marking the location of bright and more challenging deep-sky objects There are many amateur astronomical techniques and activities associated with deep-sky objects. Some of these objects are bright enough to find and see in binoculars and small telescopes. But the faintest objects need the
light-gathering power of telescopes with large
objectives, and since they are invisible to the naked eye, can be hard to find. This has led to increased popularity of
GoTo telescopes that can find DSOs automatically, and large
reflecting telescopes, such as
Dobsonian style telescopes, with wide fields of view well suited to such observing. Observing faint objects needs dark skies, so these relatively portable types of telescopes also lend themselves to the majority of amateurs who need to travel outside
light polluted urban locations. To cut down light pollution and enhance contrast, observers employ
nebular filters, which are designed to admit certain wavelengths of light and block others. There are organized activities associated with DSOs such as the
Messier marathon, which occurs at a specific time each year and involves observers trying to spot all 110 Messier objects in one night. Since the Messier catalog objects were discovered with relatively small 18th-century telescopes, it is a popular list with observers, being well within the grasp of most modern amateur telescopes. The
Herschel 400 Catalogue is also a popular list with observers and is considered more challenging; it was designed for larger
telescopes and experienced amateur astronomers. ==List of deep-sky object types==