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.

At the Grolier Club on the Upper East Side of Manhattan is a massive exhibit  On Time: The Quest for Precision curated by Bruce Bradley.  The exhibit presents the progress of timekeeping over six centuries through 86 rare books from the Linda Hall Library of Science, Engineering & Technology.

La pratique et demonstration des horloges solaires
1624 La pratique et demonstration des horloges solaires

Journalist Allison Meier of describes a number of books on display such as "German cartographer Sebastian Münster’s 1533 Horologiographia, the first book devoted to sundials, with woodcuts attributed to Hans Holbein the Younger."  As shown in her photo, "French engineer Salomon de Caus’s 1624  La pratique et demonstration des horloges solaires has embedded pop-ups to make the workings of its sundials easier to replicate."

The scope of "On Time" stretches from sundials, to water clocks, mechanical clocks and even a Pilkington & Gibbs Heliochronometer, ending with our latest atomic clocks.  The display flirts with the possible.  While Benjamin Franklin may have suggested using hourly time-telling canon in the 18th century, Athanasius Kircher proposed a fanciful firing sundial a century earlier in his 1646 Ars magna lucis et umbrae in decem libros digesta. His bowl-shaped sundial holds gunpowder at the hours that is ignited by the rays of the sun from a lens.  In turn the firing gunpowder triggers hammers to toll hourly bells. If one thinks about this for a moment, Kircher's proposal is as unrealistic as Franklin's.  The change in solar declination creates problems for proper placement of the gunpowder, let alone directing the ignition to trigger hammers.

Allison observes that "These manuscripts affirm the centuries of shared ideas that give our modern timekeeping devices their precision."  On Time: The Quest for Precision" continues through November 19, 2016.

Read more at:

What do Omega Psi Phi fraternity of Howard University Washington DC, Merton College in Oxford, Nashotah House Theological Seminary in Wisconsin, and Lewis Carroll's poem Jabberwocky all have in common?  Dancing and ceremonies around a sundial!  In Carroll's poem of 1885 "the slithy toves did gyre and gimble in the wabe" and as Alice explains to Humpty Dumpty, “Toves are curious creatures that are something like badgers, something like lizards, and something like corkscrews. They make their nests under sun-dials and live on cheese." and “Wabe is the grass-plot round a sun-dial. It is called like that because it goes a long way before it, and a long way behind it. And a long way beyond it on each side."

At Howard University in the center of the main campus quadrangle is a bronze sundial on a 3-foot fluted limestone pedestal, gifted in 1929 to the university in honor of Benjamin Banneker, surveyor of the city of Washington DC, clockmaker, and sundialist. 

Read more: Sundials and Timely Ceremonies

With all due respects to Shakespeare, time will always be with us, and signifies quite a lot. The Harvard-Smithsonian Center for Astrophysics is organizing a symposium dedicated to Time and Culture to be held 5-9 June 2016 at Harvard's Northwest Lab.  According to the symposium organizers:

"The symposium aims to set the stage for future timekeeping standards, infrastructure, and engineering best practices for astronomers and the broader society. At the same time the program will be cognizant of the rich history from Harrison's chronometer to today's atomic clocks and pulsar observations. The theoreticians and engineers of time will be brought together with the educators and historians of science, enriching the understanding of time among both experts and the public."

The definition of the second has changed several times over the last 40 years and likely will change again before the end of this decade. Should timekeeping be decoupled from the rotation of the earth?  We already abstract time with zone time (such as Eastern Standard Time) and minipulate it to fit our activities (using Eastern Daylight Saving Time).  We no longer worry about the moment of sunrise or sunset, rather that we go to work at 9:00AM or have a class that lasts from 10:00-10:50AM.  Indeed, "ante and post meridian" may be obsolete.  

"The future of timekeeping is evolving with the development of optical frequency standars, the consideration of high-order relativistic effects, and the challenges of distributing trusted timescales at even higher preicision....A closer look at time in astronomy and other sciences, as a defining element of modern civilization, is needed."  Read more and register for the symposium at:

Greenwich Globe - Alisa Goikhman

Alisa Goikhman has put into art  a sculpture called the Greenwich Globe.  What started as a simple idea of dividing Canada and the US into time into time zones 15o wide (one hour steps), today's meridian boundaries create a complicated map.  Goikhman projects this map onto a globe with the ragged ridges of each time zone, sequentially enlarging the meridians using the proportions of an Archimedes spiral.

Goikhman explains: " The Greenwich Globe's shape was generated by an algorithm that treated time as physical matter.  Each additional hour is represented through a constant degree of elevation and a 15o angle bend.  The elevation based map projections gives easy-to-read shape to the complex man-made system of time-zones.  It also operates as a sundial, a play on the now familiar row of world time clocks.  The shadow it casts on a wall is meant to be read as a world watch.  Each spike in the shadow shows the local time at a corresponding geographical region."

Read more: Greenwich Globe

Kevin Murphy, artist and photographer, set up a time-lapse camera on the roof of the San Francisco Exploratorium to record the sky every 10 seconds, 24 hours per day for an entire year. The camera points due north at and elevation of 45 degrees, which means that you won’t see any dramatic sunrise or sunset, nor will you see a burning image of the sun. Even with the wide-angle lens, the sun is always kept just out of view. But what a wonderful view of the sky: Look closely at the video and you’ll see moving clouds, fog, rain, and differing colors of the sky.

Most stunning is the changing length of the day. Summer morning twilight begins about 4:10am (Pacific Standard Time) and evening twilight ends about 8:10pm, but you must be patient for the winter sky to appear. Winter morning twilight begins about 6:50am (PST) and evening twilight ends about 5:30pm. (There’s a small running clock in the bottom right corner to chart your progress). You’ll see the dramatic difference between summer and winter with days in darkness patiently waiting their turn at sunrise and conversely, the fast quenching of the blue sky into darkness well before the summer frames show any sign of paling.

Each frame is digitally photographed at 1024x768 pixels, that with compression, requires about half a terabyte storage per year. Kevin Murphy has been creative with the sky display: Thumbnail videos of each day of the year are collectively represented in a tiled mosaic 20 days wide by 18 days tall, showing 360 days of sky all at once. The images are arranged chronologically, and are synchronized by time of day, beginning before summer sunrise. Time is compressed in playback at 24 frames/second so that each second represents 4 minutes of time.

This is still a work still in progress: As the camera on the Exploratorium roof continues to collect images of the sky, they will be integrated into the daily montage. Therefore the video will vary from day to day, always displaying the most recent 365 days.

Visit for more information. Below is his video. It’s best played in full-screen HD resolution. Click the middle arrow to start, then click the bottom right frame box.