Complex sentence: C/1999 F1 (Catalina) is a long-period comet, in fact one of the longest long-period comets, discovered on March 23,1999, by the Catalina Sky Survey.
Split into simpler sentences: C/1999 F1 (Catalina) is one of the longest known long-period comets. It was discovered on March 23,1999, by the Catalina Sky Survey.