Editing Deep-sky object (section)

==Observations and activities==
[[File:CygnusOBmap.png|thumb|right|250px|Map of the constellation [[Cygnus (constellation)|Cygnus]] 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 [[Optical telescope#Light-gathering power|light-gathering power]] of telescopes with large [[Objective (optics)|objectives]],<ref>{{cite book|author1=Grant Privett|author2=Paul Parsons|title=The Deep-Sky Observer's Year: A Guide to Observing Deep-Sky Objects Throughout the Year|url=https://books.google.com/books?id=wWdvYeDbf8gC&pg=PA12|year=2001|publisher=Springer Science & Business Media|isbn=978-1-85233-273-0|page=11}}</ref> and since they are invisible to the naked eye, can be hard to find. This has led to increased popularity of [[GoTo (telescopes)|GoTo telescopes]] that can find DSOs automatically, and large [[reflecting telescope]]s, such as [[Dobsonian]] style telescopes, with wide fields of view well suited to such observing.<ref>{{cite book|author=Rajiv Gupta|title=Observer's Handbook 2005|url=https://books.google.com/books?id=HKMKjfKNzE4C|date=September 2004|publisher=Royal Astronomical Soc of Canada|isbn=978-0-9689141-8-2|page=73}}</ref> 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 pollution|light polluted]] urban locations.<ref>''The Observer's Handbook'', Royal Astronomical Society of Canada, p. 63</ref> To cut down light pollution and enhance contrast, observers employ [[Astronomical filter#Nebular filters|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.<ref>{{cite book |title=The Amateur Astronomer's Guide to the Deep-Sky Catalogs |first=Jerry D. |last=Cavin |date=2011 |publisher=Springer New York |isbn=9781461406563 |page=149 |url=https://books.google.com/books?id=obLAoHOVodAC&pg=PA149}}</ref>