Sundials

A sundial is an instrument which determines the time from the sun by using an indicator called a style (part of its gnomon) to cast a shadow or to project a spot of light onto a graduated surface.  The time obtained (sundial time) is termed apparent solar time.  It differs from clock time by an amount known as the equation of time (EOT).

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ACLE  –  ST EDMUND

 

CDCADB43-462E-4BE9-A795-BD92EA918374Located at left hand side of porch entrance

 

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SOUTH WALSHAM – ST MARY

 

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 Classification and description

Medieval Scratch Dials (Mass Dials)   –  12th – 14th Century

Scratch dials can be found on the six surrounding churches, examples of which can be seen above.  The gnomon was a straight stick wedged into a central hole, unlike the vertical sundial we know today.

The shadow casts a non-linear time moving shadow creating a time system based around the church services throughout the day.  It also ties in with the farming community’s working day.

Medieval time system (canonical hours)

  1. The day (sunrise to sunset) was divided into 12 hours.
  2. The 1st hour of the day starts at sunrise.
  3. The 12th hour of the day ends at sunset.
  4. As the year progressed from summer to winter, each hour in the morning grew a little bit later and each hour in the afternoon grew a little bit earlier as shown in the table below.

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The medieval system was more a day planner than a true time measuring system.

The sundials we know today developed from these primitive sundials.  The latter scratch dials have marking spacing similar to a south-facing vertical sundial.

 

 

 

Peters Wood Sundial, built 2017

 

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Classification and description:

The three declining sundials are set on S-E, S-W and N-W planes.  They are all secondary dials.  The S-E dial is known as a great declining dial because it nearly faces due East.  Other examples of declining sundials can be seen at Peterborough Cathedral (great decliner) and Howard House, King Street, Norwich (S-E decliner).

 

Lingwood Millennium Green Sundial, built 2016

C03F0869-2285-424F-9D3A-365C79B19C1FSundial noon (11th April)

 

7735717F-99EA-46C6-9468-45EA23EC63A7.jpegBST 13:00 23rd September

 

Classification and description:

The noon mark sundial gives the precise time when the sun is due south, i.e. sundial noon.  The smaller, circular markers relate to GMT as shown in the diagram below.

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Farrow’s Wood Sundial, built 2014

 

 

Classification and description:

A polar sundial without range extension lugs.

The dial face is drawn on the polar plane (parallel to the earth’s polar axis at the given latitude of the sundial location).

  1. The dial face relates to the trignometrical tangent ratio.
  2. Time indicated is the azimuth of the sun’s position in the sky.
  3. It is a primary reclining sundial.
  4. Together with the equatorial sundial, it has universal dial face divisions regardless of its location.

Other examples of the polar sundial can be seen at:

  1. The Millennium Footbridge beside the City of London School for Boys
  2. Midway between the Thames Barrier and the east side of the Greenwich peninsula.

 

Austin’s Wood Sundial, built 2013

 

Classification and description:

A cube sundial with 5 of the 7 primary sundial planes.

Built from black granite which came from Tamil Nadu, Southern India and built by Abbey Memorials.

The construction and installation of the cube sundial took place over a two-year period (2012/2013).

The slideshow below highlights the technologies used in the making of the sundial. From computers and laser cutting equipment to satellite navigation equipment, a large selection of mechanical aids were also used in the transportation and installation of the sundial.

 

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Jubilee Wood Sundial, built 2007

 

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Classification and description:

Human analemmatic horizontal sundial

The gnomon is a vertical post (human) moved about from place to place according to the sun’s altitude.  The dial does not have hour lines in the usual sense but hour points which fall along the circumference of an ellipse.

The time indicated on the dial is known as local apparent time (solar time).  The two scales relate to GMT and BST; however to convert to watch time, both the equation of time and longitude correction need to be applied.

Other examples of the human analemmatic horizontal sundial can be found at:

a) The Old Palace Yard, Houses of Parliament, London
b) Blickling Hall Gardens, Norfolk.

 

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