Half an hour later, each of them had been given a complicated circular chart,...

Half an hour later, each of them had been given a complicated circular chart, and was attempting to fill in the position of the planets at their moment of birth. It was dull work, requiring much consultation of timetables and calculation of angles.
"I've got two Neptunes here," said Harry after a while, frowning down at his piece of parchment, "that can't be right, can it?"
"Aaaaah," said Ron, imitating Professor Trelawney's mystical whisper, "when two Neptunes appear in the sky, it is a sure sign that a midget in glasses is being born, Harry . . .