Learn Spanish (Latin America): Anoche soñé con un planeta deshabitado. - Last night I dreamed of an uninhabited planet.

In Spanish, the verb soñar (to dream) is always paired with the preposition con to express what you dreamed about or dreamed of. It translates literally as "I dreamed with," but it is just a set combination you have to memorize.

Why is it un planeta? Doesn't the -a ending make it feminine?

Planeta is a classic exception to the gender rules. Many Spanish words of Greek origin ending in -ma, -pa, or -ta are masculine. Just like el problema and el mapa, it is always el planeta (or un planeta).

Soñar is a stem-changing verb (yo sueño). Why isn't there a stem change in soñé?

Verbs ending in -ar and -er that have a stem change in the present tense (like the o-to-ue shift in soñar) do not have a stem change in the preterite tense. They conjugate like completely regular verbs, which is why it is soñé and not sueñé.

How would I change this sentence to say "I had been dreaming about a planet for hours" using the hacía... que structure?