Drawing these is fun, and makes a good science education project for small or large kids (one's own, or a class at school). It should take a little over an hour to do the basic measurements and drawing, more if one wants it to be more decorative. Depending on the size and the features of your location, you may need up to two people's help with drawing the ellipse, though I will also say a little about how you can make it without drawing an ellipse.
Analemmatic sundials have a vertical gnomon (the pointer that makes a shadow) that is placed in a different location depending on the date, because the sun's position in the sky differs from month to month. They are often made with the user acting as the gnomon, and the user's shadow showing the time. The design is elliptical in shape and needs to have its dimensions and layout carefully customized for your latitude, longitude and timezone. The design does not work well for latitudes within ten degrees of the equator.
Most of my time on the project was spent writing a sundial generator script to compute the dimensions and layout for the sundial for a given latitude, longitude and timezone. But you don't have to do that. You can now just go to my Analemmatic Sundial Generator website, input your location data, and the generator will automatically produce a PDF file you can print out that has all of the dimensions you need to measure out and draw the sundial. And if you want to make a small sundial (e.g., on a piece of wood or metal, with holes drilled for the movable gnomon), you can just trace the drawing from the PDF file. The script is open source, so you can download it and modify it for your own purposes.
The theory of analemmatic sundials is nicely explained here in mathematical detail (I got most of the formulas for my generator from there). You can also see the Wikipedia article for photos that might inspire you.
In the following instructions, I will assume that like me you will make the design in chalk on a large, level paved area. Please make sure you have the legal right to draw in chalk where you are doing this. This would be a great project on a college campus if there is an area where chalk drawing is allowed (or you can get permission from the administration), or else you can do it on your own driveway or a walkway if it's level. If you do it at home, you can make it permanent by painting over it.
Many variations are possible. Chalk on concrete or asphalt is not the only way. You can draw it with a stick in soil or sand or snow, for a very impermanent one. Or you could also lay it out on grass (see the Step 4 variations), and then put flagstones--or sticks, for a temporary version while camping--where the hours are, or you could just make a small one out of wood or metal.
- measuring tape and/or yardstick (both is better)
- unstretchy string (my driveway sundial needed about 22 feet of string)
- something with a right angle (e.g., a piece of paper, a box, a carpenter's square, etc.)
- chalk (I recommend ordinary board chalk for the initial drawing, and then going over with either paint or sidewalk chalk for final lines)
- enough flat and level space for the sundial (12 feet across is good for a child-sized one; proportionately more for adults; less if you want to hold a stick in place as a gnomon)
- two pencils / screwdrivers / pieces of dowel / etc.
- computer with Internet access and PDF viewer
- printer and paper (you could also take a laptop outside without printing, but you'll have a hard time keeping it free from chalk dust)
- optional: paint
- optional: magnetic compass
Step 1: Running the sundial generator
- your zip code (if you're in the US) or latitude/longitude (this site may help)
- your timezone
- whether your location has daylight savings time (time change between winter and summer time).
Now go to my script's website analemmatic.sf.net. Start by filling out your desired actual sundial width, and select the units. The units you choose will determine the units in which all your dimensions will be calculated. If you choose millimeters, centimeters or inches, the script will give you all your dimensions in these units. (Note: If you chose inches, and your sundial is not too large, your dimensions will include fractional parts, e.g., 2 7/8". Of course, decimal is used with metric units.) If you choose feet, the script will give you all your dimensions in feet and inches (and fractional parts of inches if the sundial is not too large).
Then fill out your zip code or latitude/longitude, choose your timezone, and select what you want to do about daylight savings.
I recommend you leave the "Include (x,y) coordinates" option unchecked. The one exception is if you are unable to draw the ellipse on your surface (e.g., you're putting down flagstones on grass) and want to use an alternate method that does not involve drawing an ellipse, but measuring out hour marks with two coordinates (see the second half of Step 4). Please leave the "dimensions and instructions" option checked, unless you just want to print out a scale drawing of the final sundial with no dimensions (which might be fun if you want a paper sundial).
Click on "Submit" to generate your sundial PDF. If you are having trouble viewing it, you may need to first download a PDF viewer here and/or try a different browser. Print out the file. You will now have pages corresponding to steps 2-6 in this Instructable.
Note 1: Although I will give excruciating detail of the steps, you might just find the PDF file self-explanatory.
Note 2: The instructions will include images of the PDF file for my location. Yours will look somewhat different (especially different if you're in the southern hemisphere). Do not use my images--run the generator for your own. The exact shape ("eccentricity") of the ellipse matters crucially for this design of sundial.