Ancient SUNDIAL Clock

Hello everyone!

In this instructable we will learn how people of ancient times measured time and will discuss how to make one and what are the consideration, corrections and all.

Before the invention of clocks and watches sundials were used to tell times. The first sundials were used more than 3,500 years ago in Egypt.

It's hard to tell the era from which clocks are being used. As the archaeological records, in ancient times Shadow clocks were used, after then with the help of Egyptian astronomy and Babylonian astronomy we developed new clocks to use.

So, a Sundial is a device or you can say its an instrument that tell us the time of day. It consists of a flat plate (the dial) and a Gnomon, which casts a shadow onto the dial. As the Sun moves across the sky, the shadow aligns with different hour-lines, indicating the time of day.

There are several different types of sundials. Some sundials use a shadow or the edge of a shadow while others use a line or spot of light to indicate the time. In our case we will make a Horizontal Sundial.

Sundials only indicate the local solar time, to obtain the national clock time, corrections are required.

There are lots of variety of sundials, history and many more things to learn. So, i recommend you want to read more about Sundials from the sundial wiki page to understand better.

Also i want to thank Mr. Jill Vincent to help with his pdf, this will help you to understand the time corrections better. I will also attach it below if link doesn't work.

Let us imagine the Earth as a giant sundial. The Earth’s axis is tilted at an angle of 23.5° to the plane (as figure 2.1) of its orbit around the Sun. As the Earth rotates on its axis, the shadow of a vertical stick at the pole would form a circle on the surface of the Earth parallel to the equator. If the circle is divided into 24 equal hour marks, the position of the shadow around the circle would give the time. Sundials based on this principle are called equatorial sundials.

So, in 24 hour earth rotates 360 degree or in 1 hour earth rotates 15 degree.

For a sundial, the gnomon must be parallel to the Earth’s axis and it should be at an angle equal to the Latitude of the place and the height of the gnomon = 5/12th of the outer radius of the dial.

The Sun changes its position on the celestial sphere, being - on north hemisphere - at a positive declination in spring and summer, and at a negative declination in autumn and winter.

This model of the Sun's motion helps to understand sundials. If the shadow-casting gnomon is aligned with the celestial poles, its shadow will revolve at a constant rate, and this rotation will not change with the seasons. This is the most common design. In such cases, the same hour lines may be used throughout the year. The hour-lines will be spaced uniformly if the surface receiving the shadow is either perpendicular or circular about the gnomon.

The chief advantages of the horizontal sundial are that it is easy to read, and the sunlight lights the face throughout the year. All the hour-lines intersect at the point where the gnomon's style crosses the horizontal plane. Since the style is aligned with the Earth's rotational axis, the style points true North and its angle with the horizontal equals the sundial's geographical latitude L.

In the horizontal sundial (also called a garden sundial), the plane that receives the shadow is aligned horizontally. Hence, the line of shadow does not rotate uniformly on the dial face, rather the hour lines are spaced according to the rule,

tan H = sin L tan (15 x t)

where L is the sundial's geographical latitude (and the angle the gnomon makes with the dial plate), H is the angle between a given hour-line and the noon hour-line (which always points towards true North) on the plane, and t is the number of hours before or after noon.

As figure 3.1 :

For a horizontal sundial, the circular equatorial dial is projected onto a horizontal plane as an ellipse ( as shown in figure 3.1 ). As the gnomon makes an angle L with the horizontal. The semi-minor (east–west) axis is a, the radius of the equatorial dial. If b is the semi-major (north–south) axis of the ellipse.

Sin L = a/b

b = a/Sin L

In Figure: 4.1, angle T is the hour angle measured from the north–south line around the equatorial dial. Angle H is the projected hour angle on the ellipse of the horizontal dial. Using the same approach as for the vertical sundial, the parametric equations for the ellipse for the horizontal sundial are,

x = a sinT

y = a cosT / sinL

Therefore, the hour angles are given by

H = tan–1 (tanT sinL)

The hour angles, H for a horizontal sundial in Assam are shown in Table 4.2. The latitude 26.02° has been used.

For 11 am, for example, H = tan–1(tan15°sin26.02°) ≈ 6.7°.

For horizontal sundial in northern hemisphere, the numbers will be clockwise and anticlockwise for the southern hemisphere. Figure: 4.3 shows the spacing of the hour angles for the horizontal sundial for Assam.

The correction of time is major part in Sundials. It differs from dial to dial, but the reading of an old sundial should be corrected by applying the present-day equation of time.

The most common reason for a sundial to differ greatly from clock time is that the sundial has not been oriented correctly or its hour lines have not been drawn correctly.

Reference has been made already to the need for correcting sundial time for the local longitude if that differs from the longitude on which local time is based. Sundial time also needs to be adjusted slightly for two further reasons:

• The Earth’s path as it revolves around the Sun is an ellipse, rather than a circle and the Sun is not quite at the center of the ellipse.

• the Earth’s axis is tilted at an angle of 23.5° to the plane of the elliptical orbit.

In hypothetical word we can say that the earth rotates around the Sun at a constant speed throughout the year as out watch clock time.

Summer (daylight saving) time correction

Some areas of the world practice daylight saving time, which changes the official time, usually by one hour. This shift must be added to the sundial's time to make it agree with the official time.

