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Sundial Factoids | ![]() |
factoid: An assumption or speculation that is reported and repeated so often that it becomes accepted as fact.
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The above statements are not correct. As demonstrated on other pages on this website, the gnomon points to geographic north which is 12:00 sun time, solar noon. This is true every day of the year. At the summer solstice, 12:00 sun time occurs at 1:11 P.M. Pacific Daylight Time. On December 2-5, sun time and clock time are the same (within a minute) at the Ingleside Terraces sundial. Clock time can be determined from sun time by using the equation of time and the longitude correction as shown in the charts on this page: Sundials EOT tables. The excellent accuracy of the Ingleside Terraces, within a minute on multiple dates throughout the year, is demonstrated in this page: Ingleside Terraces Sundial accuracy |
![]() Ad for Ingleside Terraces and "The Largest Sun Dial in the World", San Francisco Chronicle, October 4, 1913. The Ingleside Terraces sundial was most likely the largest sundial in the United States when it was built. However, there are larger sundials in India, built in the 1720's. |
The gnomon (hypotenuse) length of the Delhi sundial is 128 feet, and this sundial, with its approximately 100 stairs, is obviously much larger than the IT sundial. |
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Point of Infinity Sculpture, 69 feet tall, on Yerba Buena Island, San Francisco.
The San Francisco Arts Commission says that "The sculpture acts as a monumental sundial...A stone marker will be placed in the plaza to mark the precise location of the noon shadow on the spring and autumnal equinoxes."
An article in the New York Times states that it is a sundial with "a granite marker on the ground to align with the shadow cast by the artwork at solar noon on days of the spring and fall equinox". These articles overlook the fact that every vertical structure in the northern hemisphere (above the Tropic of Cancer) casts a shadow that points due north (360 degrees, geographic north) at solar noon every day of the year, not just at the equinoxes or the solstices.
Despite the articles referenced on the left, the marker was not placed at 360 degrees, geographic north, as can be seen in the above photo.
3/20/25 12:19:10 PDT (58 minutes before solar noon on the spring equinox) the shadow of the Point of Infinity sculpture points to the granite marker. Latitude of Point of Infinity Sculpture 37.81047, longitude -122.36886. The azimuth of the sun is 157.2 degrees, and the shadow points towards the marker at 337.2 degrees NOAA.
On the autumnal equinox, 9/22/25, the azimuth will be at 157.2 degrees and hit the granite marker 15 minutes earlier, at 12:04:12 P.M. PDT.