Generations of stargazers and astronomy students learned about the universe from Robert H. Baker. The University of Illinois Observatory director published and revised astronomy textbooks and popular books into his 80s, with revisions by others continuing into the 1970s. His first book, Astronomy: An Introduction, debuted just in time to depict the 1930 discovery of Pluto, called “Trans-Neptunian Planet” in the first edition. It joins the public domain in 45 days. #PublicDomainDayCountdown