I'm not sure how to answer all of Chris' comments on the Kansas City star disk.
A byproduct of the stereographic projection is that the star projections are seen like you are looking at the sky from outside the celestial sphere. That is, like you are looking at a celestial globe. It doesn't bother me in the slightest, but I've been looking at stereographic star maps for many years. No one I talked to in the park seemed disturbed by the orientation. The projection used for the anaphoric disk is exactly the same as used for an astrolabe rete. It just has more stars. We considered making it in the form of a planisphere, using the azimuthal equidistant projection. This has the advantage of showing the sky as you see it and the entire horizon is shown. The disadvantages are that a planisphere is intended to be held above the head, which is hard to do in a park and the constellation asterisms are distorted enough to be noticeable. Historical significance is also not a factor with the planisphere and it is important to the overall theme of the park to encourage a historical perspective. We also considered an astrolabe clock, but it was judged to complicated for the park visitor to understand. The form we settled on is easy to understand and communicates more than enough astronomy to satisfy the park visitors. At least, the one's I talked to. The lack of astronomical knowledge of the public-at-large is appalling. North polar projections have been used for monumental astrolabe clocks, none of which have stars: only the sun (and the moon). It has also been incorporated into astrolabes and stereographic quadrants. It does improve the appreciation of the horizon, but none of the stars above the Tropic of Cancer would appear on the disk. One of the nice talking points with the projection used is to point out how circumpolar constellations are shown. We (by which I mean, I) decided to stick to tradition and show the sky only north of Capricorn. Using a larger scope would improve the amount of coverage, but at the disadvantage of introducing rather severe distortion of the constellation asterism. Full horizon astrolabes are called 'kamal' (complete) in Islamic astrolabe literature. There are many tradeoff's to consider when designing a public project of this type. Everyone involved in this project understands that some technical compromises were required to move it from the realm of machine to art. It really is pretty. Particularly at night. Best regards, Jim James E. Morrison [EMAIL PROTECTED] Astrolabe web site at http://astrolabes.org --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
