He pulled out a pair of aviator sunglasses from his coat pocket---he'd been wondering where those sunglasses went off to!---and hopped out of the TARDIS, waiting on his companion.
"See, the rotation of Frotito keeps the suns in constant orbit around this section of the planet," he continued on in his best tourist-guide voice. "So no matter where you are in the city you'll always have sunlight. Not bad after dealing with the Library, I think. Too much dark there."