Types and Terms
This is not a finite list but should provide a reasonable basis as a starting point on the topic of sundials.
In time examples of each will be referred to either within this blog or via links to invaluable sources of information e.g. organisations such as NASS (the North American Sundial Society) or the BCS (British Sundial Society).
[Please email any corrections to stronsy@gmail.com]
NOTE
Use the built in Google Translate at the top right of this blog to see the content of in a language of your choice. This blog is best viewed with Google Chrome.
Adjustable Sundial
Simply any sundial type that is adjustable.
Adjustable Sundial Alarms
See under Alarm
Sundials.
Alarm Sundials
Sundials that are designed to provide some form of alarm as a result
of the sun reaching a particular point.
The mechanisms for this are many and as imaginative as can
be and today may include electronic devices that emit light, sound or vibration
etc. at the appointed time.
The NASS conference of 2003 reported on these ingenious machines ranging from an elegantly built noon
cannon to other much more fanciful devices that announce the sun’s arrival at
the meridian or other appointed time with a bang from a small firecracker).
Paul Nibley, who builds them, hopes to make several more of
his “industrial model” and his “butterfly model,” complete with solar cells
that powers a chime when the wings of the creature opens.
Altitude
The altitude of the Sun is the vertical angle it makes above
the horizon (from -90° to +90°). The Sun's altitude and azimuth define its
position at any given moment. At sunrise the altitude of the Sun is 0°.
Altitude Sundial
This uses the altitude of the sun at a given latitude and
time of year as a means of telling the time.
Apparent Solar Time
See: Equation of time.
Azimuth
A horizontal angle measured from the meridian. It is
positive towards the East and negative towards the West. The Sun's azimuth at a
particular time is its bearing at that moment. The azimuth is 0° when it
crosses the meridian of a place.
Analemma
If you look at the sun at exactly the same time every day
you will notice the sun is not always in the same place. If you measure the
sun’s location every day during a year, you will see the sun draws an analemma
in the sky (a figure of 8).
This apparent motion of the sun is the result of two motions
of the earth.
Let us assume that the orbit of the earth around the sun is
an exact circle and let us assume that the angle of the axle of the earth is
exactly perpendicular to the plane, in which the earth’s orbit is located.
In that case the sun will be exact at the same point in the
sky at a fixed point in time.
However, the orbit of the earth is an ellipse and the axle
of the earth with its plane of motion is approximately 23.5 degrees. Because of
this, the sun makes its figure of 8-shape in the sky – the analemma.
Analemmatic Sundials
A type of horizontal
sundial
with a vertical
gnomon
and hour markers positioned in an elliptical pattern.
There are no hour lines on the dial and the time of day is
read on the ellipse. The gnomon is not fixed and must change position daily to
accurately indicate time of day.
This may include people acting as the gnomon in which case
they are known as
Human Gnomon.
In Biarritz, France,
there are two analemmatic sundials in marvelous locations
overlooking the great sweep of the bay with its Atlantic waves. These sundials
are especially popular with children; you stand on a spot marked for the month
of the year, and your shadow indicates the approximate time.
Modern Sunclocks of Kilwinning, Ayrshire advise these are
essentially both "theft-proof" and "damage-proof", they are
perfect for public spaces (children's play areas, etc) and are popular as Millennium-markers.
Made from almost any material (stone, wood, concrete,
mosaic) or just painted onto the ground, which is the method normally used by
Junior Schools. Set into a lawn, it
will not interfere with grass-cutting.
They automatically cater for both standard and daylight- saving time - so you never need to adjust your layout.
You can have a maintenance-free conversation piece that is unique - no two
'Sunclocks' are identical, as each layout is specific to its own latitude and longitude. All you need is any level
area around 6 metres (20 feet) across.
Armillary Dials
Armillary dials are equatorial dials with extra circles
emulating those found on armillary spheres. A true armillary sphere is not a
sundial but a model of the heavens. The extra circles on an armillary dial actually hinder
time keeping by blocking the sun at various times.
Original source [September 2008]:
http://www.sundials.org/faq/
Co-latitude
The complementary angle of the latitude of a place, equal to
90° latitude.
