project a dodecahedron onto the celestial sphere, then present each of the 12 faces as star chart images for a monthly calendar. the images have no correlation with what is visible in the night sky during that month. (people in urban areas can't see much in the night sky anyway.)
both regular dodecahedron and rhombic dodecahedron would work. unspecified: map projection of each spherical polygonal face onto flat paper. regular dodecahedron induces less distortion, but maybe a projected rhombus fits more nicely on a rectangular calendar page. (but why not pentagonal calendar pages?)
also possible: cube with each face cut in half (pyritohedron) can yield nice rectangular regions. tetrahedron with each face cut into 3 can yield kites. (other shapes possible depending on how you cut.)
optimize the orientation of the dodecahedron so that every month has a good collection of labeled interesting objects. also try to avoid cutting constellations and any other large objects (can't think of any others) awkwardly. for the regular dodecahedron, a face centered on each of the celestial poles is also desirable.
annotate edges with the name of the month whose map lies beyond the edge. overlay grid of celestial coordinates (right ascension, declination).
would it be better if the views overlapped? spherical caps yield circular segments of the sky. what is the minimum size spherical cap that covers a pentagonal face of a regular dodecahedron (this should be easy)? how thick should the overlaps be? maybe variable to avoid cutting constellations awkwardly.
alternative to a star chart: cosmic microwave background.
also possible: various other spherical astronomical bodies (including earth) whose surfaces we've fully mapped. but these seem less interesting, not looking out at infinity but looking in at something finite.
for a weekly or daily calendar, find equal(ish)-area compact(ish) subdivisions of a sphere into the appropriate number of pieces. Goldberg polyhedra are pretty. there exist Goldberg polyhedra of 42 and 362 faces.
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