📓 Our Universe: Introduction to the solar system, stars, and galaxies

Introduction to the Solar System

1. Definition: The solar system consists of the Sun and the objects that orbit it, including planets, dwarf planets, asteroids, comets, and other smaller bodies.
2. Components:
    1. Sun (star at the center)
    2. Eight planets (Mercury to Neptune)
    3. Dwarf planets (Pluto, Eris, etc.)
    4. Asteroids (small rocky objects)
    5. Comets (icy bodies that release gas and dust)
3. Formation: The solar system formed approximately 4.6 billion years ago from a giant cloud of gas and dust called the solar nebula.

Stars
1. Definition: Stars are massive, luminous balls of gas that are held together by their own gravity.
2. Life Cycle:
    1. Protostar (formation)
    2. Main Sequence (stable, fusing hydrogen into helium)
    3. Red Giant (expanding, cooling)
    4. White Dwarf (contracting, cooling)
    5. Supernova (explosion)
    6. Neutron Star or Black Hole (remnant)
3. Types:
    1. Main Sequence stars (like the Sun)
    2. Red Giants
    3. Blue Giants
    4. Neutron Stars
    5. Black Holes

Galaxies
1. Definition: Galaxies are massive, gravitationally bound systems consisting of stars, stellar remnants, interstellar gas, dust, and dark matter.
2. Types:
    1. Spiral Galaxies (like the Milky Way)
    2. Elliptical Galaxies
    3. Irregular Galaxies
3. Components:
    1. Stars
    2. Interstellar Medium (gas and dust)
    3. Dark Matter
    4. Black Hole (at the center)

Key Concepts

1. Big Bang Theory: The universe began as an infinitely hot and dense point and expanded rapidly around 13.8 billion years ago.
2. Cosmology: The study of the origin, evolution, and fate of the universe.
3. Astronomy: The study of celestial objects, space, and the universe.

Examples and Applications
1. Space Exploration: Understanding the solar system, stars, and galaxies informs space missions and the search for extraterrestrial life.
2. Astrophysics: Studying the universe helps us understand fundamental physical laws and processes.
3. Cosmological Research: Investigating the universe's origins and evolution helps us better comprehend our place within it.