 Since these objects could be observed visually with the relatively small-aperture refracting telescope (approximately 100 mm, or 4 inches) used by Messier to study the sky, they are among the brightest and thus most attractive astronomical objects (popularly called deep-sky objects) observable from Earth, and are popular targets for visual study and astrophotography available to modern amateur astronomers using larger aperture equipment.In early spring, astronomers sometimes gather for "Messier marathons", when all of the objects can be viewed over a single night.NOTE