Circumzenital

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The circumzenital is an astronomical-geodetic measuring instrument of medium size, with which star passages are measured through a height circle ( almucantarat ) set at a constant zenith distance . From this, several important variables in astronomy and astrogeodesy can be determined:

The exact perpendicular direction is determined from the angle difference between the angle of elevation calculated in advance for the approximate location and the actually observed angle of elevation by means of a compensation calculation and the above parameters are derived from this.

With the classic circumzenital - which was developed in the Czech Republic - the reference to the perpendicular direction is established by reflection on a mercury horizon . The light of the mirrored star is compared with the directly incident beam by coincidence and an automatic time registration of the convergence of the two images is made. The measuring principle is thus similar to the prism astrolab , as it was patented in the 1960s for the special theodolite Wild T3 and later for the second theodolite .

The weight of the instrument is around 20 kg, which is why it needs a stable measuring pillar . The measuring accuracy is better than 0.1 ", which means that it is about 50% superior to the Ni2 astrolabe , which is much easier to transport and can be used on a tripod . Czech circumzenitals were used, among other things, to determine the length of the world between observatories and fundamental stations .

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