Polygons vs. Circles
In principle, I’m pleased with my circular planispheres as teaching tools, but they do have some practical flaws...mainly with the covers. The covers are a bother to cut out, and I don't have a good way of fastening the two sides of the cover together. If I could figure out how to cut out the pieces with a Cricut Machine, that would save a lot of cutting work, but it would require that you own a Cricut. Gluing the two covers together along the outer edge is easy enough, but sometimes the disk doesn't rest easily in a centered position inside the cover when you do this, and it tends to bind in the grooves when you try to turn it.
As an alternative design, I wondered if it would be possible to make a polygonal version of the planisphere. It wouldn't turn smoothly like a circular version would, but in many other respects, I thought it might make a good ‘elementary’ or ‘starter’ version, especially for younger kids when they are first exposed to the concept of ‘world map of stars’, and how to make one that you can turn to show which stars are up at any given time.
I present here my first draft of such a planisphere. It is not intended as a precision measurement device, but merely a simple introductory planisphere, suitable for teaching younger children how the constellations move. While I have successfully used the circular versions myself in real classrooms, this version is new and I have never actually tried it out with children. If you do, I’d love to hear how it goes. (Although, as with planispheres and ‘celestial spheres’ in general, I think this unifying subject is best taught after a course of familiarizing the students with the individual constellations visible in the night sky.)
The ‘disks’ are all dodecagons, with one month per side, and they are all identical regardless of latitude. (Come to think of it, maybe I should make the universal disk a separate download, and then you could download the cover for your latitude separately.) The covers contain all straight edges (except for the curve representing the horizon). There are fewer windows to cut out, and the windows contain all straight edges as well. If you want, you can even cut straight across the outer rim to get the scissors into the windows, because you can tape the outer rims back together again with tape anyway. Having straight edges, it is also easier to wrap small pieces of tape around the outer rims to fasten the two side of the cover together.
Assembling the Planispheres
To assemble the planisphere, start by printing the design onto cardstock. I have generated the PDF files so that you should be able to use double-sided printing and have your printer produce a double-sided celestial disk, with constellations and months lined up on both sides. However, I find that double-sided printing tends to be a bit quirky, and you may need to fiddle with the settings of your printer to get it to come out right.
To cut out the ‘disk’, simply cut out around the outline. Assuming your printer handles double-sided printing reasonably well, this should produce a dodecagon with the northern hemisphere of stars on one side, and the southern hemisphere of stars on the other, with the edges matching on both sides. To cut out the covers, start but cutting out the dodecagon around the outline, then cut across the middle along the horizon line, then cut out the windows by removing all pieces marked with an ‘X’. You should get three pieces that look like this:
The rest is simply a matter of taping the two sides together by passing small pieces of tape through the windows, and wrapping them around the outside rim of the cover.
There are no comments yet. Be the first to contribute.