This seems to be a clear and comprehensive course.

One does not have to register.
The link below takes you to the Preface page.
Click on the down arrow to the right of the word CONTENTS to see the list of chapters.
Click on the + to the right of a chosen chapter to see a drop-down list of the chaper sections.
Click on the section you wish to read.

 

The link to the course

 

 

The address of this page is

http://sonicpathfinder.org/U3A/Cosmology/Astronomy.html