Messier 25 is a large, loose, open cluster in Sagittarius. M25 shines at magnitude 4.6, so it can be viewed with the unaided eye under good sky conditions at a dark-sky observing site. It subtends an apparent angle of 25 arcminutes, the same size as the full moon. At a distance of 2,000 light-years, this would correspond to a true size of 16 light-years in diameter in space.