Safety First
This is an outdoor activity and you will spend some time exposed to the sun. Therefore, implement the current measures like applying sunscreen and wearing sunglasses, hat and long sleeve shirt. Please be cautious when handling sharp objects and tools.
1) Print or copy the Scouts go Solar Diptych Sundial model on paper. For sturdiness, consider pasting it on cardboard.
2) Carefully cut along the outer and pointed lines, following the instructions to create the sundial's shape
3) To customise the sundial to your location, find your latitude using an Atlas or online resources.
4) Mark lines on each side of the sundial's base corresponding to your latitude and hemisphere (from 0° to 45° North or South, you draw lines on all four side flips, from 45° upwards there are two lines to be drawn). Extend the lines to the border of the paper.
5) Fold the side flips downwards by 90°. All folds are easier to realise if bend over the edge of a metal ruler.
6) Fold the paper upwards along the horizontal central line by 90°.
7) Fold the paper downwards along the lines you drew corresponding to your latitude.
8) Correct all folds until they have an angle of 90°.
9) Create small holes where all the hour lines meet at the top and bottom of the sundial.
10) Tie a string through those holes. The shadow cast by the string will act as the sundial's pointer and tell the time. Install the string in a way that the sundial has a 90° bend in its centre.
11) We suggest to glue your sundial on the paper square which serves as base. Cut the excess length after glueing.
10) For the sundial to function, find a place where the pointer (the string) casts a shadow.
11) The sundial must face the North-South direction during the day. Its portability allows you to carry it around and experiment with different locations. Below, we show you three different methods how you can position your sundial correctly.
TIME CORRECTION: Every sundial does show ‘solar time’ for your location. There are up to three corrections to apply, if you want to know ‘local time’, i.e. the time a watch shows where you live. The first correction has to be applied, the second is optional and the third is interesting if you study the physics behind a sundial. (You find some more information how to take into account corrections 2 and 3 in the paragraph ‘Relevant information if you are facilitating’)
1. A sundial does not differentiate between “standard time” and “daylight-saving time”, in case this applies for your country. If you are on “daylight-saving time”, you will have to add one hour to the time that the sundial shows.
2. ‘Local time’ corresponds to your time zone which takes the time of one defined longitude. According how far East or West you are as compared to this line, the time shown on the sundial must be corrected up to more than one hour.
3. There is one more correction of up to plus or minus 15 minutes – called ‘Equation of Time’ – due to astronomical details of the path of the earth around the sun. This is only related to the day of the year, not to the location.
Instructional Guide: How to Orient Your Sundial for Accurate Timekeeping
Step 1: Placing the Sundial
To ensure your sundial functions accurately, it must be positioned in the right direction, where the pointer (also known as the winding) casts a shadow. The ideal placement is in the North-South direction during the day, allowing you to carry it around for exploration.
Step 2: Three Methods to Orient Your Sundial
(Text credit to Dr. Randall Brooks, National Museum of Science and Technology, Ottawa, Canada)
Method 1: Purist’s Method (for the northern hemisphere only)
- At night, locate the pole star, also known as the north star, in the sky. You can find it at the end of the Ursa Minor constellation and it’s normally the brightest star you see. This star marks the direction of the North.
- To orient your sundial, position the hand or winding of the sundial within 1º of the north celestial pole, which aligns with the pole star.
- If you find the pole star at the end of the Ursa Minor constellation, point the hand of your sundial towards the pole star for accurate orientation. For future reference, mark a slight reference point on a window or remember a landmark to preserve the device's orientation.
- Please note that this method is not applicable in the southern hemisphere since no star can help us perform this exercise.
Method 2: Practical Method (Using a Magnetic Compass)
- A magnetic compass can help determine the North/South line for orientation.
- However, be aware that there might be a difference between magnetic North and true North. Depending on your location, this difference can result in an hour or more reading variation.
- Use this method cautiously, especially in regions with significant differences between magnetic North and true North, such as southern latitudes.
Method 3: Easy Method (Using a Watch)
- As a simple approximation, you can use a watch (or the time of your cell phone) at any time to find the orientation.
- Position the sundial so that the shadow of the string shows the correct time on the watch. Do not change the position anymore.
- Remember that leaving the sundial in this position can lead to an error of up to 30 minutes throughout the year due to the equation of time.
- Orienting the sundial on April 15, June 10, September 1, or December 20 will result in an insignificant error.
- If you are using your sundial during a period of ‘daylight saving time’, position it so that is shows ‘winter time’, i.e. one hour earlier that the time of your watch. Remember to add one hour to all time readings.
Theory:
The earth rotates once about its own axis within 24 hours. As a result, we experience ‚day’ when our side of the earth faces the sun and ‚night’ when it faces away from it.
The day begins with the first rays of sun that appear on the horizon. The sun then seems to traverse the sky on a big arc, reaching the highest point at noon and slowly descending until it disappears below the horizon in the evening. This is the course of the sun. The sun rises in the East, descending in the West.
With the help of a sundial, one can use the course of the sun to measure time. Stick a pole into the ground and you can watch its shadow wander in the opposite direction of the sun throughout the day. As the axis of the earth is slightly inclined, the angle of the sunlight changes during the year. As a result, more or less sunlight is reaching the surface of the earth, causing the seasons. This inclination and the changing angle of the sunlight is also the reason why a stick in the ground can show you the movement of the shadow, but it needs some time corrections to precisely indicate the time .
Did You Know
Sundials were one of the earliest timekeeping devices used by humans, dating back around 4 thousand years ago in Egypt.
In the southern hemisphere, sundials are inverted and point South!
Evaluation
How accurate was the time reading in your experiment, as compared to the local time on a watch? If you see a difference: What correction factors did you not take into account, how precise was your orientation and the angle of the string?
Reflect on the activity and determine in which cardinal direction (North, South, East, West) the central vertical line on the sundial should point to indicate the correct time.
Reflection Questions:
What would happen if the axis of the earth would be in a right angle to the sun and not inclined like it is in reality?
Would the same system also work at night, with the moonlight? Why yes, why not?
