Photographic Zenith Tube Research Articles

Image and data processing of digital zenith telescope (DZT-1) of China

The first digital zenith telescope prototype (DZT-1) of China was successfully developed by National Astronomical Observatories, Chinese Academy of Sciences and Shandong University of Science and Technology at the end of 2011. Compared with classical astrometric telescopes, DZT-1 has features of small size, high automation, and high accuracy. It can be used to do classical astrometric observations as well as measurement of plumb line variation and deflection of the vertical. So DZT-1 plays a significant role in astronomy and geoscience. Although the measurement principle and method of DZT-1 are somewhat similar to classical photographic zenith tube, there are still many differences. The present paper introduces the principle, method, and procedure for processing DZT-1 star image and data, as well as the application software for astronomical latitude and longitude calculation using DZT-1 observations. The test observations and the observation results are also presented. According to the test observation results, the standard deviation of single observation is about 0.2″–0.3″, and 0.07″–0.08″ in term of a group observations. In conclusion, the data processing software fulfills DZT-1’s demand for data processing, guaranteeing the automation and high accuracy for DZT-1.

Development of a digital zenith telescope for advanced astrometry

Like other optical astrometric techniques, the Photographic Zenith Tube (PZT) has played a key role in the past observations of the Earth rotation, and it also has a potential to be applied to several other observations by taking advantage of automatic observations with self compensation of tilt of the tube. We here propose In-situ Lunar Orientation Measurement (ILOM) to study lunar rotational dynamics by direct observations of the lunar rotation from the lunar surface by using a small telescope like PZT with an accuracy of 1 milli-seconds of arc (1 mas) in the post-SELENE mission. Our second application is to obtain local gravity field on the Earth by combining deflection of the vertical measured by PZT and the position measured by Global Positioning System (GPS) or Global Navigation Satellite System (GNSS). The accuracy required for this purpose is not as strict as ILOM. We have already developed a Bread Board Model (BBM) of the telescope for ILOM and made some experiments in order to know the performance of the driving mechanism under a similar condition to the lunar environment showing high vacuum, large temperature change and dusty condition. We have also shown that it is possible to correct the effects of uniform temperature change upon the optical system by using a simple model with an accuracy of better than 1 mas. This model has the potential to attain the accuracy of 1 mas, based on the results of the experiments and the simulations.

Error analysis of proper motions in decination obtained for 807 Hipparcos stars from PZT observations over many decades

AbstractAfter publication of the Hipparcos catalogue (in 1997), a few new astrometric catalogues have appeared (TYCHO‐2, ARIHIP, etc.), as a good combination of the Hipparcos satellite and ground‐based data, to get more accurate coordinates and proper motions of stars than the Hipparcos catalogue ones. There are also investigations on improving the Hipparcos coordinates and proper motions by using the astrometric observations of latitude and universal time variations (via observed stars referred to Hipparcos catalogue), together with Hipparcos data, carried out during the last few years. These kind of ground‐based data were collected at the end of the last century by J. Vondrák. There are about 4.4 million optical observations made worldwide at 33 observatories and with 47 instruments during 1899.7–1992.0; our Belgrade visual zenith telescope data (for the period 1949.0‐1986.0) were included. First of all, these data were used to determine the Earth Orientation Parameters – EOP, but they are also useful for the opposite task – to check the accuracy of coordinates and proper motions of Hipparcos stars which were observed from the ground over many decades. Here, we use the latitude part of ten Photographic Zenith Tubes – PZT data (more than 0.9 million observations made at 6 observatories during the time interval 1915.8–1992.0), and combine them with the Hipparcos catalogue ones, with suitable weights, in order to check the proper motions in declination for 807 common PZT/Hipparcos stars (and to construct the PZT catalogue of μδ for 807 stars). Our standard errors in proper motions in declination of these stars are less than or equal to the Hipparcos ones for 423 stars. The mean value of standard errors of 313 stars observed over more than 20 years by PZT is 0.40 mas/yr. This is 53% of 0.75 mas/yr (the suitable value from the Hipparcos catalogue). We used the Least Squares Method – LSM with the linear model. Our results are in good agreement with the Earth Orientation Catalogue – EOC‐2 and the new Hipparcos ones. The main steps of the method and the investigations of systematic errors in determined proper motions (the proper motion differences with respect to the Hipparcos values, the EOC‐2 ones and the new Hipparcos ones, as a function of α, δ, and magnitude) are presented here. A comparison of the four catalogues by pairs shows that there is no significant relationship between the differences of their μδ values and magnitudes and color indices of the common 807 stars. All catalogues have relatively small random and systematic errors which are close to each other. However, the comparison shows that our formal errors are too small. They are underestimated by a factor of nearly 1.7 (for EOC‐2, it is 2.0) if we take the new Hipparcos (or Hipparcos) data as reference (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Corrections to the Hipparcos proper motions in declination for 807 stars

