Is the Prague clock of the same design as the one in Bern? See e.g. http://starswebworx.lc-stars.com/swiss_photo/Bern.htm (scroll down a bit).
-- Jan On Mon, Feb 28, 2011 at 09:15, James E. Morrison <[email protected]> wrote: > Perhaps some background would be useful to those on the list who are not > familiar with astrolabes and astrolabe clocks. > > The Prague clock is based on an astrolabe with the projection origin at the > north celestial pole. This orientation causes the horizon arc to arc in the > reverse direction from a normal astrolabe, but it gives a more intuitive > representation of the Sun's position. > > The clock has three moving parts. A hand with a Sun figure rotates once in > a mean solar day and the Sun's longitude is indicated by the position of the > Sun figure on the ecliptic (which is divided by the zodiac). The astrolabe > rete, which has only the projection of the ecliptic on the clock, rotates > once in a sidereal day. The difference in the rate of the two components > keeps the Sun figure on the (approximately) correct position on the > ecliptic. The third hand shows the position and phase of the Moon. > > The Prague clock, and all other devices based on the astrolabe, indicates > apparent time with the Sun hand. The only adjustment needed for it to > indicate approximate civil time would be to simply move the Sun hand to a > time. No changes in gearing are needed. But the Sun's position in the > ecliptic (zodiac) would no longer be correct and any events (sunrise/set, > culmination, etc.) would no longer be valid. That is, the Sun figure no > longer represents the real Sun, > > It could be made to show apparent time again by simply moving the Sun hand. > > Best regards, > > Jim > James E. Morrison > [email protected] > Astrolabe web site at http://astrolabes.org > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
