Complex sentence: In 1998, published observations of Type Ia supernovae ("one-A") by the High-Z Supernova Search Team followed in 1999 by the Supernova Cosmology Project suggested that the expansion of the universe is accelerating.
Split into simpler sentences: In 1998, the High-Z Supernova Search Team published observations of Type Ia ("one-A") supernovae. In 1999 by the Supernova Cosmology Project followed by suggested that the expansion of the universe is accelerating.