The great DEBATE

Mount Wilson research fellow Harlow Shapley, a 34-year-old journalist-turned-astronomer, must have been nervous when he climbed the stage in the Baird Auditorium of the Smithsonian Museum of Natural History in Washington, DC; facing him was a crowd of fellow scientists and lay people alike. On stage after him would be his opponent in the debate, eminent astronomer Heber Curtis - a man 13 years his senior, more experienced and eloquent at speaking, and who disagreed with Shapley on just about everything. The two scientists were there to argue the scale of the Universe and whether ‘spiral nebulae’ (what we now know as spiral galaxies) were small and nearby, or huge and far away. On Monday 26 April 1920 at 8.15pm, the historic ‘Great Debate’ began.

One year after the event, Shapley and Curtis presented their conflicting views in the . In a sense, the Great Debate was thus first published in May 1921, exactly a century ago this month. But not many people know that