A Modern View of the Universe

• Modern View of the Universe
  • Aims to explore our place in the universe, its vastness, and how the study of astronomy has influenced human history.

Learning Goals

• Understand Earth's movement through space.
• Analyze the motion of galaxies within the universe.
• Explore the scale of the universe and humanity’s place in it.
• Discuss how our lifetimes compare to the age of the universe.

Our Cosmic Address

• Earth as a planet in the solar system, which includes the Sun, moons, asteroids, and comets.
• Earth follows its orbit around the Sun within the Milky Way Galaxy, containing more than 100 billion stars.
• The universe comprises billions of galaxies forming groups, clusters, and superclusters.

Astronomical Distance Measurements

• Astronomical Unit (AU):
  • Average distance from Earth to the Sun (~150 million km or ~93 million miles).
• Light-Year (ly):
  • Distance light travels in one year (~10 trillion km or ~6 trillion miles).

The Scale of the Universe

• Historical views placed Earth at the center of the universe; modern understanding situates Earth as an orbiting planet around an ordinary star.
• The Hubble Space Telescope captures extensive views of the universe, demonstrating its vastness through distance and time.

Concept of Time in Astronomy

• Looking Back in Time:
  • Observing distant galaxies is effectively looking back in time due to the speed of light; light from the Andromeda Galaxy takes 2.5 million years to reach Earth.
• Stars like Sirius appear as they were 8 years ago due to light travel time.

Key Definitions

• Star: Glowing gas ball generating heat and light through nuclear fusion.
• Planet: An object in orbit around a star reflecting light.
• Dwarf Planet: Similar to a planet but hasn’t cleared its orbit.
• Galaxy: A collection of billions of stars, orbiting a common center.
• Supercluster: A collection of multiple galaxy clusters.

The Observable Universe

• The universe is approximately 14 billion years old; beyond certain distances, we cannot observe due to light not having reached us yet.
• Observing galaxies billions of light-years away allows us to see them as they were long ago, before the formation of structures seen today.

Motion of Earth in Space

• Earth rotates on its axis (~1000 km/hr), orbits the Sun (~107,000 km/hr), and moves within the galaxy (~800,000 km/hr).
• Earth’s location in the Milky Way ensures complex movements, including movement towards the Andromeda Galaxy (~300,000 km/hr).

Cosmic Recycling

• Elements heavier than hydrogen and helium are created in stars and recycled through dying stars and subsequent formation of new stars and planets in galaxies.
• The process of stellar life cycles reinforces the notion that we are made of “star stuff.”

Understanding Time on a Cosmic Scale

• The history of the universe and Earth can be condensed into a cosmic calendar illustrating significant events from the Big Bang to the rise of human civilization, showing how brief humans' existence is in cosmic terms.

The Expansion of the Universe

• The universe is expanding; more distant galaxies are moving away faster—a phenomenon illustrated through Hubble's Law and expanded metaphorically through a raisin cake analogy.

The Human Adventure of Astronomy

• The history of astronomy reflects our relationship with the universe, impacting civilization from ancient beliefs to modern scientific revolutions.
• Key figures: Copernicus, Galileo, and Newton contributed to our understanding of the universe.

Summary of Key Concepts

• Earth is not central to the universe; it is a small planet in the Milky Way Galaxy.
• Cosmic distances are vast but can be understood through models and comparisons.
• Our understanding of the universe continuously evolves, influenced by new discoveries and technologies.