Complex sentence: For the next three years, he was a postdoctoral research associate at Princeton University, and in 1994, he joined the Hayden Planetarium as a staff scientist and the Princeton faculty as a visiting research scientist and lecturer.
Split into simpler sentences: For the next three years, he was a postdoctoral research associate at Princeton University. In 1994 he joined the Hayden Planetarium as a staff scientist and the Princeton faculty as a visiting research scientist and lecturer.