Intro: Polar Star Clock
For centuries, people have been able to tell time by looking at the position of the North Star and the Big Dipper. But in most people, this skill has been lost to history. But you can use this little tool to learn how, and with a bit of practice, you should soon be able to tell time at night without a watch.
The Big Dipper rotates around Polaris in a counter-clockwise direction once every 24 hours. So if you know the month, you can get a pretty solid estimation of the time. This device, using laser-cut wood and acrylic, will let you easily tell time by holding it up to the night sky.
So lets's get started on it, but first, a bit about ancient timekeeping....
Step 1: Let's Understand How It Works...
In the Northern hemisphere, Polaris stays almost stationary, and all the other night stars rotate around it. Some of these stars rotating around it include the Big Dipper, and most notably, the 2 stars (Dubhe and Merak) that form the front lip of the Big Dipper. Polaris itself is the final star at the end of the little dipper.
Depending on the month of the year, the Big Dipper is either above or below Polaris. But no matter where Dubhe and Merak are, they will always point to Polaris. And if you imagine a 24 hour clock around Polaris, you can read the time back along that imaginary line between Dubhe/Merak and Polaris.
The tricky thing is that the time dial rotates around Polaris depending on the month. On March 6, Midnight is directly above Polaris. But 6 months later, on September 6, midnight has rotated all the way around to be directly below Polaris.
With this Polaris clock, you rotate the time dial until the current month (or closest month if it's nearing the end) is centered in the window at the bottom. Then hold it up to the night sky and centre Polaris in the middle of the clear acrylic frame behind the star motif. All you need to do now is imagine a line back to the Dubhe/Merak pair and read the time closest to it on the dial. In my ilustrations, you can see an example of what approximately 7:15 pm would look like in both November and April, and how the line between Polaris and Dubhe/Merak shows you the time.
OK, enough of that ancient timekeeping and astronomy stuff, let's build!
Step 2: Get Files and Materials.
What you will need as far as tools:
- A laser engraver, preferably with sufficient strength to cut acrylic and wood as well as do the engraving. I have been using a Trotec Speedy 400 with a 80W C02 laser.
- Fine sandpaper to clear the smoke off the wood (I used 320 grit on a sanding block)
- Glue capable of bonding wood to acrylic (I used "Gorilla" brand Super glue)
As far as materials, you need:
- Clear acrylic for the faceplate (I used 1/8" clear acrylic)
- Acrylic for the spacing ring (I used 1/8" black acrylic)
- Wood for the front and back plates. (I used 1/8" maple door skins leftover from a Settlers of Catan board I recently made...)
As far as files, you will need the following SVG files you can convert to cut on your laser. (This part will be a lot easier for you than it was for me. I had to design all the pieces, but you can just download them.)
- Front Plate
- Back Plate
- Movement plate
- Spacer ring
(I also attached them all in .PJX format for those of you lucky enough to be using a Trotec machine. Those are the "Starplate" files.)
Step 3: Cut Your Files
Be safe! Lasers (and especially Sharks with laser beams) are dangerous. Know your machine, and follow all safety guidelines for it. I'm going to go with the assumption that if you have access to and know how to use one of these, you know enough to be safe around it. If you don't, read the manual and follow it!
Here you can see the Trotec software as I setup for the spacer ring, the wood as I centered it, the wood on the second pass to darken the lettering, and the acrylic as I cut it. (always leave the backing paper on it so you can just peel off all the smoke residue from the cut).
If you can't cut the files yourself, you can find companies that will allow you to email those files in and then cut them to spec.
Step 4: Clean It All Up and Assemble It All
You'll notice that your wood pieces are probably a bit smoky. That's just surface residue, and a clean piece of 320 grit on a smooth sanding block will quickly remove it all. Do that first, then hit the inside of the rings with the 320 grit as well to smooth them down so the inner time-piece rotates smoothly.
Next, glue the spacer ring onto the back-face. Once it is dry, then place the time ring in, and CAREFULLY glue the top-face onto the spacer ring. Let it dry, but make sure you give the timepiece a wiggle every now and then to make sure that no glue has seeped out and is gluing it in place. It needs to be able to rotate inside.
The pictures show the inner time piece and spacer ring sitting on top of the wood before it was cut, and then a side profile of the entire assembly.
Step 5: Take It Out and Try It!
That's it! you are now ready to teach your friends the ways of the ancients!
Rotate the inner time-piece around until the current month shows up in the window, then take it outside and hold the center star motif over Polaris. Finally, read your time back along the imaginary line pointing to Dubhe/Merak. (Also the instructions are engraved onto the front piece.)
If you like it, please give me a vote once the Space Challenge is over. I've got my eye on a few parts on Amazon that I want to build a few things with. And I will make Instructables on them...
Step 6: What Would I Do Different?
I probably will re-make this project at some point to fix a few little issues I discovered. Here is what :
- I would make the spacer ring out of thicker material than the timepiece so that the timepiece was looser
- I would increase the depth of my engraving onto the time piece by doing a few more passes. I would then paint photo-luminescent paint over the clear timepiece and then squeegee off the excess so only the engravings were filled. Should make it much easier to read at night.