Editing Sundial (section)

==In the Southern Hemisphere==
[[File:Sundial in Supreme Court Gardens, Perth.jpg|thumb|230px|left|Southern-hemisphere sundial in [[Perth]], [[Australia]]. Magnify to see that the hour marks run anticlockwise. Note graph above the [[gnomon]] of the [[Equation of Time]], needed to correct sundial readings.]]

A sundial at a particular [[Earth#Orbit and rotation|latitude]] in one [[Sphere|hemisphere]] must be reversed for use at the opposite latitude in the other hemisphere.<ref name="C.S.">{{cite web | last =Sabanski | first =Carl | title =The Sundial Primer | url =http://www.mysundial.ca/tsp/north_vs_south.html | access-date =2008-07-11 | archive-date =2008-05-12 | archive-url =https://web.archive.org/web/20080512145205/http://www.mysundial.ca/tsp/north_vs_south.html | url-status =live }}</ref> A vertical direct south sundial in the [[Northern Hemisphere]] becomes a vertical direct north sundial in the [[Southern Hemisphere]]. To position a horizontal sundial correctly, one has to find true [[north]] or [[south]]. The same process can be used to do both.<ref name="S.P.01">{{cite web | first=Michelle B. |last=Larson | title =Making a sundial for the Southern hemisphere 1 | url =http://solar.physics.montana.edu/YPOP/Classroom/Lessons/Sundials/south.html | access-date =2008-07-11 | archive-date =2020-11-13 | archive-url =https://web.archive.org/web/20201113002556/http://solar.physics.montana.edu/YPOP/Classroom/Lessons/Sundials/south.html | url-status =live }}</ref> The gnomon, set to the correct latitude, has to point to the true south in the Southern Hemisphere as in the Northern Hemisphere it has to point to the true north.<ref name="S.P.02">{{cite web | first=Michelle B. |last=Larson | title =Making a sundial for the Southern hemisphere 2 | url =http://solar.physics.montana.edu/cgi-bin/novlesson_S.cgi | access-date =2008-07-11 | archive-date =2021-03-17 | archive-url =https://web.archive.org/web/20210317185414/http://solar.physics.montana.edu/cgi-bin/novlesson_S.cgi | url-status =live }}</ref> The hour numbers also run in opposite directions, so on a horizontal dial they run anticlockwise (US: counterclockwise) rather than clockwise.<ref>{{cite web | publisher =  British Sundial Society | title = The Sundial Register | url =  http://www.sundialsoc.org.uk/glossary/index.htm| archive-url =  https://web.archive.org/web/20091220122230/http://www.sundialsoc.org.uk/glossary/index.htm| url-status =  dead| archive-date =  2009-12-20| access-date = 2014-10-13 }}</ref>

Sundials which are designed to be used with their plates horizontal in one hemisphere can be used with their plates vertical at the complementary latitude in the other hemisphere. For example, the illustrated sundial in [[Perth]], [[Australia]], which is at latitude 32° South, would function properly if it were mounted on a south-facing vertical wall at latitude 58° (i.e. 90° − 32°) North, which is slightly further north than [[Perth, Scotland]]. The surface of the wall in Scotland would be parallel with the horizontal ground in Australia (ignoring the difference of longitude), so the sundial would work identically on both surfaces. Correspondingly, the hour marks, which run counterclockwise on a horizontal sundial in the southern hemisphere, also do so on a vertical sundial in the northern hemisphere. (See the first two illustrations at the top of this article.) On horizontal northern-hemisphere sundials, and on vertical southern-hemisphere ones, the hour marks run clockwise.