Moon of Vega

The Moon of Vega was a moon located 4.2 million light years away from Earth. While visiting there, the Eleventh Doctor projected a hologram of himself from his TARDIS to the home of Nora Wicker, who was stuck in a Time Bubble of the Doctor's creation and needed his help understanding why. (AUDIO: The World Tree)

Behind the scenes
Writer Nick Slawicz confirmed that the Moon of Vega's name was an intentional reference to the location of the same name in the 1987 parody sci-fi film Spaceballs.