The author's excellent 'powers of observation' [=ability to notice and pay close attention to things] are evident in the book's detailed descriptions.
The plants seem to have recovered from the disease, but they are still 'under observation'. [=someone is watching them carefully]
They're keeping him at the hospital 'for observation' [=so that doctors can watch him carefully] for another few days.
(..) There they are. Get them. - - R, locate the chancellor. OBI-WAN: The chancellor’s signal is coming from right there– the observation platform at the top of that spire. I sense Count Dooku. - I sense a trap. - Next move? - Spring the trap. (..)2005 Star Wars: Episode III - Revenge of the Sith