Colored/Coloured Light Sundial
Originating from the Light
Sundial idea but utilising coloured filters to provide coloration to the
area around the shadow or to the area around the dial itself. By design this could be variable either
mechanically or naturally based on the time.
For example the filter could be a different colour in the morning to
that in the afternoon.
Cylinder Dials
Also known as the Pillar
Dial or Pyrenean Shepherd’s Dial or Cylinder
Dial.
Not particularly accurate but easy to make and inexpensive
indicating the time from the Sun's altitude, which depends not only on the time
of day, but also on the latitude and time of year.
It is designed for the specific latitude and adjustable for
the date and made from a cylinder, usually hollow, capped by a movable top to
which a gnomon is attached (stored inside when not in use).
Hour lines are either inscribed on the surface or drawn on a
paper glued to the cylinder.
Hour lines appear as curves on the rounded face of the
cylinder and the months of the year are traced around the base of the cylinder.
Declination
of a wall: the
angle which a vertical wall makes relative to the meridian. When one designs a
vertical sundial, one must take account of the declination of the surface on
which it will be placed. In Europe, the
declination of a south-facing wall is 0° of an east-facing wall is -90° of a
wall facing west +90° and one facing north is 180°.
of the Sun: the
position of the Sun north or south of the celestial equator.
Declining Dial
A vertical dial that does not face one of the cardinal
points of the compass (see also: Direct
Dial).
Dial Plate
The supporting surface of a horizontal dial. The lines and
numbers of a dial are laid out on the dial plate.
Dialist
An artisan who designs, constructs and installs sundials.
Diptych dial
A diptych is any object with two flat plates attached at a
hinge and devices of this type were popular in the ancient world. The diptych dial was a portable sundial. A
face was on the inside of each leaf. One leaf formed a vertical sundial, the
other a horizontal sundial. The shadow caster, or gnomon was a string between
them, and calibrated as to how far they should open, as the angle is critical.
Such a sundial can be adjusted to any latitude by tilting it so its gnomon is
parallel to the Earth's axis of rotation.
Direct Dial
A vertical dial that faces one of the cardinal points of the
compass (see also: Declining Dial).
Sundials around the world each with a webcam whose images
will then be linked to a central website so, almost in real time, these
sundials in all the different time zones can be seen.
Check the first web site below for all the details on how
to participate. The basic idea is for schools and individuals around the world
each to build a sundial and set up a webcam that looks at it.
These webcam
images are all linked to a central website in almost real time, you can see sundials from around the world in all the different
time zones!
As your eye sweeps across the images on this web page, the sun's
shadow will be seen to sweep across the faces of the dials. Website viewers
can gain a palpable sense of how the sun illuminates the globe of the Earth.
This project is an adjunct to the first extraterrestrial sundial, the MarsDial
on NASA's Mars Exploration Rovers that landed in January
2004 (see under: MarsDial).
Of course at any given time, half the dials will be in
darkness. Some will be in the Southern Hemisphere where the sun goes through
the northern sky daily, and the hour lines on sundials go in the opposite sense
(anticlockwise). The shapes of the lines on dials in the tropics will contrast
greatly with those in Scandinavia. There will
be a multitude of languages and cultural motifs on the various dials.
Ecliptic
The plane
containing the orbit of the Earth around the Sun, which by extension projects a
circle on the celestial sphere.
Equation of Time
The value of the
difference between Apparent Solar Time
and Mean Solar Time. The difference
arises from the movement of the Earth in its elliptical orbit as well as the
fact that its axis of rotation is inclined to the ecliptic. The difference can
vary by as much as +/- 16 minutes. The Equation of Time is sometimes
represented in the form of a figure of eight placed on the noon line of a
sundial.
Equatorial Dials
See: Equinoctial Sundial.
Equinoctial line
The line of declination on a sundial corresponding to the
equinox. This line makes a right angle with the gnomon in a plane sundial.
Equinoctial Sundial
A type of sundial in which the plane of the shadow-receiving surface is parallel to the equator.
The
equinoctial sundial is also known as equatorial dial because the dial plate rests on a plane parallel with the Earth’s equator.
