Editing Sundial (section)

==Altitude-based sundials==
[[File:Ottoman Sundial at the Debbane Palace museum.jpg|thumb|Ottoman-style sundial with folded gnomon and a compass. [[Debbane Palace]] museum, Lebanon.]]
Altitude dials measure the height of the Sun in the sky, rather than directly measuring its hour-angle about the Earth's axis. They are not oriented towards [[true north]], but rather towards the Sun and generally held vertically. The Sun's elevation is indicated by the position of a nodus, either the shadow-tip of a gnomon, or a spot of light.

In altitude dials, the time is read from where the nodus falls on a set of hour-curves that vary with the time of year. Many such altitude-dials' construction is calculation-intensive, as also the case with many azimuth dials. But the capuchin dials (described below) are constructed and used graphically.

Altitude dials' disadvantages:

Since the Sun's altitude is the same at times equally spaced about noon (e.g., 9am and 3pm), the user had to know whether it was morning or afternoon. At, say, 3:00 pm, that is not a problem. But when the dial indicates a time 15 minutes from noon, the user likely will not have a way of distinguishing 11:45 from 12:15.

Additionally, altitude dials are less accurate near noon, because the sun's altitude is not changing rapidly then.
 
Many of these dials are portable and simple to use. As is often the case with other sundials, many altitude dials are designed for only one latitude. But the capuchin dial (described below) has a version that's adjustable for latitude.<ref>{{harvp|Mayall|Mayall|1994|p=169}}</ref>

{{harvp|Mayall|Mayall|1994|p=169}} describe the Universal Capuchin sundial.

===Human shadows===
The length of a human shadow (or of any vertical object) can be used to measure the sun's elevation and, thence, the time.<ref>{{harvp|Rohr|1965|p=15}}; {{harvp|Waugh|1973|pp=1–3}}</ref> The [[Venerable Bede]] gave a table for estimating the time from the length of one's shadow in feet, on the assumption that a monk's height is six times the length of his foot. Such shadow lengths will vary with the geographical [[latitude]] and with the time of year. For example, the shadow length at noon is short in summer months, and long in winter months.
 
[[Chaucer]] evokes this method a few times in his ''[[Canterbury Tales]]'', as in his ''Parson's Tale''.{{efn|
[[Chaucer]]: as in his ''Parson's Tale'':
: It was four o'clock according to my guess,
: Since eleven feet, a little more or less,
: my shadow at the time did fall,
: Considering that I myself am six feet tall.
}}

An equivalent type of sundial using a vertical rod of fixed length is known as a ''[[backstaff|backstaff dial]]''.

===Shepherd's dial – timesticks===
{{Main|Shepherd's dial}}
[[File:Tibetan Timestick.jpg|thumb|19th-century Tibetan shepherd's timestick]]

A [[shepherd's dial]] – also known as a ''shepherd's column dial'',<ref name="story of time">{{cite book |last1=Lippincott |first1=Kristen |last2=Eco |first2=U. |author2-link=Umberto Eco |last3=Gombrich |first3=E.H. |year=1999 |title=The Story of Time |place=London, UK |publisher=Merrell Holberton / National Maritime Museum |isbn=1-85894-072-9 |pages=[https://archive.org/details/storyoftime00kris/page/42 42–43] |url=https://archive.org/details/storyoftime00kris |url-access=registration}}</ref><ref name=beginnings>{{cite web |publisher=St.&nbsp;Edmundsbury Borough Council |title=Telling the story of time measurement: The Beginnings |url=http://www.stedmundsbury.gov.uk/sebc/visit/beginnings.cfm |access-date=2008-06-20 |url-status=dead |archive-url=https://web.archive.org/web/20060827151541/http://www.stedmundsbury.gov.uk/sebc/visit/beginnings.cfm |archive-date=August 27, 2006 }}</ref> ''pillar dial'', ''cylinder dial'' or ''chilindre'' – is a portable cylindrical sundial with a knife-like gnomon that juts out perpendicularly.<ref>{{harvp|Rohr|1965|pp=109–111}}; {{harvp|Waugh|1973|pp=150–154}}; {{harvp|Mayall|Mayall|1994|pp=162–166}}</ref> It is normally dangled from a rope or string so the cylinder is vertical. The gnomon can be twisted to be above a month or day indication on the face of the cylinder. This corrects the sundial for the equation of time. The entire sundial is then twisted on its string so that the gnomon aims toward the Sun, while the cylinder remains vertical. The tip of the shadow indicates the time on the cylinder. The hour curves inscribed on the cylinder permit one to read the time. Shepherd's dials are sometimes hollow, so that the gnomon can fold within when not in use.

