sentences:  It was part of the explosion of science fiction magazine publishing in the 1950s in the United States, and was moderately successful, outlasting almost all of its competitors.The main editors were Leo Margulies (1954–1956) and Hans Stefan Santesson (1956–1960); under Santesson's tenure the quality declined somewhat, and the magazine became known for printing much UFO-related material.A collection of stories from the magazine, edited by Santesson, appeared in 1960 from Prentice-Hall, titled "The Fantastic Universe Omnibus".