We all know that sundials are simply time-measuring devices that were created and used in ancient times in order to correctly determine the time of the day. They are known to be one of the oldest as well as the most natural method of telling the time. However, have you ever wondered how exactly did these fascinating devices work? Or perhaps, what kinds and types of sundials were there back in the day?
Sundials may have started out as fairly simple instruments for telling time, but over the years, they have adopted a certain level of complexity. Their primary function entirely depends on the movement of the sun.
Interestingly, it is assumed that the oldest type of sundial was probably a pre-historical man observing how his shadow shortened and lengthened during the day. After all, anything that has the ability to mark the passage of the sun during the bright hours of the day can be called a sundial!
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The first-ever sundial known to humankind was built around 1500 BCE in Egypt. It was an Egyptian shadow clock made from greenschist. This ancient sundial was shaped like an ‘L’ and it indicated the correct time with the help of vertical leg – a cross piece along the horizontal leg that basically cast the shadow.
This sundial was followed by what was called the ‘hemispherical sundial.’ It was designed in 280 BCE by Aristarchus of Samos, who was a Greek astronomer. The device consisted of a hemispherical opening that was carved into a block of either stone or wood.
A pointer or style was fixed at the center of the hemisphere and this style basically cast the shadow. The tip of this shadow would create a shadow arc on the hemisphere’s surface, and that is what helped determine the right time.
The Egyptians once created a T-shaped sundial that consisted of a vertical stick and a crossbar. There were five hours mentioned on the vertical stick, and it was positioned according to the time of the day. For instance, the stick was placed towards the East side during morning time, and then it was shifted to the west in the afternoon.
These sundials helped specify the time by casting light or shadow on the plate of the device. This plate is usually flat, but it can also adopt other shapes such as conical, spherical and cylindrical. The face of this plate has markings on it which mainly help display the correct time. Many sundials also had multiple markings that even helped calculate the dates along with the time. Later, more advanced and upgraded versions of sundials comprised of unique settings which allowed people to change the dates on the dial in order to calculate the correct time.
The underlying premise behind the working of any sundial has to do with the movement of the sun. The earth simply rotates on its axis while it revolves around the sun, and it does so in an elliptical orbit. This simply suggests that when the sun moves faster across a sundial when it is closer to the earth. It is also vital to mention here that the earth’s equator doesn’t align its rotation or orbital path around the sun.
This created some complications during the inception of sundials because they had to be redesigned in order to accommodate the differences and variances in the earth’s equator. Two major difficulties encountered when using sundials also had to do with the latitude and longitude.
In terms of latitude, problems were created when the sundial was used to measure a different kind of latitude than the one it was actually set up for. On the other hand, the longitude aspect required sundials to be set up in a way that meant that they were perfectly parallel with the axis of the planet. Both these factors had to be in-line in for the sundial to function properly.
The first-ever sundial that was created was naturally a very simple model with functions that were easy to understand. Later, however, as people started to realize and understand the intricacies of time and the sun, better and more efficient types of sundials were created in order to correctly determine the right time on any given day.
All these types had different layouts, such as arcs, lines, and texts that helped provide information on so many things such as the solar time, the sun’s declination, the hour of another city, and civil time, to name a few.
In order to properly understand the working of a sundial, it is essential to first comprehend the numerous factors associated with it.
This has to do with the sun and is directly determined by the position of the sun. Sundials have a noon line on them that is linked to the sun’s culmination. The noon line is always present in the North-South plain, and regardless of its orientation, you will always find it to be vertical on a vertical sundial.
As the name suggests, these are lines on a sundial that meet each other at the same point. This is defined as the point where the sundial is attached to its polar style, but with one exception, and that is when the point is rejected to infinity.
Ancient sundials often made use of markers in order to determine sunset and sunrise patterns. These markers often represented unequal hours, which basically refer to the differences in the number of hours between sunrise and sunset depending on the day and the moment of the year.
It is a common fact that the altitude of the sun varies according to a particular moment of any given year. This is the main reason why the shadow that is cast on the sundial varies in length and ranges between short and long. These differing lengths are basically what helped calculate particular instances of the sun’s declination.
Types of Sundials
There are two major types of sundials, each of which is broken down into further categories. The two main groups of sundials are: Azimuth Dials and Altitude Dials.
