Complex sentence: He was an observer in charge of the International Latitude Observatory, Ukiah, California, in 1898, and from 1899 to 1903 he was astronomer at Yerkes Observatory, where he pioneered the use of photographic methods to determine stellar parallaxes.
Split into simpler sentences: He was an observer in charge of the International Latitude Observatory, Ukiah, California, in 1898. From 1899 to 1903, he was an astronomer at Yerkes, where he pioneered the use of photographic methods to determine stellar parallaxes.