We used the data on latitude variations obtained from observations with 10 classical photographic zenith tubes (PZT) in order to improve the Hipparcos proper motions in declinations ?? for 807 stars. Part of observing programmes, carried out during the last century for the purpose of studying the Earth's rotation, were realized by using PZT instruments. These observations were performed within in the intervals (tens of years) much longer than that of the Hipparcos mission (less than 4 years). In addition, the annual number of observations for every PZT programme star is several hundreds on the average. Though the accuracy of the star coordinates in the Hipparcos Catalogue is by two orders of magnitude better than that of the star coordinates from the PZT observations, the large number of observations performed a much longer time interval makes it possible to correct the Hipparcos proper motions and to improve their accuracy with respect to the accuracy given in the Hipparcos Catalogue. Long term examinations of latitude and time variations were used to form the Earth Orientation Catalogue (EOC-2), aimed at a more accurate determination of positions and proper motions for the stars included. Our method of calculating the corrections of the proper motions in declination from the latitude variations is different from the method used in obtaining the EOC-2 Catalogue. Comparing the results we have established a good agreement between our ?? and the EOC-2 ones for the star sample used in the present paper.

The new CCD Zenith Tube

AbstractThe reconstruction of the Photographic Zenith Tube (PZT) at Ondřejov has been finished recently. The main improvement of the instrument consists in the replacement of the photographic plate with the CCD chip, and a completely new electronic control system. In addition to the astrometric use of the observations we intend to derive the variations of the local vertical and compare them with gravimetric observations of the nearby station Pecný.

Improvement of Hipparcos proper motions in declination

More than a decade elapsed after the HIPPARCOS ESA mission (ESA 1997) observations have been collected. This first astronomical satellite mission was less than 4 years long so that 1991.25 is the epoch of the HIPPARCOS Catalogue. Many other projects have checked or improved HIPPARCOS data. Also, a long series of ground - based optical observations of some stars included in HIPPARCOS Catalogue, made with Photographic Zenith Tubes (PZT) are useful for the task of improving the proper motions of these stars. The ARIHIP Catalogue (after ACT, TYCHO - 2, FK6, GC+HIP, TYC2+HIP) is a combination of the HIPPARCOS and some ground - based data, and the ARIHIP proper motions are more accurate than the HIPPARCOS ones. Here we present a new step of our procedure of calculation; between PZT data we added the HIPPARCOS position with suitable weight - the point with the coordinates (1991:25, 0 . 00 0) in our case. The method was applied to 202 stars observed at Richmond PZTs in the course of a few decades. The result is better proper motions in declination for these HIPPARCOS stars, and a good agreement with ARIHIP proper motions (we found 128 common Richmond and ARIHIP stars to check our result). Also, we present the result for other 74 Richmond stars which are not found in ARIHIP.

Photographic zenith tubes observations to improve HIPPARCOS proper motion in declination of some stars

A procedure of calculation and results of an attempt to improve proper motions in declination for some HIPPARCOS stars are presented. A long series of optical observations of these stars observed with Photographic Zenith Tubes (PZT) are used. The HIPPARCOS ESA mission (ESA 1997) was nearly 4 years long, but each of the different Earth rotation programmes (PZTs included) covers a few decades in the interval 1899.7 1992.0 (Vondr?k et al. 1998). The HIPPARCOS mission period of a few years only is not enough to determine the precise proper motions for some stars, with the standard error of proper motions of about 1 mas/year, but groundbased data covering a few decades with positional errors one or two orders higher than HIPPARCOS ones are nevertheless useful for checking or improving some HIPPARCOS proper motions (mostly of double and multiple stars). Here, the observations of two PZTs (with different longitudes and the same latitude) are used to improve some HIPPARCOS proper motions in declination; the method is explained and some results are presented. .

Kitab as One of the Five Stations of the ILS: History and Present

AbstractThe Tashkent Astronomical Observatory (Ulugh Beg Astronomical Institute of the Uzbek Academy of Sciences since 1966) was involved to the International Latitude Service (ILS) in September 1899, when the regular latitude measurements were started at Tschardjui (ϕ = +39°08′11″,λ = −63°29′). Because of the Civil War in Central Asia, the latitude observations were ended at Tschardjui in May, 1919. A new latitude station was established at Kitab (Uzbekistan) at latitude ϕ = +39°08′40″ and longitude λ= −66°53′, in November 1930. The Kitab Latitude Station was equipped with two visual zenith telescopes (1929, 1957) and the photographic zenith tube removed from the Pulkovo observatory in 1978. The Kitab station provided the ILS with more than 250000 instantaneous latitude measurements. Since the early 90s Kitab has hosted the ground-based beacons of GPS, PRARE and DORIS satellite tracking systems, providing the IERS data center with precise coordinates at sub daily frequency.

Lateral Image PZT. Description and Operating Method

AbstractWe faced the problem of designing and building a Photographic Zenith Tube with mercury basin and lateral plate-holder system providing enough accuracy to allow the determination of astronomical coordinates. This instrumentis intended to work as a prototype of a bigger and more accurate one to be designed and developed in the future (Lopez, A. et al.: 1983).

