Sundial Facts and Factoids

factoidAn assumption or speculation that is reported and repeated so often that it becomes accepted as fact.

IT Sundial gnomon height
  • The 1914 Sundial booklet states that the gnomon of the Ingleside Terraces Sundial "rises to a height of twenty-six feet". However, as the above photo shows, with a 5'2" person standing to the next to the gnomon, the height of the gnomon is closer to three times the height of the person than to five times the height. There are webpages which also confuse the height and length of the gnomon.
    Measurements were performed many years ago with someone dropping a rope from the top of the gnomon, and the results were length of gnomon 28 feet, height of gnomon 17 feet, consistent with a latitude of 37 degrees.
  • There are several articles and webpages which state that the Ingleside Terraces sundial is synchronized with or calibrated to the summer solstice. For example, sfgate 4/14/2002, updated 1/30/2012, "Ingleside Terrace Giant Sundial": "synchronized to the summer solstice in June."  AtlasObscura.com "Urbano Sundial": "Synchronized to the summer solstice..." San Jose Mercury News 2/18/2020: "If you visit on the summer solstice in June, the time will be exact."
    The above statements are not correct. As demonstrated on other pages on this website, the gnomon points to geographic north which is at 12:00 sun time.  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
  • When the Ingleside Terraces sundial was built in 1913, there were many newspaper articles and ads stating that it was the largest sundial in the world. It was not; there was and is a larger sundial in Jaipur, India. As the Jaipur sundial is not mentioned in the 1911 Encyclopedia Britannica, it would have been difficult for San Franciscans at that time to know about it. The Ingleside Terraces sundial was most likely the largest sundial in the United States when it was built.
  • The Vrihat Samrat Yantra sundial in the Jantar Mantar observatory in Jaipur, India is the largest sundial in the world. There are claims on the web that it can be read with two second accuracy, which has not been documented.
  • IT Sundial ad
    Ad for Ingleside Terraces and "The Largest Sun Dial in the World", San Francisco Chronicle, October 4, 1913.

    Ingleside Terraces Sundial links:
    Google map, directions to the Sundial
    Ingleside Terraces Sundial, Then and Now Photos
    Ingleside Terraces Giant Sundial
    Kite Aerial Photographs
    Sundial History
    Creative Commons License
    Robert Karis
    www.sfog.us
    Alphabetical index
    Geographic north
    Ingleside Terraces sundial
    Sundial accuracy
    Sundial plaques
    Sundials EOT tables
    The North American Sundial Association has a registry of over one thousand sundials in North America, including the Ingleside Terraces Sundial, which is number 82.
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