What is the difference between a galaxy and a solar system?

A galaxy and a solar system are both structures in the universe, but they differ significantly in size, composition, and function. Here’s a breakdown of the key differences:

• Size and Scale
  • Galaxy:
    • A galaxy is an enormous system composed of billions of stars, along with their solar systems, gas, dust, and dark matter, all held together by gravity.
    • Example: The Milky Way galaxy, which is about 100,000 light-years across.
  • Solar System:
    • A solar system is much smaller and consists of a single star and the celestial objects bound to it by gravity, such as planets, moons, asteroids, and comets.
    • Example: Our solar system, centered around the Sun, spans about 0.001 light-years (or approximately 100,000 astronomical units).
• Components
  • Galaxy:
    • Contains billions of stars, many of which have their own solar systems.
    • Includes large amounts of interstellar gas and dust.
    • Often has a supermassive black hole at its center (e.g., Sagittarius A* in the Milky Way).
  • Solar System:
    • Consists of one star (like the Sun) and the celestial objects that orbit it:
      • Planets (e.g., Earth, Mars).
      • Moons (e.g., the Moon, Europa).
      • Dwarf planets (e.g., Pluto).
      • Smaller objects like asteroids and comets.
• Gravity and Organization
  • Galaxy:
    • Gravity holds together the vast collection of stars and their systems within the galaxy.
    • Stars orbit the galaxy’s center, where a supermassive black hole or dense star cluster may exist.
  • Solar System:
    • Gravity from the central star (e.g., the Sun) governs the orbits of planets and other celestial objects within the system.
    • Planetary systems revolve around their star, not the galaxy itself.
• Examples
  • Galaxy:
    • The Milky Way (our galaxy).
    • Andromeda Galaxy (M31).
    • Large and Small Magellanic Clouds.
  • Solar System:
    • Our Solar System (Sun, Earth, and other planets).
    • The Alpha Centauri system might have its own planetary system.
• Quantity
  • Galaxy:
    • The observable universe contains an estimated 100–200 billion galaxies.
  • Solar System:
    • A galaxy contains billions of solar systems.