The shepherd's dial is evoked in ''[[Henry VI, Part 3]]'',{{efn|
[[Henry VI, Part 3]]:
: O God! methinks it were a happy life
: To be no better than a homely swain;
: To sit upon a hill, as I do now,
: To carve out dials, quaintly, point by point,
: Thereby to see the minutes, how they run –
: How many makes the hour full complete,
: How many hours brings about the day,
: How many days will finish up the year,
: How many years a mortal man may live.<ref>
{{cite book
 |author=Shakespeare, W. |author-link=William Shakespeare
 |title=[[Henry VI, Part 3]]
 |at=act&nbsp;2, scene&nbsp;5, lines&nbsp;21–29
}}
</ref>
}}
among other works of literature.{{efn|
For example, in the ''[[Canterbury Tales]]'', the monk says
: "Goth now your wey," quod he, "al stille and softe,
: And lat us dyne as sone as that ye may;
: for by my chilindre it is pryme of day."<ref>
{{cite book
 |author=Chaucer, Geoffrey |author-link=Geoffrey Chaucer
 |year=
 |title=[[Canterbury Tales]]
 |editor=
 |translator=
 |section=   |at= 
 |place=
 |publisher=
 |isbn=
}}
</ref>{{full citation needed |date=June 2023 |reason=Which tale? Which edition? Publisher? Date? Page?}}
}}

The cylindrical shepherd's dial can be unrolled into a flat plate. In one simple version,<ref>{{harvp|Waugh|1973|pp=166–167}}</ref> the front and back of the plate each have three columns, corresponding to pairs of months with roughly the same solar declination (June:July, May:August, April:September, March:October, February:November, and January:December). The top of each column has a hole for inserting the shadow-casting gnomon, a peg. Often only two times are marked on the column below, one for noon and the other for mid-morning / mid-afternoon.

Timesticks, ''clock spear'',<ref name="story of time"/> or ''shepherds' time stick'',<ref name="story of time"/> are based on the same principles as dials.<ref name="story of time"/><ref name=beginnings/> The time stick is carved with eight vertical time scales for a different period of the year, each bearing a time scale calculated according to the relative amount of daylight during the different months of the year. Any reading depends not only on the time of day but also on the latitude and time of year.<ref name=beginnings/>
A peg gnomon is inserted at the top in the appropriate hole or face for the season of the year, and turned to the Sun so that the shadow falls directly down the scale. Its end displays the time.<ref name="story of time"/>

===Ring dials===
In a ring dial (also known as an ''Aquitaine'' or a ''perforated ring dial''), the ring is hung vertically and oriented sideways towards the sun.<ref>{{harvp|Rohr|1965|p=111}}; {{harvp|Waugh|1973|pp=158–160}}; {{harvp|Mayall|Mayall|1994|pp=159–162}}</ref> A beam of light passes through a small hole in the ring and falls on hour-curves that are inscribed on the inside of the ring. To adjust for the equation of time, the hole is usually on a loose ring within the ring so that the hole can be adjusted to reflect the current month.

===Card dials (Capuchin dials)===
Card dials are another form of altitude dial.<ref>{{harvp|Rohr|1965|p=110}}; {{harvp|Waugh|1973|pp=161–165}}; {{harvp|Mayall|Mayall|1994|p=166–185}}</ref> A card is aligned edge-on with the sun and tilted so that a ray of light passes through an aperture onto a specified spot, thus determining the sun's altitude. A weighted string hangs vertically downwards from a hole in the card, and carries a bead or knot. The position of the bead on the hour-lines of the card gives the time. In more sophisticated versions such as the Capuchin dial, there is only one set of hour-lines, i.e., the hour lines do not vary with the seasons. Instead, the position of the hole from which the weighted string hangs is varied according to the season.

The Capuchin sundials are constructed and used graphically, as opposed the direct hour-angle measurements of horizontal or equatorial dials; or the calculated hour angle lines of some altitude and azimuth dials.

In addition to the ordinary Capuchin dial, there is a universal Capuchin dial, adjustable for latitude.

===Navicula===
[[File:Navicula de Venetiis-MHS 2139-P7220157-gradient.jpg|thumb|[[Navicula de Venetiis]] on display at [[Musée d'histoire des sciences de la Ville de Genève]].]]

A [[navicula de Venetiis]] or "little ship of Venice" was an altitude dial used to tell time and which was shaped like a little ship. The cursor (with a plumb line attached) was slid up / down the mast to the correct latitude. The user then sighted the Sun through the pair of sighting holes at either end of the "ship's deck". The plumb line then marked what hour of the day it was.{{citation needed|date=July 2018}}