I just (two minutes ago) finished Michael Flynn's Eifelheim ('ei' is pronounced like the vowel in 'ice'). I highly recommend it.
It's not an easy read--it's written at an adult level, and, unless you understand German, Latin, Middle-age history, and physics, there are bound to be things that don't make sense. That's okay. I've decided a good book is a lot like a good president--smarter than me. Meanwhile, just by reading, I become smarter.
Eifelheim is German for "home of the elves". The main storyline occurs in the middle-ages (think plague time). But it's not fantasy.
And the elves aren't elves...they're aliens.
The story had a bit of an emotional impact on me (and books rarely do that, so for that reason alone I'll recommend it).
It also examines how the language of religion and the language of science interact. The aliens don't comprehend religion, and the people don't understand science (although one in particular tries). Remember, during this time period people still thought that the earth was the center of the universe. They explained just about everything with "God did it". That explanation explains nothing (although it may be true). Some people still use it today. Fortunately, however, we now (like these scientific aliens) know what causes disease and malnutrition.
Anyway, a great book. Go and read it. Meanwhile, I'll go back and read some more stuff by Michael Flynn, and hope that it's as good as this.