The Use of Astrometric Instruments in Vacuum Chambers

This paper discusses the effect of using a vacuum chamber with a horizontal entrance window to eliminate astronomical refraction, dispersion and irregular refraction in a telescope tube. Some engineering problems arising in connection with the entrance window are dealt with. The actual results obtained by vacuum photoelectric astrolabes and a vacuum photographic zenith tube are presented.

Tianjin photographic zenith tube observations

In this paper we analyse the observational data obtained by the Chinese-made PZT in the two periods 1979 Feb – 1980 May and 1981 Dec – 1983 March. The internal accuracy of single star is found to be m u = ±13.0 ms, m φ = ±0. “144 for the first period, and m u = ±14.6 ms, m φ = ±0.” 152 for the second. Correction of star position is found by the chain method. The systematic error caused by the sealed window of the evacuated chamber and the temperature effect of the plate scale are investigated. Monthly means of time and latitude are given.

Observations of Mars with the photographic zenith tube

Observations of Mars with a photographic zenith tube during the oppositions of 1975 and 1978 are described. A brief review of the reduction procedure is given. Analysis is made of the effects of chromatic aberration and ephemeris errors. Possible uses are suggested for the results of this analysis in further research.

Some Advantages and Disadvantages of a Photographic Zenith Tube

The theory and instrumentation of a photographic zenith tube (PZT) have been described by various authors (Torao, 1959; Markowitz, 1960; Thomas, 1964; Schuler, 1968; Takagi, 1974). Analysis of the more recent results of the PZT's of the U. S. Naval Observatory at Washington, D. C. and Richmond, Florida, permit the determination of precision and accuracy estimates which may be expected from the daily operation of a PZT. This analysis shows precisions of in latitude and in time, determined from the internal error of one sight. Accuracies estimated from the external error of a sight were found to be in latitude and in time.

Tidal Perturbations in Astronomical Observations

Twenty years of time and latitude observations made with the Herstmonceux Photographic Zenith Tube have been analysed to determine the phase and amplitude of deflexions of the local vertical at the frequency of the semi-diurnal M2tide. The results have been compared with predictions incorporating new calculations of the gravitational attraction due to the M2tides in the surrounding seas. The effects of the zonal Mmand Mftides on the time observations have also been determined and compared with existing theory. In both cases the agreement is reasonably good.

A photographic zenith tube made in China

This paper describes the various parts of the photographic zenith tube designed and made in this country and discusses the problems of working the PZT in vacuum.

Observations of the fortnightly nutation terms and the "dynamical variation of latitude" with photographic zenith tubes

Abstract : Observations made with three photographic zenith tubes show fortnightly nutation terms in good agreement with values determined from Earth tide observations. The radius of the circular dynamical variation of latitude occurring with the argument (alpha-2L) is found to be less than the rigid Earth values.

The 65 cm PZT of the U. S. Naval Observatory

AbstractThe Time Service Division of the U.S. Naval Observatory has undertaken a program to construct and install at Washington, D. C. (latitude +39°) a 65 cm photographic zenith tube (PZT) telescope to be used in studies pertaining to the rotation of the Earth. It is expected to improve the precision with which the rate of rotation of the variation of latitude can be determined by photographic techniques and, in addition, will make possible more frequent determinations of these qualities. Due to itp larger field of view, direct intercomparison with the results obtained with other instruments near latitude, +39° will be feasible. Also, it is expected to contribute to studies of the proper motions of stars near declination +39°.

The variation of latitude based on U.S. Naval Observatory photographic zenith tube observations

Following the rereduction of observations made with the Washington, D.C., and Richmond, Florida, photographic zenith tubes of the U.S. Naval Observatory the variation of the astronomical latitude of both stations with time has been investigated. The annual and Chandler variations have been analyzed and appear to be consistent with models of the Chandler motion that consider either a multiple or a single frequency. It is shown that although the appearance of the spectrum may be affected by a possible random phase change, a Chandler wobble made up of two frequencies must also show an apparent phase change in the Chandler variation of latitude. Additional evidence for the existence of a multiple-frequency Chandler wobble must wait until the mid-1980's, when another ‘phase change’ should be seen. Meanwhile, it is suggested that the method of exciting a multiple-frequency Chandler wobble be thoroughly investigated geophysically.

Star catalogs for the Washington and Richmond photographic zenith tubes.

Star catalogs for the Washington and Richmond photographic zenith tubes.

New Method for Direct Determination of UT1

ALTHOUGH Atomic Time is now available (for example as coordinated time, UTC) to a precision far in excess of that to which any astronomical time scale can be determined, astronomers, navigators and surveyors, concerned with their position on the rotating Earth, still require a knowledge of Universal Time, UT1. Universal Time is obtained by calculation from observed sidereal time, usually measured by timing the passage of stars across the meridian with a transit circle, or, more recently, with a photographic zenith tube. This measure of Universal Time, UTO, contains irregularities due to both polar motion, sometimes known as Chandler Wobble, and variations in the rate of rotation of the Earth, and its value at any instant depends upon the position of the observer on the Earth.