This is a web page about the vertical sundial on the south facing wall of our home at 2 Forest Lane, San Carlos, California. For those not familiar with this region, San Carlos is approximately 25 miles south of San Francisco.  It was installed Easter Sunday, April 4, 1999. I've been interested in sundials for a long time, but I've never undertaken a project this large before. This sundial has been a labor of love for approximately 1 1/2 years. Some of the time was spent developing the equations to create the sundial. Some of the effort involved determining the precise angle of the wall off of south. This actually required taking some noon observations and using trig to determine the precise angle of a shadow relative to the perpendicular of the wall. Creation of a foam core model to check the accuracy and appearance also took a great deal of time. The majority of the time though was spent building the sundial. The TWO FOREST LANE SUNDIAL is a large vertical dial that is mounted near the peak of the roof on the south-east facing wall of our home. This position allows the dial to be visible from Graceland Ave. When viewed from this street, the closest viewing distance is approximately 30 feet and the opposite side of the street makes for a viewing distance of approximately 55 feet. This location is very special because Graceland is a particularly pretty street. We have many people walking by even though there are no sidewalks on this street. I hope many of the passerbys find my sundial interesting. As I state below, I believe this sort of vertical sundial to be extremely rare in this area. I've placed a wood and Lexan literature box in the garden area outside the fence next to the sundial. I want to make sure that those who are interested can take a brochure and fully understand how to read the dial. The last thing I want is for people to believe the dial is inaccurate. This sundial is able to be read to approximately two minutes of "clock time" anytime during the year. back to top

VERTICAL-DECLINING SUNDIAL

LATITUDE- 37° 29' 21.4"

LONGITUDE- 122° 15' 57.3"

Pacific Standard Time (our local clock time) may be read from this sundial to an accuracy of approximately 2 minutes. Find the current or closest date below and either add or subtract the number of minutes shown to find the time. If we are currently observing Daylight Saving time, be sure to also add 1 hour.

THE EQUATION OF TIME BELOW HAS BEEN ADJUSTED FOR THE LONGITUDE IN SAN CARLOS, CA AND CORRECTED (-2 MIN.) FOR MOUNTING ERROR. DO NOT USE FOR OTHER LOCATIONS OF A DIFFERENT LONGITUDE!

All sundials have a gnomon, this one having it done in stainless steel. The gnomon is the triangular metal piece mounted perpendicular to the face of the dial. The height and angle of the gnomon to the dial face and the angle away from the vertical 12 o'clock line are all specifically calculated. In fact, the calculations for this dial were performed by a personal computer processing complex hyperbolic trig equations in Excel. The resulting output required to make this dial amounted to a dozen pages.

The hour lines range from 5 A.M. to 1P.M., with five 10 minute marks in between adjacent hour lines. The upper curved line is called the Tropic of Capricorn. This arc depicts the path of the sun's shadow on Dec. 22 when the relative height of the sun above the horizon is at the lowest . The lower curved line is called the Tropic of Cancer. This curve shows the path of the shadow at the sun's highest arc which occurs on June 21. The straight line angled downwards through the middle of the dial is the equator line. The sun's shadow will trace this straight path two times a year- once on March 21 as we're moving towards summer and again on September 23 as we head into winter.

The Equation of Time provided above in chart form has been altered for this specific location. Nine minutes has been added to the standard numbers because San Carlos is nine minutes "later" than the Pacific Standard time meridian, which is located at 120 degrees West. In other words, a sundial located at the east side of Stateline Point at North Lake Tahoe, just barely into Nevada, would report the accurate clock time after being adjusted by only the equation of time. The Equation of Time is required partly because the earth moves more quickly in its orbit when closer to the sun than when farther away, and in part because the sun's apparent path is more of an elliptic, than on the Earth's equator.

Sundials of this type are more common in Europe than America. I know of no other sundial of this design in the immediate region. In this age of digital clocks, it's reassuring to see the relationship between the sun and earth shown as time, interpreted by a sundial of ancient design. Most people find it amazing that a well designed sundial allows a person to set a clock or watch to within a couple of minutes of the actual time. I hope this brief explanation of my Vertical Declining sundial has been informative. For individuals interested in more information on sundials, the following books are highly recommended:

SUNDIALS THEIR THEORY AND CONSTRUCTION , Albert E. Waugh 1973

SUNDIALS, R. Newton. Mayall and Margaret W. Mayall 1973

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Thanks for visiting the

Two Forest Lane Sundial website!

*Ken S.*