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Students will use fab lab tools to create a custom sundial for their area and learn how to mark it with important yearly events.
Tools:
Materials:
Safety Tips: Laser cutting can produce fires. Please use manufacture recommended and lab tested settings for your material. Have a fire extinguisher nearby. Laser cutting generates hazardous combustion products. Please use proper ventilation.
Follow all safety precautions on the spray paint can when painting. Use proper ventilation and wear respiratory protection. Do not paint eyes or skin.
Determine the difficulty level that your students need and that you have time and resources for.
This lesson can be greatly modified for your students and allotted time frame. You can design and make the stencils and/or gnomons before your students arrive to decrease the difficult and time requirements.
An example of a laser rastered sundial. It does have more precision than one made using spray paint and template but this took 23 minutes to raster whereas using the stencil takes several minutes and multiple stencils could be made.
Background information on sundials.
A sundial is a device that allows you to tell the solar time based on your location as the sun transitions through the sky. You can think of it as a shadow puppet turned into a clock. It is composed of a base with hour indicators and a gnomon which blocks the sun, casting the shadow on the base.
An image of a sundial being used on the Mars rover can be found here: https://apod.nasa.gov/apod/ap990428.html
A video of Bill Nye explaining sundials can be found here: https://www.youtube.com/watch?v=NWDlZ3j-m9g
A video of Bill Nye explaining why the Mars rover has a sundial can be found here: https://www.youtube.com/watch?v=F-Atrlz-cSI
We have to account for the geometry of the Earth to make a sundial work properly.
The Earth is a sphere, which rotates on an axis that is tilted by 23.5 degrees from perpendicular with the plane of orbit around the sun. The “middle” of the Earth is called the equator. A location’s distance from the equation is called its latitude and it is measured in degrees.
This matters for our sundial because the spacing between hours on our base will need to be adjusted to account for the angle we are at. We can use a sundial calculator to determine what angles our indicators should be. A good calculator that can help us create our template can be found here: https://www.blocklayer.com/sundial.aspx
Use the Find Latitude button to drop a pin on your location to find your latitude for the calculator.
If students will be designing their own stencils have them save the base and gnomon images the calculator creates. They can import these into the design software to aide in the creation process.
While the calculator creates a gnomon for us, it is important to know how it does it. It is creating a right triangle that has one leg that is the length of our base and the adjacent angle matches our angle of latitude. If your students are able to calculate the second leg based on those inputs, you can have them create their own gnomon. If they don’t have the required math knowledge you can have them explore a right triangle calculator: https://www.calculator.net/right-triangle-calculator.html
If you are going to speed the in class process up you will want to design a stencil that can be spray painted.
Design for a stencil.
Design for a freestanding gnomon. You can also just use a block attached to one or both sides of the gnomon.
Design for a laser rastered sundial. TN=True North (geographic north) and MN=Magnetic North.
The following instructions will help with the creation of a sundial base stencil. This can be created either partially or fully by the instructor ahead of time depending on students’ level and time allotted.
You can import the images created by the calculator and use them as a diagram or you can use the lengths and angles produced by the calculator depending on student ability.
There are a few things to keep in mind when creating a stencil designed to be used multiple times.
Now that the stencil is designed you can laser cut it. If you had students design their own sundial you would have them raster them here.
Laser cutting the stencil.
Laser cutting the stencil. I’ve labeled it as a stencil (top left) so that it is obvious it isn’t scrap material once it has paint all over it.
If you have not cut the stencils ahead of time, you can do so with students present. If students are present in the lab, it is a good idea to at demonstrate the cutting process even if you have pre-cut the stencils they will be using.
Use proper settings for your laser and your materials and ensure that proper safety procedures and discussed and utilized. Modeling good safety is one of the most important things you can teach.
If you are using stencils this is where you use them to paint your sundials.
Follow safety procedures when using spray paint. Not much paint is needed when using the stencil.
If the material you have available for bases are dark in color it is a good idea to have students apply a light colored base coat so that there is good contrast for shadows. This greatly improves readability of the sundial, especially when it is partially cloudy.
Have students select a dark color paint to spray on their stencils.
Have students place their stencils onto their sundial bases. Using appropriate safety measures, have students spray paint using their stencils. Instruct students that getting paint through the holes in the stencils is the goal and that not moving the stencil midway through the painting is the key. Remove the stencil after painting and give time for the paint to dry.
Students can paint their gnomons in any color or design they wish.
If you use stencils or have students design their own dial, they will all need a gnomon.
An example of using the block method for stabilizing the gnomon.
An example of using cutout connections to stabilize the gnomon.
How you construct a base for your gnomons can vary. I recommend a simple method of attaching two small wooden blocks to the base of the gnomon to give it feet. You could also have designed other methods when you created the stencils. You could also glue the base and the gnomon together but this is not a strong joint and is easily disconnected.
Remember, the base of the gnomon is the leg that is the same size as your base.
