Sundials - World's Oldest Clocks

North American Sundial Society

Transits Time and Longitude

Here we showcase various natural and scientific phenomena related to the sun and solar alignments, and the quest for measuring time and longitude.

NASA has taken outstanding video of the June 6th 2012 transit of Venus.  Images were recorded by the NASA Solar Dynamics Observatory Satellite that records the sun's surface and corona at a number of visible light and ultraviolet wavelengths. [See]   These images showing the 2012 transit of Venus were recorded at a wavelength of 171 Angstroms (AIA 171) (Extreme Ultraviolet).  This channel is especially good at showing coronal loops - the arcs extending off of the Sun where plasma moves along magnetic field lines. The brightest spots seen here are locations where the magnetic field near the surface is exceptionally strong.  

NASA video source and images may be found at

Don’t miss the Solar Eclipse this Sunday, May 20th.  Times of the eclipse can be found at

For those of you in the San Francisco – San Mateo California area, Bill Gottesman, NASS dialist, has created an “eclipse clock”, a new type of paper sundial made specifically for the partial solar. You need a simple pin-hole projector (a card with a small hole in it) to cast a shadow of the eclipsed sun.  The angle of the moon’s shadow tells accurate time (at least for San Mateo California). Bill will discuss how he made this dial at the NASS Sundial Conference in Asheville this August.  Come find out how he did it.

Download this file (eclipsedial.pdf)Eclipse Sundial - May 20, 2012[Gottesman Eclipse Sundial for San Mateo CA]714 kB


Want to watch a sundial in action?  Professor Woodruff Sullivan and Ian Smith at the University of Washington in Seattle have just launched an active webcam of the University’s large vertical declining sundial on the side of the Physics and Astronomy building.   The webcam image is updated once per minute day and night. “we know that some of you will want to stare at it for hours on end (or at least bookmark it….”

Their website has many features including the first two time-lapse movies of the giant sundial showing the all-day shadow on the summer solstice and on the autumn equinox. More time lapse videos will be presented during the months that come.  In the near future they will improve the present camera with higher-resolution and greater reliability.

A flurry of sundial webcams existed in 2004-05 when the EarthDial Project, the invention of Bill Nye and Woody Sullivan, was run under the auspices of The Planetary Society. The Project, with a motto Two Worlds, One Sun was run in conjunction with the MarsDial Project, which involved the Mars Exploration Rovers Spirit and Opportunity, each of which landed on Mars in 2004 with a small calibration target turned into a Mars sundial on its deck. People around the world were urged to build sundials of a standard design and display them to the world using a webcam. Click Here to See Time Lapse Movies of Some of These Dials.  A new Mars sundial will arrive red at the red planet next August onboard Curiosity.

Take a look at the new webcam at