1. Azimuth Dials
Azimuth is defined as an angular measurement in a spherical coordinate system. This angular distance or measurement is basically the direction of a celestial object from the point of the observer. Azimuth sundials help determine the time from the sun’s angle on its daily arc. In other words, they indicate the time by using the sun’s direction to do so.
There are different types of Azimuth dials that tell the time with the help of the hour angle of the sun.
This is one of the most commonly found types of sundials and is largely characterized by its prominent flat-shaped dial plate. It is usually seen on pedestals in gardens, which is why it is also often referred to as a ‘garden sundial’. The main reason for its commonness is that it has the ability to tell the time whenever the sun is shining, primarily because the dial plate lies flat on the ground in a horizontal manner.
The Horizontal Sundial has three main parts: the gnomon, the hour markers, and the faceplate. The gnomon is the vertical part of the sundial that casts a shadow in order to tell time; the hour markers show the time on which the shadow lies, and the faceplate is that area of the dial where the shadow is cast, and that tells the exact, final time.
Although these parts of the sundial can be made with any material, the most commonly used material is wood since it remains weatherproof and rigid.
The horizontal dial plate of this sundial consists of hour lines that radiate outward from the very top of the gnomon. The key to using horizontal sundials is that they should be adjusted for various latitudes. Most of these Dials usually have their gnomon usually set at 45 degrees, which obviously suggests that the sundial is designed to be used at a latitude of 45 degrees.
This type of sundial is popularly found hanging on the walls of churches and other similar buildings. The shadow-receiving plane of the vertical sundial is aligned vertically and the gnomon is positioned in a way that it aligns with the Earth’s axis of rotation. A key feature of this type of sundial is that it is not equiangular, which means that the line of shadow does not move in a uniform manner on the dial’s face.
Vertical sundials are typically mounted walls on numerous buildings such as church-towers, town halls, and cupolas. The main reason for mounting them on walls is that they can be easily spotted from far away. They may even be placed on all the sides of a regular tower. This way, the dials can allow people to tell the time throughout the day. The gnomon of these sundials is often a single metal bar, but may also be a tripod of metal bars in order to help provide rigidity. Considering the fact that the gnomon’s style should always be parallel to the Earth’s axis, it is usually pointing toward the true North, and its horizontal angle is the same as the geographical location of the sundial.
If the vertical sundial faces due south, the gnomon lies at an equal angle to the co-latitude of the wall or the place where the sundial has been mounted.
In this sundial, the dial plate is set along the East-West direction in an inclining position, which makes it parallel to the polar axis. Its gnomon is also parallel to the dial plate, and so are the hour lines with each other.
This particular positioning of the polar sundial makes its shadow slide sideways on top of the surface as it eventually moves in a perpendicular direction when the sun rotates. When the sun’s rays are parallel to the plane of the dial, the parallel hour lines end up spacing far apart, and the shadow moves very quickly.
One of the key requirements of a polar sundial is that its face should be parallel to the gnomon and it doesn’t necessarily have to be vertical.
This sundial has its table in the polar plane that forms an equal angle to the local altitude while being inclined with the ground. The style of the polar sundial is usually installed on a rod or may even be made of a rectangular plate.
Also known as the ‘equinoctial dial,’ the Equatorial sundial has a unique feature which is its ‘planar surface’ that receives the shadow. The shadow that is cast is exactly perpendicular to the gnomon’s style.
The reason why the Equatorial sundial is called by this name is because it is parallel to the equator of the celestial sphere as well as that of the Earth. It is believed to be one of the easiest sundials to construct and visualize. All it consists of is a flat surface that is aligned with the celestial equator along with a gnomon that is perpendicular to the same celestial equator.
The dial plate of this sundial is often a flat plate or sometimes even a circular ring. The plane of this ring lies perpendicular to the gnomon. Since the gnomon of the equatorial sundial is parallel to the Earth’s axial rotation, the dial plate is also parallel to the plane of the equator.
A popular sub-type of this sundial is the equatorial ring sundial, in which the hour markings are contained within a ring or partial ring in place of the solid plate surface. When the sun travels along the equator plane at the equinox, the top half of the equatorial ring casts a shadow which completely covers the sundial markings. This is why this type of sundial is unable to tell the time near the equinox.
