Contemplation is long, hard thinking about something. If you’re writing a book on the meaning of the universe, then you’re going to need to do a great deal of contemplation.
Contemplate has the word temple in its roots, and originally referred to the kind of thinking you do in a special space set aside for observation. Now we use it to describe any kind of thinking that we spend a long time doing. While clicking on someone’s photos on Facebook doesn’t count as contemplation, usually, you might spend hours in contemplation of your family and your history if you come across a box of old photos in the attic.