"We were looking at the sky."
Translation:Nosotros estábamos mirando el cielo.
Google translator give Nosotros mirabamos el cielo as translating to We watched the sky.
Nosotros mirábamos el cielo should be correct as well. It translates as either "We used to watch the sky" or "We were watching the sky."
Most likely because it was more of an ongoing state, since we don't have enough context to justify that it wasn't.
Mirar means "to look at" and the preposition "a" is built in to the verb itself.
From my understanding, this sentence must be in the past progressive tense because the imperfect tense (mirábamos or veíamos) means either "we looked / we used to look", and from what I was taught, it can only mean "we were looking" if an event interrupted it. For example, "Mirábamos el cielo cuando, de repente, oí una explosión", "we were looking at the sky when, suddenly, I heard an explosion"