Editing Sundial (section)

{{Short description|Device that tells the time of day by the  apparent position of the Sun in the sky}}
{{Other uses}}
<!--
----PLEASE DO NOT ADD FURTHER IMAGES HERE UNLESS THEY HELP ILLUSTRATE A POINT IN THE TEXT
----THERE ARE ALREADY OVER 1000 IMAGES TO CHOOSE FROM AT COMMONS
----PLEASE UPLOAD YOUR IMAGE TO COMMONS AND IDENTIFY THE LATITUDE AND LONGITUDE OF ITS LOCATION
 -->
[[File:MootHallSundial.JPG|thumb|right|SSW facing, vertical declining sundial on the Moot Hall in [[Aldeburgh]], Suffolk, England. The gnomon is a rod that is very narrow, so it functions as the style. The Latin motto loosely translates as "I only count the sunny hours."]]
[[File:Melbourne sundial at Flagstaff Gardens.JPG|thumb|right|A horizontal dial commissioned in 1862, the gnomon is the triangular blade. The style is its inclined edge.<ref name=VHD>
{{cite VHD|1841|Flagstaff Gardens|hr=2041|ho=793|access-date=2010-09-16 }}
</ref>]]
[[File:AnnMorrisonParkSundial.jpg|thumb|right|A combined [[analemma]]tic-equatorial sundial in Ann Morrison Park in [[Boise, Idaho]], 43°36'45.5"N 116°13'27.6"W]]

A '''sundial''' is a [[horology|horological]] device that tells the time of [[day]] (referred to as [[civil time]] in modern usage) when direct [[sunlight]] shines by the [[position of the Sun|apparent position]] of the [[Sun]] in the [[sky]]. In the narrowest sense of the word, it consists of a flat plate (the ''dial'') and a [[gnomon]], which casts a [[shadow]] onto the dial. As the Sun [[diurnal motion|appears to move]] through the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The ''style'' is the time-telling edge of the gnomon, though a single point or ''nodus'' may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be [[polar alignment|parallel to the axis]] of the [[Earth's rotation]] for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical [[latitude]].

The term ''sundial'' can refer to any device that uses the Sun's [[horizontal coordinate system|altitude]] or [[azimuth]] (or both) to show the time. Sundials are valued as decorative objects, [[metaphor]]s, and objects of intrigue and mathematical study.

The passing of time can be observed by placing a stick in the sand or a nail in a board and placing markers at the edge of a shadow or outlining a shadow at intervals. It is common for inexpensive, mass-produced decorative sundials to have incorrectly aligned gnomons, shadow lengths, and hour-lines, which cannot be adjusted to tell correct time.<ref>{{cite web |last=Moss |first=Tony |title=How do sundials work |url=http://www.sundialsoc.org.uk/HDSW.php |publisher=British Sundial society |access-date=21 September 2013 |quote=This ugly plastic ‘non-dial’ does nothing at all except display the ‘designer’s ignorance and persuade the general public that ‘real’ sundials don’t work. |url-status=dead |archive-url=https://web.archive.org/web/20130802033857/http://www.sundialsoc.org.uk/HDSW.php |archive-date=August 2, 2013}}</ref>

{{TOC limit|3}}