Do you ever wonder why some fantastic deep-sky targets, like the Crescent Nebula (NGC 6888) in Cygnus and Hyades Cluster in Taurus, aren’t on the list of non-cometary objects Charles Messier put together in 1771? How can the list of 109 celestial wonders seem so incomplete? Sir Patrick Moore questioned the same thing back in 1995, so he set out to add a complementary catalog of an additional 109 targets to round out Messier’s famous list. The result? “The Caldwell Catalog: 109 Deep-Sky Delights for Backyard Observers.”Astronomy magazine subscribers can read the full article for free. Just make sure you're registered with the website.