01_lecture

A Modern View of the Universe

Overview

• Title: The Cosmic Perspective Ninth Edition

• Focus on our place in the universe and fundamental cosmic concepts.

Our Place in the Universe

• Universe: Approx. size: 10 km x 100 million light years.

• Local Supercluster: Approx. size: 3x10 km x 3 million light years.

• Local Group: Approx. size: 10 km x 100,000 years.

• Milky Way Galaxy: Contains solar system and Earth; not to scale.

• Solar System: Approx. size: 10 km; Earth: approx. 100 km x 60 AU.

Key Cosmic Definitions

• Star: A large, glowing ball of gas generating light and heat through nuclear fusion.

• Planet: Moderately large object orbiting a star that shines by reflected light; can be rocky, icy, or gaseous.

• Moon (Satellite): An object that orbits a planet; e.g., Ganymede orbits Jupiter.

• Asteroid: Small rocky object orbiting a star; e.g., Eros.

• Comet: Small icy object that orbits a star.

• Solar (Star) System: Consists of a star and the material orbiting it, including planets and moons.

• Nebula: Interstellar cloud of gas and/or dust.

• Galaxy: A vast collection of stars held together by gravity.

• Universe: Sum total of all matter and energy, including all galaxies.

Astronomical Distances

• Astronomical Unit (AU): Average distance between Earth and Sun (150 million km or 93 million miles).

• Light-year (ly): Distance light travels in 1 year; approximately 10 trillion km (6 trillion miles).

Time and Distance Relationship

• Light travels at 300,000 km/second.

  • To Moon: 1 second

  • To Sun: 8 minutes

  • To Sirius: 8 years

  • To Andromeda Galaxy: 2.5 million years

• Observation of Past: The farther we observe, the farther back in time we look.

  • Example: Orion Nebula viewed as it appeared 1500 years ago.

  • Andromeda Galaxy viewed as it appeared 2.5 million years ago.

Cosmic Scale Comparisons

• Solar System Scale: Sun as grapefruit, Earth as a ballpoint 15 meters away.

• Size of Milky Way: Approximately 100 billion stars; much larger than Earth.

• Counting stars: Takes thousands of years to count all in the Milky Way at one per second.

Cosmic Evolution

• Expansion of Universe: Galaxies moving away from each other; began with Big Bang.

• Gravity's Role: Drives matter collapse into galaxies, forming stars and planets.

• Process of star formation and life cycles, ending after fuel depletion.

Sources of Heavier Elements

• Elements like carbon and iron formed during star nuclear fusion processes.

• A small amount created during the Big Bang.

Lifetimes in Cosmic Perspective

• Cosmic Calendar: Compresses the universe's history into 1 year; humans appear late on December 31.

Earth's Movement in Space

• Earth's movements: Rotates daily; orbits Sun annually at high speeds.

• Gravity's effects on solar system: Stars move relative to one another, rarely colliding.

Hubble's Discoveries

• All galaxies outside the Local Group are receding; their speed increases with distance.

• Conclusion: We live in an expanding universe.

Conclusion: Impact of Astronomy on Human History

• Copernican revolution; shifted perspective of Earth’s place in the universe.

• Study of planetary motion influenced Newton's laws, foundational for the industrial revolution.

• Continuous expansion of our cosmic perspective through modern discoveries.