Complex sentence: He predicted in 1831 that the world would end in 1843; during the 1830s, many comets were seen, including the return of Halley's Comet in 1835.
Split into simpler sentences: He predicted in 1831 that the world would end in 1843. During the 1830s, many comets were seen, including the return of Halley's Comet in 1835.