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• Star formation and evolution

  Fundamental processes in astrophysics that describe how stars are born, evolve, and eventually reach the end of their lives
• Star Formation


  1. Formation of protostar

  2. Main sequence phase
• Molecular clouds


  Dense regions of interstellar gas and dust where stars form
• Formation of protostar


  1. Gravity causes molecular clouds to collapse

  2. Rotating, flattened disk with a central condensation called a protostar forms
• Nuclear fusion


  The protostar continues to accrete material from the surrounding disk until it reaches a critical temperature and pressure for nuclear fusion in its core
• Main sequence


  A stable star is born and enters the main sequence phase, where it fuses hydrogen into helium in its core. This phase lasts for most of a star's life.
• Star Evolution


  1. Hydrogen burning

  2. Evolution for different mass stars

  3. Post-main sequence phases

  4. Death of stars

  5. Life after death
• Main sequence


  The star remains in this phase as long as it has hydrogen fuel in its core. The mass of the star determines its temperature, luminosity, and how long it stays on the main sequence.
• Evolution for different mass stars


  • Low-mass stars (e.g., Sun)
  • High-mass stars
• Low-mass stars (e.g., Sun)


  • Expand into red giants, shedding outer layers, eventually become white dwarfs, gradually cooling over billions of years
• High-mass stars


  • Burn through their fuel much faster, go through multiple stages, fusing heavier elements in their cores, can become supernovae, neutron stars, or black holes
• Post-main sequence phases


  1. Red giants and supergiants

  2. Helium burning
• Death of stars


  1. Supernova

  2. Formation of compact objects
• Life after death


  1. Planetary nebulae

  2. Formation of new stars and planets
• The life cycle of a star is a dynamic process involving the interplay of gravity, nuclear fusion, and the balance between radiation pressure and gravitational forces
• Different mass stars follow distinct evolutionary paths, ultimately shaping the composition of the cosmos
• Spherical Earth


  Proposed by ancient Greek philosophers
• Pythagoras


  • Influential figure in ancient Greece, known for work in mathematics and philosophy
  • Proposed Earth was a sphere based on observations of celestial phenomena, particularly during lunar eclipses
• Plato


  • Student of Socrates, founder of the Academy in Athens
  • Presented concept of a spherical Earth at the center of the universe, surrounded by concentric celestial spheres
• Aristotle


  • One of the most influential philosophers in history
  • Presented empirical evidence supporting the idea of a spherical Earth, based on observations of lunar eclipses and changes in star positions
• Eratosthenes


  • Polymath, chief librarian at the Library of Alexandria
  • Measured the Earth's circumference with remarkable accuracy using simple geometry and observations of the Sun's angle at different locations
• These ancient Greek philosophers not only proposed the idea of a spherical Earth but also provided empirical evidence and mathematical reasoning to support their claims
• Their contributions laid the foundation for the scientific understanding of the Earth's shape and its place in the cosmos, influencing later generations of scientists and thinkers
• Astronomical phenomena observed before the advent of telescopes

  • Planetary motion
  • Eclipses
  • Phases of the Moon
  • Comets
  • Meteor showers
  • Galactic structure
  • Variable stars
  • Celestial events
• These observations, made without the aid of telescopes, laid the foundation for our understanding of the cosmos and were instrumental in the development of early astronomy and the subsequent refinement of astronomical models and theories