Astronomy 103: The Evolving Universe

Astronomy 103: The Evolving Universe Notes

Artist Illustrations and Imagined Scenarios

  • Milky Way Galaxy: An artist's illustration is used to visualize its structure from an external viewpoint.

  • Distance: The Sun is approximately 50,000 light-years away from a star on the far side of the Galaxy.

  • Hypothetical Civilization:

    • Envision a star with an orbiting planet where a civilization develops space travel technology

    • This scenario is set 2 million years ago, during early human use of stone tools.

    • Questions to consider include:

      • When would this civilization become aware of humanity’s existence?

      • Would 2 million years be sufficient time for them to traverse the Galaxy?

      • What alternative methods might exist for mutual awareness between civilizations?

Role and Actions of Astronomers

Scale of the Universe

  • The Universe: Vast in size, necessitating a new measurement system for vast distances.

  • Solar System Overview:

    • Planets in the Solar System: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto are mentioned, with relative sizes noted but with a disclaimer about distance accuracies.

    • Distance Measurements:

      • Questions arising about how far away other stars are and the variability in size and temperature.

      • Proxima Centauri is featured as the nearest star at about 4 light years from the Sun, with discussions on incorporating it into practical distance scenarios, e.g., a bike ride comparison.

  • Light Year as Distance Measurement:

    • Justification for using a temporal unit for distance, e.g., "Chicago is a 2-hour drive from Madison."

    • The speed of light is constant c=300,000extkm/sc = 300,000 ext{ km/s} (or approximately 7imes108extmiles/hour7 imes 10^8 ext{ miles/hour}).

    • Definition of a light-year as the distance light travels in one year: about 1012extkilometers10^{12} ext{ kilometers}.

    • Time taken for light to traverse distances can be described using the formula exttime=racextdistanceextspeedext{time} = rac{ ext{distance}}{ ext{speed}}.

The Structure of Our Galaxy

  • Milky Way Galaxy Features:

    • Contains an estimated over 100 billion stars.

    • Measures about 100,000 light years across.

    • Notable presence of dust clouds that often signify regions of star formation.

    • Approximate distances include:

      • Distance from Earth to the Sun: 8 light minutes

      • Nearest star: 4 light years

      • Nearest galaxies: approximately 3 million light years away, with galaxy clusters at about 50 million light years.

    • Image references from reputable sources emphasize understanding cosmic scales (e.g., dark bands of dust marking star birth sites).

Cluster Structures in the Universe

  • Galaxies do not exist in isolation but are often grouped into larger structures known as clusters and superclusters.

  • Specific images from Hubble, like those of cluster Abell 1689, reference the complex infrastructure of the universe around us.

  • TReading and Homework Assignments

  • Assignments and readings outlined for the first week include:

    • Family of Astronomy: Syllabus and Module 0, including a Syllabus Quiz.

    • Textbook reading assignments for conceptual understanding.

    • Access and usage of Piazza for starter practice assignments.

  • Discussion Sections:

    • Discussions commence on January 21, focusing on foundational math review to facilitate student preparedness for subsequent topics.

This document serves as a comprehensive guide to the introductory lecture for Astronomy 103, capturing key information on course structure, goals, astronomy fundamentals, and success strategies. Students are encouraged to engage actively with the material and utilize available resources for the best experience in the course.