Time-zone (longitude) correction

A standard time zone covers roughly 15° of longitude, so any point within that zone which is not on the reference longitude (generally a multiple of 15°) will experience a difference from standard time equal to 4 minutes of time per degree. For illustration, sunsets and sunrises are at a much later "official" time at the western edge of a time-zone, compared to sunrise and sunset times at the eastern edge.

For this say earth rotates at 360 degree at 24 hour.

Let's say,

360° = 24 hour

15° = 1 hour

15° = 60 min

1° = 4 min

But in reality, earth does not move at constant speed throughout the year. Its speed varies from summer to winter. In summer Sun gets up and in winter the Sun get lower.

Equation of time correction

Although the Sun appears to rotate uniformly about the Earth, in reality this motion is not perfectly uniform. This is due to the eccentricity of the Earth's orbit (the fact that the Earth's orbit about the Sun is not perfectly circular, but slightly elliptical) and the tilt (obliquity) of the Earth's rotational axis relative to the plane of its orbit. Therefore, sundial time varies from standard clock time.

Next is our North adjustment. As in the beginning i told that our sundial should orient with the True North. But, as our compass shows the magnetic north. So in reality our magnetic north and our true north differs from location to location and we can see a distance between our magnetic north and our true north. This distance can be calculated by the angle they make with each other, this angle is called the Magnetic Declination. You can find the magnetic declination of your place from this website called magnetic-declination.com.

So now we will calculate time correction with the help of Equation of time. From this website you can get the time correction of your current date and year.

Correction :

Here, 360° = 24 hour, 1° = 4 min

As on 21st May 2021,

Noon = 12 - [ Longitude - Timezone x 15° each ] x 4 min

= 11:60 - [ 89.97 - (+5.30) x 15 ] x 4

= 11:60 - [ 89.97 - 79.5 ] x 4

= 11:60 - [ 10.47 x 4 ]

= 11:60 - [ 41.88 ] - (+3.2)

= 11: [ 60 - 41.88 -3.2 ]

~ 11:15 am

A sundial can be achieved with few simpler tools and materials. Our sundial is a simple one, its a horizontal sundial. Here we made our main dial plate with 12 mm plywood and our gnomon is made with 2 mm ply. For other parts like, hour numbers I used PVC sheet and plastic sheets for decorating like borders. For hour and minute marks I used Aluminium, copper and golden wires. Direction compass & N-S-E-W are made with aluminium and some color pencil and solid colors being used.

The making process is very simpler, I only designed it so it may look complex but, if you go through the pictures of each step it will clear all your doubts.

So, below are some tools and materials that I used during the process of making our sundial,

Our Tools :

1. Jigsaw
2. Hacksaw
3. Knife
4. Scissor
5. Plier
6. Scale
7. Angle protractor
8. Pencil
9. Rubber
10. Sketch pen
11. Compass
12. Scientific calculator

Our Materials :

1. Plywood ( 12mm, 2mm )
2. PVC sheet
3. Plastic sheet
4. Aluminium sheet
5. Sand paper
6. Copper wire
7. Aluminium wire
8. Golden craft wire
9. Fevicol wood glue
10. Super glue

Color & Finishes :

1. Golden
2. Silver
3. Black
4. Varnish
5. Glitter pen ( silver, orange )
6. Permanent markers ( red, blue, black )
7. Brushes

I made the dial plate using a 12 mm plywood. I took about 6 inch radius circle and cut it with the help of my jigsaw. Then I sand it and made it smooth plane to be ready for my dial plate.

Here I use different diameters as our design pattern and marked roughly with a pencil to help in future to set our designs.

I also added Hour lines with our calculated hour angles that we calculated previously and made some designs.

Here I used a compass design to show the directions of the sundial. I used plastic sheet as the ring and aluminium sheet as compass needle and for direction marks N-S-E-W.

I made this plastic sheet at my home from a old paint bucket, if you want to check the video click here.

Next I cut some plastic sheet and made few thin strips and then attached to my design marks. Also I glued every design elements here.

As I already marked hour and minute marks, So, now I used my PVC sheet and cut thin strips for making my hour marks, as they should be bold. Then for other minute marks I used aluminium, copper and golden craft wires.

I made this PVC sheet at my home from a PVC pipe, if you want to check the video click here.

Like hour and minute marks, I added some compass marks here too. I used aluminium and copper wires to give my markings.

Here I used Silver as the border and strips and Golden for my hour area, Then I finished the plate with Varnish as a coat.

Finally, I colored my compass with color marker pens. Now it gives a good contrast.

For making my hour numbers I used Roman numbering. Here I again used my PVC sheet. First I marked all my number ( I, V, X ) and then I cut them using my cutter. After that I sanded them to finish the edges.

Again, I made this PVC sheet at my home from a PVC pipe, if you want to check the video click here.

I used my Black marker pen to color the hour numbers and then using fevicol wood glue I attached every number to its position.

This is the main component of our dial. The gnomon should be at an angle of 26 degree ( or the Latitude of the place ).

Here I used my 2 mm plywood piece and made a random design on it. Then I cut using my mini hacksaw and curving tools and then sanded it nicely. Here our Gnomon is now ready.

Lastly I finishes my gnomon with a coat of Varnish and painted the edges with Silver color. Now it looks perfect.

Then I finally fixed the gnomon parallel to earths axis and perpendicular to the Dial plate with the help of wood glue.

And here our mostly awaited Sundial is ready to use. Now put it on ground by aligning it to the North direction and the shadow the Gnomon creates will give us the time of the day. Don't forget apply the correction of time.

So, Thank you everyone !

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