We have an interesting meridian determination problem that might benefit from the collective experience of the sundial community.
I am working on a city park renovation project in downtown Kansas City, MO. The centerpiece is a ten foot (3 m.) diameter anaphoric "clock". An anaphoric clock has a rotating disk with stereographically projected stars and the ecliptic circle. The disk rotates under a grid showing the meridian, right horizon, tropics and local horizon. It shows the positions of the stars when it is set to local sidereal time. I say "clock" because the disk does not rotate by itself, but is set using a crank to turn the disk (the city did not want to maintain a clock movement, but we're making it so one can be added later if desired). The base has the calendar engraved on it and the margin of the star disk has a time scale. The time is aligned with the date to set the disk. As a public display, the alignment does not have to be perfect to get a good sense of the sky. The disk will be very pretty. It has holes with lenses for the stars and is lighted from below. Constellation asterisms are shown and the mythological characters associated with the constellations are engraved on the disk. It is not critical to the project that the meridian be astronomically correct, but we want it to be a close to perfect as possible. The problem is that the park is in the center of a big city, surrounded by tall buildings. We can't use the sun to determine the meridian this time of year because the park is always in shadows. The surveyors wanted to use GPS or magnetic compasses, neither of which would be reliable in this urban setting. The best I have been able to come up with is to wait for a nice, clear night and set up a telescope (or equivalent) over the center of the clock. Then wait for the meridian passage of a star of known right ascension that is visible. I can calculate the precessed right ascensions of some stars and the time of meridian passage. The idea is to center the star in a telescope with an accurate drive and then just stop the drive at the right instant and use the scope's mount to locate the vertical plane. The theory is sound, but there are a number of practical problems related to telescope mounts to be resolved. We have the support of the local astronomy club for equipment and expertise in using it. We are restricted to a zenith distance at culmination of about 40 degrees, which gives us access to Betelgeuse, Bellatrix and Aldebaren this time of year at a reasonable time of night. Does anyone have suggestions on the best way to approach finding the meridian when you are in a big hole? Happy New Year, Jim James E. Morrison [EMAIL PROTECTED] Astrolabe web site at astrolabes.org --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