When set-up properly the dial plate sits on a ring parallel to the equator and the gnomon, sometimes called a polestyle on an equatorial dial, points along a line parallel to the Earth’s axis. Weather permitting a shadow is cast by the gnomon onto the chapters that are engraved in five-minute increments.
 |
| Equinoctial dial |
The
KALA Pocket Sundial for example is based on the universal equinoctial ring sundial, a historic sundial used by ancient sailors and mathematicians. This particular type of sundial also indicates the true North and is aligned with the axis of the Earth. In this case it is designed as a contemporary response to a historic timepiece and can also be used as sun compass, a model of the world or even a piece of jewelry.
Equinox:
The day of the year when the Sun crosses the celestial
equator in its apparent movement. At this moment, the Sun rises exactly in the
East and sets exactly in the West. It is the period of the year when night and
day are of equal length. The equinox occurs on 20 March and 23 September.
Glass Sundials
Not actually sundials themselves but pictures of all types
of sundial that have been categorised on a dedicated website into four
different groups: stained glass, etched glass and plastic, projection, and
mosaic.
Gnomon
Also known as polestyle on an equatorial dial.
An object that by the position or length of its shadow
serves as an indicator especially of the hour of the day. The name given to a style placed vertically
to the plane of a sundial. The shadow cast by the tip of the gnomon can
indicate both the time and the date.
Gnomonics
The science of sundials.
Gnomonist
An amateur sundial enthusiast.
Hand Carved and Monumental Sundials
As far as John Carmichael knows, he is the only professional stone sundial maker in the United States. Unfortunately, with the perfection of mechanical clocks, sundial design and construction have nearly become a lost art and science.
The gallery for his Sundial Sculptures of Tucson Arizona shows just some of the exquisite
hand-carved stone sundials with inlayed brass, beautiful artwork, and multiple
scientific functions.
Unique copyrighted brass cable gnomon is held taught by
heavy counterweight. These precise timekeeping instruments are available in
25" and 40" diameter sizes and larger.
Also design large monumental public sundials. All sundials
are custom-made to order, using the latitude and longitude of the sundial's
location and each customer's particular tastes and requirements (sundial type,
shape, size, artwork, etc.) and includes very informative Sundial Owner's
Manual included.
Sundial Sculptures have a broad range of examples of such works.
Heliochronometers
These give a direct and accurate reading of Standard Time
throughout the sunlit year. It is a precision timepiece determining time
exactly - literally to the minute.
H
eliochronometers, long considered the acme of
sundials, a heliochronometer is an instrument truly worthy of the Millennium.
It is only the heliochronometer that gives a direct and accurate reading of
Standard Time throughout the sunlit year. It is a precision timepiece
determining time exactly - literally to the minute.
Used earlier this century
to set the time of civic clocks and to standardise time on railway networks, it
essentially became redundant, in 1913, with the introduction of Radio Time
Signals.
Original source: Gunning Sundials, England [September 2008].
Horizontal Dials
A type of sundial in which the
plane of the shadow-receiving surface is horizontal.
Hour
Babylonian Hours:
an ancient system which divides the day into 24 hours, commencing at sunrise.
They thus measure the number of hours elapsed since sunrise.
Italian Hours: an
ancient system which divides the day into 24 hours, commencing at sunset. They thus
measure the time left until sunset.
Standard Time:
the time shown by clocks, which will be the same for all inhabitants of a
particular time zone. It is Mean Solar
Time corrected for the difference in longitude between a place and the
reference longitude of the time zone in which it is located.
Mean Solar Time:
Obtained by adding the Equation of Time to the Apparent Solar Time. The Mean
Solar Time gives a constant hour duration over the year. It varies with the
location.
Apparent Solar Time:
the time naturally shown by a sundial. It is defined as 1/24th of the interval
between two successive passages of the Sun across the meridian. This period of
time varies throughout the year.
Temporary Hour:
an ancient system dividing the interval between sunrise and sunset into 12
hours. The length of an hour therefore varied throughout the year! (between
40-80 minutes). These hours are sometimes referred to as Biblical Hours.
Human Gnomon
See under Analemmatic Sundials.
Latitude
The angle formed between the vertical of a place and the
plane of the equator. Northern latitudes are positive; southern latitudes are
negative.
