Ingleside Terraces Sundial
San Francisco
Ingleside Terraces sundial, aerial view San Francisco sundial, aerial view
The Ingleside Terraces Sundial on Entrada Court was built at the at the time of the original development of Ingleside Terraces. As evidenced by the plaque at its base, it was dedicated on October 10, 1913, the same day as the "meeting of the waters" in the Panama Canal.  The gnomon is 28 feet long. The diameter of the dial with Roman numerals is 34 feet. The shadow of the gnomon moves one inch per minute on average, but only 1/2 inch per minute from 11 A.M. to 1 P.M. The Hilltop Park sundial in the Bayview District of San Francisco was built by the San Francisco Redevelopment Agency in 1978.
SF Chronicle article 10/2/1978

How to tell time with the Ingleside Terraces sundial:
Ingleside Terraces sundial sun time
10:00 sun time, 10:00 PST Dec 2
From December 2-5, sun time and clock time are the same (within a minute) in Ingleside Terraces.
Ingleside Terraces sundial sun time
11:36 sun time, 12:00 PST Feb 11
In February, sun time is up to 24 minutes behind Pacific Standard Time in Ingleside Terraces.

12:00 sun time, 13:11 PDT Jun 20
Summer solstice, shortest shadow of the year.

Doesn't work if it's foggy.

15:45 sun time, 16:37 PDT Nov 1.
Note the use of the Roman Numeral IIII instead of IV.
Use the left edge of the shadow in the morning and the right edge in the afternoon. At solar noon the shadow of the gnomon lies between the two metal rods at XII.
Right click the images to view larger images and the 15', 30', 45', and 1 hour time markings in the concrete.
cf.Ingleside Terraces Sundial accuracy

Solar Noon, 12:00 on a sundial, occurs in San Francisco at the following local times (for the 21st of each month, 2015):
January 12:22 PSTApril 13:09 PDTJuly 13:16 PDTOctober 12:54 PDT
February 12:24 PSTMay 13:07 PDTAugust 13:13 PDTNovember 11:56 PST
March 13:18 PDTJune 13:12 PDTSeptember 13:03 PDTDecember 12:08 PST

Each hour from noon to 6 is placed farther apart, measuring from the base of the gnomon: noon 0°, 1 P.M. 9°, 2 P.M. 19°, 3 P.M. 31°, 4 P.M. 46°, 5 P.M. 66°, 6 P.M. 90°.
Ingleside Terraces sundial 10/18
Photo October, 2018.  The diameter of Sundial Park is more than 150 feet which gives it an area of about 18,000 square feet,
which is the largest single parcel of land in Ingleside Terraces.
  • Sundial accuracy requires precision in all three axes: x) the gnomon must point to geographic north;
    y) the gnomon cannot tilt to the left or right; and z) the angle of the gnomon must equal the latitude in degrees.
    The 1913 Ingleside Terraces sundial is doing very well in all of these measures:
    Geographic north   Ingleside Terraces Sundial accuracy
  Sundials in the northern hemisphere point to geographic north and the angle of the gnomon is equal to the latitude so that the gnomon is parallel to the earth's axis. The gnomon always points to Polaris, the North Star. If you stand next to the Ingleside Terraces Sundial at night and look up the gnomon, you will see Polaris.
  A sundial at the north pole could be a vertical pole with 24 hour markers placed at 15° intervals around it, so that it could be used to tell time 24 hours a day in spring and summer, if its position didn't change and if it were sunny.
  Sundials in the southern hemisphere point south and the shadow of the gnomon rotates counterclockwise.

[+] How to convert from sundial time to clock time
[+] Sundial Bridge, Redding
Ingleside Terraces sundial, enhanced aerial view
Ingleside Terraces Sundial Centennial 2013.
This photo is an enhanced 2013 Bing maps aerial view.
Ingleside Terraces sundial, winter solstice
Ingleside Terraces Sundial winter solstice 2013
Longest shadow of the year at noon.

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
Alphabetical index
Extreme sundials
Geographic north
Point of Infinity
Sundial accuracy
Sundial Bridge accuracy
Sundial factoids
Sundial plaques
Winter solstice