, eventually becoming white dwarfs. • Star Lifespan: The lifespan of a main sequence star is determined by its mass and the amount of hydrogen it has to fuse. • Sun’s Lifespan: The Sun’s hydrogen-burning lifespan is approximately 10 billion years. • Red Dwarfs: Red dwarfs, the dimmest and most common stars, can live up to 10 trillion years due to their low mass. • Sun’s Lifespan: The Sun will be a main sequence star for about 11 billion years, currently 4.5 billion years into its lifespan. • Sun’s Future Stages: After exhausting its hydrogen fuel, the Sun will expand into a red giant, then a horizontal branch star, and finally a white dwarf. • Age Determination: The age of the Sun is determined by the ages of carbonaceous meteorites, which are about 4.567 billion years old. • Sun’s Energy Source: The Sun primarily generates energy through hydrogen fusion, with a small percentage (2%) from the CNO cycle. • Sun’s Core Structure: The Sun’s core consists of an inert helium core surrounded by a hydrogen-burning zone, with energy transport primarily radiative in the core region. • Main Sequence Lifecycle: During the main sequence, the Sun maintains a balance between gravitational collapse and outward pressure from nuclear fusion in its core. • Star Expansion and Contraction: Stars expand when they generate heat from fusion and contract when they cool down. • Equilibrium in Stars: Stars maintain a balance between the inward pull of gravity and the outward pressure from fusion, known as hydrostatic equilibrium. • Main Sequence and Equilibrium: During the main sequence phase, stars achieve a balance between energy output and energy loss, resulting in a stable size. StarEvolution LowMassStars StellarLifecycle RedGiant WhiteDwarf Astrophysics SunLifecycle StellarSimulations PlanetaryNebula Astronomy Key themes and topics emphasized include: StarEvolution, LowMassStars, StellarLifecycle, RedGiant, WhiteDwarf, Astrophysics, SunLifecycle, StellarSimulations, PlanetaryNebula, Astronomy.