Why is the chapter called "Twinkle Twinkle little Star"?

In chapter 5 of Whirligig, Brent's on his way to San Diego after having had a pretty unpleasant time of it in San Francisco. The experience hasn't been a dead loss, however, as he's bought himself a very interesting book on astronomy. While sitting on the bus, Brent compares the stars in the book with the constellations he sees twinkling in the night sky above. The stars even have names—he previously didn't know that—and exotic names too like Deneb, in the constellation Cygnus. Brent particularly likes Vega, a bluish white star that seems to be staring right at him.
Later on in the chapter, when Brent's staying at a hostel in San Diego, he gets out his harmonica at regular intervals and starts playing tunes like "Hot Cross Buns," "Tom Dooley," and "Twinkle twinkle little star."