Essential Concepts in Astrophysics and Cosmology

Fundamental Astronomical Concepts

Planetary Models

• Geocentric System: A global model that claims Earth is the center of the universe, around which the sun and other planets revolve.
• Heliocentric System: A planetary model that assumes the sun is the center of our system, around which other planets, including Earth, revolve.

Astrophysics and Cosmology

• Astrophysics: The branch of astronomy that studies the structure, composition, and evolution of stars.
• Cosmology: The branch of astronomy that studies the structure, origin, and evolution of the universe.

Space and Time

• Light-Year: The distance light travels in one year in a vacuum at a velocity of 300,000 km/s, approximately 9.5 trillion km.
• Big Bang Theory: A model that explains the formation of the universe from the expansion of a point that contained all energy. This expansion created the space of the universe, and from the energy contained, particles were generated to form matter.

Galaxies and Stars

• Galaxies: Clusters of billions of stars rotating around a common axis, typically elliptical, spiral, or irregular in shape.
• Milky Way: The spiral galaxy where Earth is located.
• Stars: Celestial bodies composed mainly of hydrogen atoms that merge to produce helium, emitting light and heat.
• Supernova: The final state of a star greater than 1.5 times the mass of the sun, resulting in a massive explosion.
• Black Hole: The final state of a star with a mass at least three times that of the sun; its gravitational pull is so great that not even light can escape.

Physics of Motion and Gravity

• Planet: A celestial object without its own light that revolves around a star, often accompanied by satellites.
• Universal Law of Gravitation: Two bodies attract each other with a force directly proportional to the product of their masses and inversely proportional to the square of the distance separating them.
• Gravitational Centripetal Force: A central force caused by gravitational interaction that causes bodies to orbit one another.
• Weight: The force with which a planet or stellar object attracts a body.
• Gravity: The acceleration of a freely falling body, which depends on the mass and radius of the attracting planet.