Light Sundial
See under: Renaissance
sundial.
Lines
Hour Lines: lines
drawn on the dial plate of a sundial which permit us to tell the time from the
shadow cast by the style. Hour lines are drawn for hours and sometimes for
half-hours and quarter-hours but much more rarely for 5 minute intervals.
Declination Lines: lines drawn on
the dial plate of a sundial which permit us to determine the date from the
shadow cast by the style. It is conventional to show the dates on which the Sun
enters certain signs of the Zodiac, for example, for the Sun declination 0°
(Aries and Libra), +/- 11° 29' (Pices and Virgo), +/- 20° 20' (Gemini and
Sagittarius). These lines are also called diurnal
arcs.
Longitude
Longitude of a place: the angle formed by the meridian of a place with the Prime
Meridian in Greenwich.
Longitude is positive for locations to the west of Greenwich and negative for those to the east.
Longitude correction
The time difference between the location's meridian and the
time zone’s meridian (Greenwich or local time zone). There is a difference of 4
minutes for each degree of longitude.
For example, if you buy a sundial made for Roswell,
New Mexico, at longitude 105° W. and place it
in Tucson, Arizona at 111° W., it can be off by about
24 minutes.
Mass Dials
Also known as ‘scratch dials’; these were inscribed on a
buttress or wall close to the porch of a parish church in the Middle Ages used
to indicate the time for religious service or gathering.
Mars Sundial (MarsDial)
The sundial on board NASA’s Mars Exploration Rover Spirit,
which landed on Mars in January 2004.
Mean Solar Time
See: Equation of time.
Meridian:
Off a place: the geographical meridian which passes through
a place.geographic: the great circle passing though the poles and the zenith of
a place.
Meridian Dials
Also known as ‘Noonmark
Dials’.
Nodus
Nodus: An indicator or marker on the gnomon that helps to define an exact point on the shadow.
Noonmark Dials
Also known as ‘Meridian
Dials’
The simplest sundials do not give the hours but note the exact
moment of 12:00 noon used historically to correct mechanical clocks sometimes
so inaccurate as to lose or gain significant time daily.
In U.S. colonial-era houses a noon-mark can often be found
carved into a floor or windowsill indicating local noon providing a simple, accurate
time reference for households that do not possess accurate clocks.
Even today in some Asian countries post offices have set
their clocks from a precision noon-mark.
The typical noon-mark sundial was a lens set above an
analemmatic plate, an engraved figure-eight corresponding to plotting the
equation of time versus the solar declination.
When the edge of the sun's image touches the part of the
shape for the current month, it indicates noon.
Pillar Dials
Also known as the Pyrenean
Shepherd’s Dial or Cylinder Dial (see under Cylinder Dials).
Polar Dials
A type of sundial in which the plane of the shadow-receiving
surface is parallel to the polar axis.
Polestyle
See: Gnomon.
Polyhedral Dials
Combining various orientations on multiple faces showing,
for example, faces oriented to tell time in various world cities.
Pyrenean Shepherd’s Dials
Also known as ‘Pillar
Dial’ or ‘Cylinder Dial’ (see under Cylinder Dials)
Reclining Dials
See under Vertical
Dials.
Renaissance Focusing Sundial
See under: Renaissance Sundial.
Renaissance
Sundial
A patented sundial which illuminates the time with a crisply
focused beam of light, rather than casting a fuzzy shadow.
Cylindrical focusing mirrors on the triangular support
project a sharply focused beam on the inside of the helix. A timescale on the
inside of the helix directly reads watch time generally to within 30 seconds of
the atomic standard, when properly set up.
Ring Dial
A ring dial is for use in a fixed latitude and is a small
portable dial in the shape of a cylindrical ring for determining time. See also Universal
Ring Dial.
Sawyer Equant Sundial
This dial reads solar time on its bronze plate, and civil
time on its granite plate. Both sundials adjust for latitude using a precise
patented wedge mechanism.
Scaphe Dial
The scaphe (or
skaphe, also scaphium or scaphion) from the 3rd century BC and was a
sundial consisting of a hemispherical bowl with a vertical gnomon inside it,
with the top of the gnomon level with the edge of the bowl. Twelve gradations
inscribed perpendicular to the hemisphere indicated the hour of the day.
