2a. Introduction to Astronomy

Steven Earle and Karla Panchuk

Learning Objectives

After carefully reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:

  • Describe what happened during the big bang, and explain how we know it happened
  • Explain how clouds of gas floating in space can turn into stars, planets, and solar systems
  • Describe the types of objects that are present in our solar system, and why they exist where they do
  • Outline the early stages in Earth’s history, including how it developed its layered structure, and where its water and atmosphere came from
  • Explain how the Moon formed, and how we know
  • Summarize the progress so far in the hunt for habitable-zone planets outside of our solar system
  • Explain why the planetary systems we have discovered so far raise questions about our model of how the solar system formed


The story of how Earth came to be is a fascinating contradiction. On the one hand, many, many things had to go just right for Earth to turn out the way it did and develop life. On the other hand, the formation of planets similar to Earth is an entirely predictable consequence of the laws of physics, and it seems to have happened more than once.

We will start Earth’s story from the beginning—the very beginning—and learn why generations of stars had to be born and then die explosive deaths before Earth could exist. We will look at what it takes for a star to form, and for objects to form around it, as well as why the nature of those objects depends on how far away from the central star they form.

Earth spent its early years growing up in a very rough neighborhoods, and we will discuss how Earth’s environment influenced its development, including how it got its moon from what was quite literally an Earth-shattering blow. This chapter will also discuss the hunt for Earth-like exoplanets that exist outside of our solar system).

Licenses and Attributions

“Physical Geology – 2nd Edition” by Steven Earle (Chapter 22 is written by Karla Panchuk) is licensed under CC BY 4.0 Adaptation: Renumbering, Remixing





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2a. Introduction to Astronomy Copyright © 2021 by Steven Earle and Karla Panchuk is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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