Today's free book is
Star-Names and Their Meanings by Richard Hinckley Allen. For the table of contents, check at the bottom of this post below the image. The book is something like a dictionary or encyclopedia of star names, so make sure to use the index at the end of the book if you are looking for a particular star!
The book is available at
Internet Archive,
Hathi Trust, and
Google Books.
Solar Zodiac
Lunar Zodiac
Constellations
The Galaxy