Sundial, Huang Engineering Center - Stanford, CA
Posted by: 
DougK
N 37° 25.669 W 122° 10.429
10S E 573097 N 4142653
This sundial was relocated to the Huang Engineering Center after the Terman Engineering Building was demolished. It was design in 1997 by Professor Ronald Bracewell.
Waymark Code: WMH5D4
Location: California, United States
Date Posted: 05/25/2013
Views: 6
This sundial used to hang from the
Terman Engineering Building at Stanford University. The sundial was designed by Prof. Ronald N. Bracewell and built by his son Mark C. Bracewell in 1997. Professor Bracewell wrote the an article for the
Civil Engineering newsletter (p.17), that year:
Sundials of various kinds have been known since antiquity when they served as public indicators of civil time. The sundial, depending as it does on the rotation of the Earth, offers fundamental accuracy.
On looking at the new sundial on the wall of the Terman Building one is struck by the elongated figure-eight curves, one for each hour. What are these curves? If you had a south-facing office in the building you could place a camera on the window sill and take a photograph of the sun at twelve noon by your watch. If you did this once a week for a year, making all the exposures on the same frame of film, your final print would be a figure-eight curve, pricked out by 52 dots. This curve is called the analemma.
The central hole in the disc that stands 3.16 inches out from the?new sundial corresponds to the camera lens while the substrate that receives the spot of light through the hole, or oculus, corresponds to the film plane. Therefore, each day when it is noon the spot of sunlight on the sundial will be on the analemma, and similarly for other hours.
There are two moments each day when the light spot crosses the analemma. Which gives the right time? That depends on the season. Green indicates Spring (starting from the vernal equinox on March 20/21 and ending at the Summer solstice on June 21/22), red is for Summer, orange for Autumn, and blue for Winter. On March 20 or September 22 you would notice that the spot of light moves upward along the straight line labeled AEQUINOX, while at the Summer solstice (June 21/ 23) the spot would move along the lower hyperbola labeled SOLSTICE. At the Winter solstice (December 21/23) the spot would advance up the top hyperbola.
When the Terman Building was demolished, the sundial was remounted at it's current location on the Huang Engineering Center. A plaque on the wall beneath the sundial mounting reads:
CÆLUM SCRUTANDO LEGES MOTUS DIDICIMUS
We learnt the laws of motion by studying the heavens
The mural sundial at Stanford is descended from a solar clock that once graced the Tower
of the Winds in the Agora in Athens. This one has an analemma for each hour, color coded
for season, showing time that is accurate to the minute without correction for date. You can
set your watch by it.
Each day on the hour the circular spot of sunlight thrown by the oculus will fall on the
analemma for that hour and will tell the season, sap green for Spring, cherry red for Summer,
autumn gold for Fall, and ice blue for Winter. At the equinox the spot of light moves up the
straight line marked ÆQUINOX. At the Summer solstice the spot moves up the hyperbola
labeled SOLSTICE; at the Winter solstice the spot traces out the upper hyperbola.
[Etching of the sundial face]
The Latin motto reminds us that Newton's three laws that govern everything that moves
originated in astronomy. A second motto, d/dt ? 0 signifies, in the notation of the philosopher
Leibnitz, that time does not stand still - an admonition to us all that time is precious.
The sundial project was initiated by Professor Robert H. Bracewell and supported by
Dean James F. Gibbons. The sundial plate was hand carved by Mark Bracewell and hung
under the auspices of Dean John L. Hennessy.