Editing Triangulum Galaxy (section)

==Visibility==
Under exceptionally good viewing conditions with no [[light pollution]], the Triangulum Galaxy can be seen by some people with the fully dark-adapted [[naked eye]];<ref name=bort/> to those viewers, it is the farthest permanent entity visible without magnification, being about half again as distant as Messier 31, the Andromeda Galaxy.<ref name=naeye08/><ref name=skiff97/> It is a diffuse, or extended, object rather than a starlike point, even without magnification, because of its physical extent.

Its observability without optical aid ranges from being relatively easily seen by people using direct vision in deep rural locations under a dark, clear, transparent sky, to requiring use of [[averted vision]] by observers in locations beyond the suburbs in shallow rural areas under good viewing conditions.<ref name=bort/> It is one of the reference objects of the [[Bortle Dark-Sky Scale]].

[[Andrew Crumey|Crumey]] has shown that although the total apparent V-magnitude of M33 is 5.72, it has an effective visual magnitude of approximately 6.6, meaning that a precondition for visibility is that the observer can see stars at least as faint as that latter figure.<ref>{{Cite journal |last=Crumey |first=Andrew |author-link=Andrew Crumey |date=11 August 2014 |title=Human contrast threshold and astronomical visibility |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=442 |issue=3 |pages=2600–2619 |arxiv=1405.4209 |bibcode=2014MNRAS.442.2600C |doi=10.1093/mnras/stu992 |issn=1365-2966 |doi-access=free}}</ref> This is fainter than many people are able to see, even at a very dark site.<ref>{{Cite journal |last=Weaver |first=Harold F. |date=October 1947 |title=The Visibility of Stars Without Optical Aid |journal=[[Publications of the Astronomical Society of the Pacific]] |volume=59 |issue=350 |pages=232 |bibcode=1947PASP...59..232W |doi=10.1086/125956 |issn=0004-6280 |s2cid=51963530 }}</ref>