You know it, you find yourself in nature or in a place without the conveniences of modern times. But what to do if you forget your watch and your phone battery is dead? That's why it's worth knowing a few tricks and tips for telling time using the Sun, which will help you cope anywhere in any situation. If you think that sundials are an invention of the past that has no use nowadays, you are mistaken. Let's talk more about sundials, their history, and how to use them in practice.
What is a sundial
A sundial is a device that measures time according to the position of the Sun. In common designs such as horizontal sundials, the Sun casts a shadow from a gnomon, which is a thin rod with a straight edge, onto a flat surface marked with lines indicating the hours of the day. The shadow cast by the tip of the gnomon is always the solar time. As the Sun moves across the sky, the shadow of the gnomon's edge gradually aligns with different hour lines on the dial. Such designs rely on a gnomon that is aligned with the Earth's axis of rotation.
So, if such a sundial is to show the correct time, the gnomon must point to true north, and the angle of the gnomon with the horizontal plane must equal the latitude where the sundial is located. Essentially any form of a stick - known as a gnomon - that casts a shadow can be considered a sundial. The position of the shadow can then be used to determine the current solar time.
Types of sundials
Below, we bring you an outline of the main types of sundials. This is therefore not a complete list.
Horizontal
This is what most people imagine when they think of a sundial: a horizontal dial with an angled gnomon, set in a beautiful English garden.
Vertical
Vertical sundials are often attached to the side of a building. Historically, many were placed on churches. In medieval Britain, sundials were literally carved into the walls of churches, likely to display the hours of church services.
Equatorial
These sundials have a dial that is tilted at an angle parallel to the equator. The gnomon is then set at a right angle to the dial plate, parallel to the Earth's axis. This is another way to solve certain quirks of space-time caused by the tilt of the Earth's axis.
Armillary
A type of equatorial dial. In ancient times, armillary spheres were used to demonstrate the workings of the solar system.
Analemma
This unusual type of sundial does not show time, only the date. It works in such a way that if you were to mark the position of the sun in the sky at, say, noon every day for a year, you would trace out a figure eight. The analemma shows this figure-eight pattern marked with dates.
How to make a sundial
To test the usefulness and charm of a sundial for yourself, we bring you a simple guide on how to make one. To make a simple sundial you will need:
- A straight stick
- 12 pebbles or seashells
- Markers - for marking the numbers
- A place with constant sunlight
Procedure:
Step 1
Find a sunny spot (preferably in the garden) where you can build your clock. You will probably need a circular area with a diameter of 25-30 cm.
Step 2
Write numbers from 1 to 12 on the stones of your sundial.
Step 3
Place one end of a stick into the ground so that the opposite end points toward the sky. The stick serves as the gnomon of the sundial and will cast a shadow. Over the next few hours, you will need to watch the shadow of the stick to see if it needs to be tilted. When the sun is directly overhead at 12:00, you want the shadow of your stick to be as short as possible.
Step 4
When you find the shortest shadow, place a marker for the 12:00 hour at that spot. Then arrange the remaining stones to complete the sundial. Alternatively, you can use an actual clock to mark the hours. For example, when your clock shows „9 a.m.“, place a marker at the end of the shadow and label it with the number 9.
Step 5
Check the shadow of the gnomon to determine how far apart your stones need to be. In theory, each stone should be the same distance from the gnomon (at the center of your circle), but this will depend on the length of the shadow cast by your stick and the area where you install your sundial.
Step 6
Set the clock by placing stones where the shadow falls each hour. Once the stones are in place, check the sundial the following day at various times to see how your clock works.
Sometimes you will need to adjust a few stones so that your sundial is accurate at showing the time during the morning and early afternoon hours. However, you must not forget that a sundial is not really a perfect circle – if you were able to track the movement of light/shadow for a full twelve hours or more, you would see that the hour markers get closer together as the day progresses.
How it was in the past
Already in the distant past, people felt the need to know the time of day. This was especially true of the great advanced civilizations in the Middle East and North Africa, when clock production began approximately 5000 to 6000 years ago. With their accompanying bureaucracies and religions, these cultures found a way to organize their time effectively. The Egyptians were among the first to formally divide their days into parts resembling hours. They created so-called obelisks, which were slender, tapering four-sided monuments. Their moving shadows formed a kind of primitive sundial, which helped citizens divide the day into two parts by indicating noon. Obelisks also made it possible to show the longest and shortest days of the year. Later, however, markers were added around the base of the obelisk to indicate further time divisions.
Another Egyptian sundial began to be used around 1500 BC to measure the passage of hours. This sundial divided the sunlit day into ten parts plus two „hours of twilight“, in the morning and evening. When a long stem with five variably spaced markers was oriented east and west in the morning, a raised bar at the eastern end cast a moving shadow onto the markers. The device was turned in the opposite direction at noon to measure the afternoon hours.
In an effort to achieve greater year-round accuracy, sundials evolved from flat horizontal or vertical plates into more elaborate forms. One version was the hemispherical dial, a bowl-shaped depression carved into a block of stone, which carried a central vertical gnomon or pointer and was marked with sets of hour lines. The hemicycle, said to have been invented around 300 BC, removed the unnecessary half of the hemisphere to create a half-bowl appearance carved into the edge of a square block. By 30 BC, the Roman architect Marcus Vitruvius was able to describe 13 different styles of sundials used in Greece, Asia Minor, and Italy.
The Romans also built precise sundials in order to determine the time. An interesting custom, symbolic of Roman power, was the transporting of ancient Egyptian obelisks to Rome and placing them as sundials in public places. However, much of the expertise in sundials was lost during the Dark Ages. When sundials reappeared, they were less sophisticated, with incorrectly angled gnomons, and often marked the times of religious services rather than what we consider to be true time. The Arabs rediscovered the method of making accurate sundials in the late Middle Ages, and this knowledge somehow made its way back to the West.
Sundials are one of the oldest known scientific instruments used for measuring time. Their basic idea was to create a space that offers an opportunity for reflection. Reflection on time, observing its passage in connection with the apparent movement of the Sun across the sky, and reflection on oneself. Perhaps on the fact that time can be used effectively, but it can also be wasted.
