Looking Up: At The Shadow The Time Will Be...

Jun 25, 2018

Credit by oksmith; A public domain image uploaded to https://commons.wikimedia.org by user AzaToth / Creative Commons Open Clipart

This week on Looking Up Bruce Bookout sheds some light and some shadow on the origins of the sundial.

As we have discussed before, timekeeping is an essential part of Astronomy.  The ancients relied on very low tech for many methods to tell time.  One effective method divides the day into relevant parts. Let’s shine a little light on the Sundial.

A sundial is a device that utilizes a spot of light or a shadow cast by the sun to measure time.  As the Earth spins beneath it, the Sun appears to cross the sky from east to west. As the Sun rises in Altitude, it changes in Azimuth, which changes the position of  a shadow cast by an object.  On a sundial, this shadow caster is called a gnomon. The area that the shadow, or point of light, is cast upon is called the dial.  By breaking the dial up into separate sections we can mark out different times of the day.  How cultures did this was determined by their sense of time. Sundials were used as both timekeeper and navigation device.

The earliest sundials date back to 1500 BCE in ancient Babylon.  Sundials were invented independently in every major culture around the world and became more sophisticated as the culture became more technological.

The modern world does not require their use, but they are retained for their aesthetic appeal, literary metaphor and mathematic studies.  Sundials are more common than you know, and remember only the shadow knows!

If you’d like to take a closer look at Sundials, or any of the other wonderful and amazing things in the sky, please visit csastro.org for a link to information on our monthly meetings and our free public star parties.