Well it appeared that he did not know the planet Trenzalore. But that was probably because it does not existed outside of fiction. Nigel shrugs then answers.

"Trenzalore is a planet that has a battlefield graveyard and the tomb of the Doctor. Also no living creature can speak falsely or fail to answer, while on the planet. Though inside the tomb was not a body, but an entity that contained the Doctor's personal time tunnel from Gallifrey to Trenzalore."

Well that is enough about Trenzalore. So know back to his question about constellations."There is the Corona Borealis". Though Nigel was not sure if that was visible in December.