There are three types of north/south and the differences between them are important for sundials.
The compass is aimed at magnetic north.
If you are in the northern hemisphere, you will be concerned with north and if you are in the southern hemisphere, you will be concerned with south.
There are three different types of north/south.
Geographic north/south is the point located at the Earth’s axis
Magnetic north/south is the point a magnetic compass will point to and is based upon multiple factors with the largest being the Earth’s magnetic field. This usually does not align with geographic north/south.
Map north/south is the direction of up or down on a map. As a map is a two-dimensional representation of a three-dimensional sphere this usually does not align with geographic north/south.
Some maps provide indicators of how many degrees the three north/souths are off from each other.
The difference between magnetic north and geographic north is declination and we need it so that we can properly align the sundial.
Declination in the Anchorage, AK area is about 15 degrees so I’ve turned the dial that far off of magnetic north.
As our norths are not always the same, we have to have a way to compensate for the differences. That compensation is called Declination.
Declination is the angle between magnetic north and true north. This angle varies depending on your location.
You can read more about declination here: http://www.compassdude.com/compass-declination.php
As we will need our sundial’s noon position to point directly at geographic north, we will need to know the declination for our area. We can find this by using a magnetic field calculator. You can look up your latitude and longitude and then use them to find declination on the following page: https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml#declination
This is where you get to use a magnetic compass and the information you have about declination to align the sundial with geographic north.
Align the compass with your sundial and then turn it until the compass needle aligns with your declination mark.
Align the back end of the gnomon with the back end of the sundial.
If your sundial material is squared and your gnomon is parallel with the edge you can align the compass on the side of the material for aligning with geographic north.
Offset a magnetic compass by the declination you found for your area. Make sure you are a decent distance away from any buildings or large pieces of metal, including catches and rings. Use the compass to align your sundial with geographic north/south. You should be able to place the center of the compass on the noon line and have the arrow crossing north over the same noon line.
We have to assess our expectations for sundial accuracy and consistency. We are going to need a slight bit of interpretation to get our sundial time to align with what our clocks say.
Using a different timepiece, check the time on the sundial. Is it correct?
Odds are that your sundial won’t agree with your watch. If you have made multiple sundials they should all agree with each other if they were built and aligned properly.
One reason your dials will probably be off is that sundials don’t take daylight savings into account. A sundial tells the time based on the relationship between the sun and the Earth and someone forgot to send them the memo about implementing daylight savings time.
The other reasons are more complicated.
Each time zone covers a wide section of Earth. Alaska is in one time zone. A watch will tell us that the time is exactly the same in southeast Alaska as it is on the end of the Aleutian chain. However, on 7/15/2020, solar noon (the time when the sun is at its peak) will be in 1:03 PM in Juneau, AK while it won’t be until 3:34 PM on Attu Island, AK. Your location within your time zone will affect your sundial time.
A map of Alaska with Attu Island being at the bottom left and Juneau being near the bottom right. These two locations are 2,040 miles away from each other.
The Earth’s orbit also affects sundial accuracy. The orbit is actually an ellipse, which when combined with the Earth’s tilted axis, leads to an always changing solar day.
The great news is that all of these errors can be calculated! This allows us to still use our sundial to tell time that will align with our watch.
To create a listing of the correction needed for each day we are going to use an adjustment calculator. I recommend using http://www.solar-noon.com/
Type your location name in the location box. To find the latitude and longitude at your location you can use this website: https://www.latlong.net/
In the first latitude and longitude boxes you will put the numeric value that returns for your location. The second box will be for the letter of the direction. If your latitude returned a positive value use N. If your latitude returned a negative value, use S. If your longitude returned a positive value use E. If your longitude returned a negative value use W. If you receive an error telling you that your time zone is incorrect, use the GPS coordinates instead of the decimal values.
You can select if you’d like to create a list of when solar noon is each day which can be helpful for aligning your sundial if you do not have a magnetic compass.
Select “Standard Time Correction” for the type of calendar. This will give you a table with the correction values for each day of the year. This table does not take daylight savings into account so if you are in an area that uses it you will have to add an extra 60 minutes in during that time period.
Watch the shadow over a period of time. What direction does it move? Some historians believe that the direction of analogue clock movement is based on the direction the shadow moves on sundial, which created the term ‘clockwise.’
This is the cultural connection and how we can use our dial to track events.
Take a sundial into an area not lit by sunlight. Demonstrate with a light source how the length of the shadow will change throughout the year by raising the light (summer) and lowering the light (winter). Ask students how this could be used to mark important annual events such as salmon returning to a river, breaking of sea ice, or the first snow on the mountains.
An indicator can be placed at the end of the shadow (usually along the noon line but it can be anywhere) with a label for what the event is. With the exception of a solstice, the shadow will rest on each point twice during the year due to the cyclical nature of the seasons.
Have students brainstorm other events they might like to record on their sundial.
This project can be a leaping of point for many other ideas. Here are a few.