By engaging with all the videos within this series, you will effectively complete a full undergraduate course in astronomy, equipping yourself with the knowledge and skills necessary to navigate the night sky with confidence, learning all the basics and many advanced topics! Cosmology is the scientific discipline that explores the origin, evolution, and ultimate fate of the universe. It encompasses the investigation of various phenomena, including the distribution of matter, the dynamics of galaxies, and the overall structure of the cosmos. I will elucidate the fundamental concepts underlying cosmology, with a specific focus on the Big Bang theory, which serves as the foundation of our understanding of the universe. The Big Bang theory asserts that the universe commenced approximately 13.8 billion years ago from a singular, infinitely dense point known as a singularity. Homogeneity and Isotropy: The universe exhibits uniform composition and structure on a large scale, implying that its properties remain consistent across vast distances. 2. Cosmic Redshift: Edwin Hubble’s observations indicated that galaxies are receding from our perspective, suggesting the universe’s expansion. The redshift of light emitted by distant galaxies serves as pivotal evidence for this expansion. 3. Cosmic Microwave Background Radiation (CMB): Detected as a faint glow permeating the universe, the CMB is a remnant of the hot, dense conditions prevailing shortly after the Big Bang. It provides valuable insights into the universe’s early state. 4. These elements laid the groundwork for the universe’s elemental composition. Galactic evolution encompasses the processes that drive the formation and development of galaxies over cosmic time. Galaxies, substantial celestial systems composed of stars, stellar remnants, gas, dust, and dark matter, traverse various evolutionary stages influenced by gravitational interactions and mergers. The study of galactic formation and evolution illuminates the mechanisms that shape the large-scale structure of the universe. A fundamental aspect of cosmology is the cosmological principle, which asserts the invariance of the laws of physics throughout the universe. This principle implies that the universe exhibits homogeneity and isotropy on large scales, enabling cosmologists to apply local observations to the cosmos as a whole. It provides a framework for comprehending the universe’s structure and the distribution of galaxies across vast distances. Commencing with Earth, we occupy a relatively modest position within the solar system, which comprises the Sun and other celestial bodies. The solar system resides within the Milky Way galaxy, an expansive structure approximately 100,000 light years in diameter, harboring over 200 billion stars. The Milky Way is part of a local galactic group that includes the Andromeda galaxy, which is gravitationally bound to it. Proceeding outward, we encounter the Virgo Supercluster, a vast assemblage of thousands of galaxies spanning approximately 200 million light years. Overall, the segment emphasizes clear definitions, underlying geometry, and practical observing guidance so viewers can connect the concept to the real sky.