Photographic zenith telescope

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The photographic zenith telescope , PZT for short , is the most precise type of instrument for astronomical measurements of direction and time. The instrument, which can only be used stationary for institutes of the Pole and Zeitdienst, is a specialization of the visual zenith telescope .

Like this, it is a high-precision, stationary measuring instrument of astrometry for the most precise possible determination of star locations and a fundamental system of celestial coordinates , astronomical latitude and sidereal time - i.e. the exact vertical direction of the observatory and its temporal changes, which in the global network and with methods of satellite geodesy for Monitoring of the Earth's rotation and pole movement contributes.

The PZT is used to take photographic recordings of star fields close to the zenith - as a point of penetration of the vertical through the celestial sphere - and to precisely measure star locations.

Between the individual recordings, which can achieve accuracies of up to a few 0.01 ″ after adjustment, a rotation of 180 ° (possibly also 4 × 90 °) is usually carried out. This makes it possible to determine the exact position of the axis under the photographed stars. The image coordinates measured in the images are converted into the inertial system of the star coordinates by special astrometric transformations . The center of the image then corresponds to the sky coordinates of the zenith .

The abbreviation PZT is used much more frequently in astronomy and geodesy than the long term. It also sets the instruments apart from the zenith cameras (abbreviated to ZK or ZC ), which are not elongated, but much more compact and now work largely with newer sensors such as CCDs instead of photography .

Examples

The Central Institute for Earth Physics and the Ondřejov Observatory used the PZT 2 from 1980 to 1990 , a PZT developed and built by VEB Carl Zeiss Jena with an opening of 250 mm, to determine the width . Seasonal fluctuations in the earth's movement were also determined.

The United States Naval Observatory uses a PZT to determine Universal Time .

literature

  • Karl Ramsayer 1969: Geodetic Astronomy . Handbook of Surveying Volume IIa, JB Metzler-Verlag Stuttgart, 902 p. (p. 243-247 et al.)
  • G Damljanovic, G Gerstbach, M de Biasi, N Pejovic (2003): CCD Technique for Longitude / Latitude Astronomy. Proceedings XIII Nat Conference p. 229-235, Astr. Ob. Belgrade No.75, 2003
  • Manfred Meinig: Changes in width of the Potsdam station . In: Astronomical News: A Journal on all Fields of Astronomy . Volume 312 Issue 6, 1991, WILEY-VCH Verlag, pp. 405-411