How Does a Sundial Work?

The sundial is responsible for telling us what time of the day it is. Basically, the sun casts a shadow on a triangular pointer called a gnomon. This is pronounced like "no-men." The sundial looks like a clock with numbers all the way around it. The sun's shadow reveals the hour of the day. Each sundial must be made specifically for the region it is telling the time for as the sun shines differently around the globe.

Individuals that live in the south should have their sundial numbers closer together during the day time, but farther apart during night and early morning hours. Individuals in the north would have their sundial numbers closer together during morning and evening hours. The reason for this is the amount of time the sun is present each day in each location. It is important to note that the lines are not equally spaced around the sundial. It is important for you to look up your latitudes and get a sample sundial sheet if you want to create your own sundial.

Time zones also affect the placement of the numbers on a sundial. This figure is represented by your longitude reading. If you are not proficient in math, it is best to buy a sundial from someone who has already calculated the longitude and latitude of your area. They will have the numbers set up for you exactly where they need to be.

There are three main types of sundials--the horizontal dial, vertical south dial and the analemmatic dial. The horizontal dial is mounted parallel to the earth's surface and is the easiest of the three sundials to read. It can tell you the time from sun-up to sun-down. The vertical south dial is usually placed on a tree or outdoor object that is facing south. This sundial is attractive and unique which makes it the topic of many conversations. Finally, the analemmatic dial is placed parallel to the earth's surface like the horizontal sundial. The difference is that the gnomon is a rod that has to be moved each day. There is a hole for each day of the year and the rod must be transferred each day. It isn't as reliable as the other two dials and can be hard to read.

You may also want to add a secondary set of numbers to be displayed for daylight savings time. The sundial can not be automated so it would be very difficult to adjust it to tell the new time. If you add some numbers underneath, you will be able to correctly tell the time without having to get a whole new sundial.

Resources

• The Sundial Store