Editing Angular diameter (section)

{{Short description|How large a sphere or circle appears}}
{{More citations needed|date=September 2009}}
[[File:Angular diameter.jpg|thumb|300px|Angular diameter: the angle subtended by an object]]

The '''angular diameter''', '''angular size''', '''apparent diameter''', or '''apparent size''' is an [[angular separation]] (in [[units of angle]]) describing how large a [[sphere]] or [[circle]] appears from a given point of view. In the [[vision sciences]], it is called the ''[[visual angle]]'', and in [[optics]], it is the ''[[angular aperture]]'' (of a [[lens (optics)|lens]]). The angular diameter can alternatively be thought of as the [[angular displacement]] through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side.

A person can [[Angular resolution|resolve]] with their [[naked eye]]s diameters down to about 1&nbsp;[[arcminute]] (approximately 0.017° or 0.0003 radians).<ref name="Yanoff2009">{{cite book |  title=Ophthalmology 3rd Edition  | author1-first=Myron | author1-last=Yanoff | author2-first=Jay S. | author2-last=Duker | publisher=MOSBY Elsevier | year=2009 | isbn=978-0444511416 | page=54 | url=https://books.google.com/books?id=u43MTFr7-m8C&pg=PA54 }}</ref> This corresponds to 0.3&nbsp;m at a 1&nbsp;km distance, or to perceiving [[Venus]] as a disk under optimal conditions.