Planets, Stars, Galaxies, and the Universe



About Lesson 9

Our view of the Earth's place in the universe has been evolving during this course. Originally, we considered the view of the night sky from a location on Earth. Our observations from the Earth can lead to the biased view that the Earth is the center of the universe, and in fact, this was the dominant theory for centuries. Careful observations and related advances in the theories created to explain these observations led to the revolutionary proposal that the Earth is really just one planet in orbit around the Sun. Subsequent studies of the stars and gas in the Milky Way have now established that the Sun is just one of many billions of stars located in the outskirts of the disk of the Galaxy.

In this lesson, we are going to continue to expand our understanding of the Earth's location in the universe. This time, we are going to place the Milky Way in context by studying the number and distribution of other galaxies like our own, as well as the variety of galaxies that are unlike our Milky Way.

What will we learn in Lesson 9?

By the end of Lesson 9, you should be able to:

  • Compare and contrast the other galaxies in the Universe using the traditional tuning fork model;
  • Qualitatively describe the process by which galaxies evolve;
  • Compare and contrast a normal galaxy and an active galaxy;
  • Describe the spatial distribution of galaxies within the Universe and the environments in which galaxies reside.

What is due for Lesson 9?

Lesson 9 will take us one week to complete.

Please refer to the Calendar in Canvas for specific time frames and due dates.

There are a number of required activities in this lesson. The chart below provides an overview of those activities that must be submitted for Lesson 9. For assignment details, refer to the lesson page noted.

Lesson 9 Requirements
Requirement Submitting your work
Lesson 9 Quiz Your score on this quiz will count towards your overall quiz average.
Unit 3 Lab, Part 1 During Lesson 9, you will begin work on the Galaxies lab listed under Lab 3, Part 1.


If you have any questions, please post them to the General Questions and Discussion forum (not email). I will check that discussion forum daily to respond. While you are there, feel free to post your own responses if you, too, are able to help out a classmate.