Sundial Plaques

The longitude of the Caroline Bay, N.Z. sundial is 171.25 degrees
and the longitude correction is 35 minutes. Read the instructions on the plaque.
Here is the calculation for the longitude correction: 60*(180-171.25)/15)

Note the counter-clockwise arrangement of the Roman numerals in New Zealand.
The small sundial in front of (south of) the large sundial shows how the time correction is arranged. Right click for a larger image. The gnomon points to geographic north, which in this case is at 12:30, not 12:00. The photo was taken on 9/1/13, 11:30 MDT. The time correction in the chart for September 1st is (-)2 minutes, and the small sundial is accurate to within a minute in this photo.
The longitude of the Carefree, AZ sundial is -111.92 degrees and the longitude correction is 27.7 minutes. Latitude 33.82 degrees.
Local solar time (sundial time), plus the longitude correction (27.7 minutes), plus the equation of time correction, which varies throughout the year,
equals mountain standard (clock) time.   See the photo on the right, of the small sundial in front of the large sundial  >>>>>>

Zaragoza sundial, Spain. Gnomon 46 meters long, height 30.34 meters, said to be the largest horizontal sundial in the world. Right click on these images to enlarge.

Beautiful, unique plaque, in front of the sundial.

Closeup of the plaque showing the equation of time.
The graph states that in mid-January and March "DIAL IS 10 MINUTES FAST".
However, Sundial time is slower than watch time at the beginning of the year.

Ingleside Terraces Sundial. Temporary plaque to the left of the stairs.
See also Sundial slides and Fax Art

Times are listed in two minute intervals and the time adjustment can always be read
to the nearest minute, which is the limit of accuracy for a sundial.
Copyright 2021. Numerical data is from NOAA.

Replacement plaque installed November, 2022. Right click or press and hold to enlarge. There are disadvantages to this location on the north side of the gnomon.

UC Berkeley sundial
The UC Berkeley Class of 1877 Sundial, installed in 1915, is located just south of the Campanile. It includes a chart showing how many minutes need to be added to sundial time to obtain local time. An additional minute must be added to Berkeley sundial time to obtain Ingleside Terraces local time. Right click these photos for a large image.
Sundial Bridge plaque
The Sundial Bridge in Redding uses small plaques as markers which give PDT clock time. This obviates the need for an equation of time plaque, and is fairly accurate in the middle of the day Sundial Bridge accuracy.

Stonehenge heelstone
The Stonehenge heelstone can be considered to be a plaque that shows where to stand to see the sunset on the winter solstice, marking the return of the sun and the beginning of a new year. Right click for a larger image.
Stonehenge winter solstice sunset
The NOAA solar calculator shows that a line for sunset on December 21, 1000 (as far back as that calculator goes), starting at the heelstone, goes through the center of the Stonehenge sarsen stone circle, showing remarkable accuracy for a structure built 4500 years ago.

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Robert Karis

Alphabetical index
Extreme sundials
Geographic north
Ingleside Terraces Sundial
Sundial accuracy
Sundial Bridge accuracy
Sundial factoids
Sundials EOT tables