Scaphium Sundial
See under: Scaphe Sundial.
Scaphion Sundial
See under: Scaphe Sundial.
Skaphe Sundial
See under: Scaphe Sundial.
Scratch Sundial
See under Mass Dials.
Solstice
The moment in the year when the Sun reaches in maximum declination in the north or south of the
celestial equator. The Summer Solstice (21 June) in Europe
is the longest day of the year and the Sun is in its highest position in the
sky. The Winter Solstice (21 December) is the opposite — the shortest day and
the lowest point the Sun reaches in the sky.
Spot-On Sundial
Its unique feature is the split gnomon, which casts the
shadow and every day at noon a line of light shines between the 2 plates for
around 5 minute’s; this feature allows them to be set up precisely, so that it
will tell the right "time by the sun" for years to come.
Style
The name given to the shaft or triangle which casts its
shadow on a dial. A polar style is oriented parallel to the Earth's axis. A vertical
style or gnomon is placed vertical to the dial plate.
Sub-style
The line corresponding to the projection of the style on the dial plate of a sundial.
The angle which the sub-style makes with the noon hour line indicates the declination of the dial.
Suncatcher
A
suncatcher
or light catcher is a small, reflective glass or for example mother of pearl
piece that is hung indoors, so that it "catches the light" from a
nearby source, usually hung at windows.
The South-western American Indians first began making them
and they are now still popular in that region
Suncatchers
may be mass-manufactured, or they may be created by hand, and can be of varying
simplicity of design from an arts and crafts project to a professionally
handmade glass sculpture.
Some designs are simple and abstract with perhaps some
mobile-like chained elements, while more
complex designs often evoke plants or animals.
A
suncatcher
is something like the optical equivalent of a
wind chime,
and indeed many designs combine the two.
Sundial
A device for telling solar time from the position of the
Sun's shadow thrown by a gnomon. If the
dial is a horizontal or vertical plate, the hour lines are at unequal angles to
each other. A vertical dial, which faces
one of the cardinal points of the compass, is called a direct dial; one which does not is a declining dial.
The Concise Oxford dictionary defines it as an instrument
showing the time by the shadow of a pointer cast by the sun on to a plate
marked in hours.
Thew Patent Dial
A sundial which uses numbers (for example ) cut-out of a
strip or band to let light in the shape of that number aligned with a fixed
marker on a surface below it to indicate the time.
Time-Mark Sundial
Sundials with an engraved message on the side of the gnomon
to give a unique gift for an anniversary, birthday, wedding, or special event
and the simple variant of the Time-Mark sundial idea in which the gnomon is actually
set to indicate the specific time/date for the occasion concerned rather than
the solar time.
Time Differentials and the need for (some)
Adjustable Sundials
There is a major difficulty
for sundials in some countries.
Spain for example keeps
Central European Time, even though most of Spain is west of the Greenwich
meridian. This means that there is always a difference of at least one-hour
between sundials and clocks in Spain, and in summer time, a difference of more
than 2 hours. A sundial in Pamplona should have a difference of around 2 hours
and 15 minutes, since Pamplona is nearly 4 degrees West of Greenwich.
Universal Equinoctial Ring Sundial
See: Equinoctial Sundial.
Universal Ring Dial
A Ring Dial is
for use in fixed latitude, but the universal ring dial can be used over a wide
range of latitudes. It consists of three rings and a strip with slider. A flat
vertical brass ring, with grooved outer edge, fits within a ring of circular
cross-section, and slides within it. The outer ring is suspended from a shackle
or mounted on a foot. One side of the inner ring carries a scale of degrees,
0-90, for adjustment to latitude using an index on the outer ring. Pivoted
within the inner ring is a further ring which can be swung out at right angles,
carrying the hour scale.
University of Hawaii Sundial
This sundial is one of many sundials that are more
accurate--to within four seconds--than the famous Egyptian prototypes.
Vertical Dials
Vertical Dials and Reclining
Dials are basic types of sundial.
With a vertical dial the plane of the shadow receiving
surface is vertical and for a reclining dial it is horizontal.
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