Fancy buying yourself a nice little Christmas present? Check out the Humble Book Bundle: Astronomy offer:
https://www.humblebundle.com/books/a...my-book-bundle
Choose how much you want to pay, and download yourself a few astronomy ebooks (in ePub or PDF format). The asking price is ridiculously cheap (although you can pay as much as you want!), and some of the proceeds go to charity - the default charity is the Challenger Center for Space Science Education:
http://www.challenger.org/
US$1.00 to US$7.99 will get you 4 ebooks:
A Stargazing Program for Beginners - A Pocket Field Guide
Weird Astronomy - Tales of Unusual, Bizarre, and Other Hard-To-Explain Observations
Racing the Moon's Shadow with Concorde 001
Rock Legends - The Asteroids and Their Discoverers
US$8.00 to US$14.99 will unlock an additional 5 titles, and anything over US$15.00 will give you a total of 13 astronomy-related titles.
Well worth a look!