The Sims 2/Hobbies/Knowledge

Knowledge objects primarily help Sims build their Logic skill, as well as other skills from studying from books.

All bookcases have the same interactions, except more expensive bookcases improve the Environment score. Sims can read books for Fun, but they can also use the Study interaction to improve their Cooking, Mechanical and Cleaning skills. Sims can also read to toddlers and children, which increases Fun for both the toddler/child and the reader. The reader has to be a teen or older. Another interaction with bookcases is the ability to Write in Diary, which satisfies Fun and Comfort. The Sim will sit on the floor and procure a diary, which they'll write in.

Astrowonder Telescope
There are two interactions with telescopes: Look Through and Stargaze. Look Through is only available during the day, while Stargaze is only available at night. Both interactions satisfies Fun and builds the Logic skill, but they are slightly different.

With the Look Through interaction, Sims spy on their neighbours. There is a chance that one of your Sim's neighbours will come over and chew out your Sim.

The other interaction, Stargaze, is the same, but done at night.

Farstar e3 Telescope
This is essentially the same as the cheaper telescope, except the Stargaze interaction brings the chance of your Sim getting abducted by aliens, but the chances of this happening are slim.