Harry turned and walked over to the spiral pattern drawn in runes and inlaid with jewels on the stones of the Tower, open to the sky. The jewels flashed in patterns that corresponded to several of the constellations overhead. Harry had wondered at first where they would get so many jewels, but it turned out that there were lots of purebloods at the school who had that kind of thing, and Hermione and her handy Imperius Curse meant they were eager to donate.