Intermediate Level Astronomy Textbooks?

[J1998]

Hi all:

I am looking for an astronomy textbook that is a bit above the level of most textbooks used in intro level astronomy courses but also not too advanced.

I would really like a book that focuses on observational astronomy.

If its available to be downloaded for free as a PDF that would be even better.

Thank you

 

[jedishrfu]

there's a free one at Openstax.org which looks to be a comprehensive introduction to Astronomy.

https://openstax.org/books/astronomy/pages/preface

 

[Keith_McClary]

Also #90 here:
https://www.physicsforums.com/threads/free-springer-books-during-lockdown.988144
(and maybe more)