2. Altitude Dials
This is the second main sundial group, and as the name suggests, it helps determine the time by using the sun’s altitude. The altitude of the sun is basically its height above the horizon. These Dials were often incorporated in folding rules and quadrants.
Altitude dials are not oriented towards the north, but in fact, they are generally held vertically towards the sun. A spot of light the shadow tip of the dial’s gnomon is what usually indicates the sun’s elevation.
This is also called the vertical center dial and is a type of horizontal sundial, but with a vertical gnomon. The hour markers of this sundial are positioned in an elliptical manner. An interesting feature of the Analemmatic sundial is that its gnomon does not hold a fixed position and is required to change daily in order to determine the time of the day as correctly as possible. This is the main reason why there are no lines on this type of dial and the time can only be read on the ellipse.
The movable gnomon of this sundial is vertical, and its position on the dial actually depends on the date, which is what determines its variable center. The circumference of the dial’s ellipse has points on it which indicate the total hours of the time.
There are three main defining features of the Analemmatic sundial, which include the size of the ellipse that is decided by the designer, the declination of the sun, and the latitude of its location. The sun’s declination helps determine the daily gnomon position while its location’s latitude identifies the position of the hour markers on the ellipse.
The reason why this sundial is ellipse is because it uses a vertical gnomon and its short-axis is aligned to the North-South while the long axis is more toward the East-West.
As the name implies, the Digital sundial is quite an updated and a fairly recent invention. This type of sundial displays time in digits and sometimes even in the form of words and pictures.
The digital sundial has been described as a ‘singular blend of utility and artistry’ since it offers a creative combination of the advancements of modern technology along with the ancient science of sundials. It works in a manner that is similar to the function of a digital clock, as both of them display the time with the help of digits.
This sundial uses two closely spaced parallel masks that display different images. The image projection completely depends on the angular position of the sun. The first mask basically casts a light pattern that is often striped. The light is cast on the second mask, and this simply depends on the height of the sun. On the other hand, the second parallel mask contains narrow stripes of digits that are displayed afterward.
Interestingly, the striped patterns of the first mask light up the same stripes of the second mask. Both of these together greatly match the image that later represents the actual current time.
As fascinating as digital sundials sound, they do come with a few limitations. They don’t work at night and can only tell the time in 20-minute intervals. This suggests that it may not tell you the correct time all the time.
Contrary to other types of sundials, the Ring sundial makes use of light to tell time instead of using shadows. It has a ring with hour lines marked towards the inside. These hour lines consist of a tiny hole, through which sunlight falls on the ring. A key factor is that the ring should be turned on in order for the light to fall on the correct dateline.
The earlier types of ring sundials used to be very small, with a diameter of less than 25 mm. This small size made it very difficult for people to read and correctly identify the time displayed on the dial. Soon enough, people realized that they needed bigger models of this sundial and they saw no reason against increasing the size. The ring sundials that came later were as big as 10cm in diameter, which made telling the time really easy.
This sundial is also known by many other names, such as pole sundial, pillar sundial, portable cylinder, and shepherd’s dials. It was once also called a traveler’s dial primarily because, back in the day, shepherds used to carry it in their pockets.
A cylindrical sundial is shaped liked a cylinder with the gnomon attached or positioned on its movable top. The main body of the cylinder has hour lines printed on it, and these lines are basically in the form of inscribed curves.
The main principle behind the cylindrical sundial is that the sun reaches a different height according to the hours of a given day and the days of a given year. This sundial seeks to measure the sun’s height by using the gnomon to cast a shadow. This shade represents the correct hour of the time by corresponding with the given height of the sun.
The dial of the cylindrical sundial is contained in a diagram that has a lot of divisions. There is a vertical division that that indicates the time and a horizontal one that displays days and months of a year.
In order to determine the correct time, the gnomon of the sundial is set over a vertical line of the day. The time is shown exactly where the shadow of the tip of the gnomon falls on any of the hour lines. An important thing to remember is that this cylindrical sundial is able to tell the correct time only at the latitude for which the dials have actually been adjusted and prepared.
Sundials have certainly come a long way, especially considering the stark difference between the first-ever sundial and the versions that were produced later. It is equally fascinating how they use the sun’s position to determine the correct time. Imagine, if it weren’t for the clocks and watches we have today, we would also be waiting on these sundials to tell us the current time!