Photographic Zenith Tube Zeiss (PZT) has been regularly used at Ondřejov Astronomical Observatory to determine latitude variations and clock corrections within the frame of Earth rotations service
since 1973. About 45 thousand star transits near the zenith of the observatory were observed and used to improve positions and proper motions of the stars three times, during the history of the observations. To derive the first two catalogues, PZT78 and PZT83 (based on the observations in 1973-1978 and 1973-1983 respectively), PZT observations were combined with star positions in AGK2 and AGK3 catalogues in order to obtain proper motions with higher precision. The most recent catalogue, PZT86, is based solely on PZT observations in the period 1973-1986. The algorithms used to derive all these catalogues as well as their precision and accuracy are discussed in the paper, and their comparison with AGK2/AGK3 given.
New information is provided on the distribution of 19 species of lichens belonging to the genus Caloplaca (Teloschistales) in the Czech Republic. Six species are new to this country: C. epithallina, C. erodens, C. inconnexa, C. phlogina, C. polycarpa and C. thuringiaca. The species C. albolutescens, C. cerinella, C. chlorina, C. chrysodeta, C. dichroa, C. flavocitrina, C. herbidella and C. marmorata are reported from the Czech Republic, but little is known about their distribution in this country. Caloplaca biatorina, C. obliterans, C. rubelliana, and C. xantholyta are rediscovered after more than 50 years. The presence of Caloplaca crenulatella, recently reported as new to this country, is confirmed and is actually one of the most common species of this genus. Ecological and chorological data are given for each species, and taxonomic and nomenclatural notes for C. albolutescens and C. chlorina are amended.
Nineteen isolated rocky outcrops of different sizes, tops of which were covered with natural grassland vegetation, were studied in the forested submontane belt (630–1020 m a.s.l.) of the Šumava Mts in the southern part of the Czech Republic, Central Europe. The species of vascular plants present in the treeless sites at each locality were identified. Those species with an Ellenberg indicator value for light equal 6 or higher were considered to be heliophilous. The distance to the nearest secondary treeless area was measured. There were 43 heliophilous species (23%) recorded among the 184 species identified. The number of species and the number of heliophilous species varied independently of the altitude and extent of the treeless area on the rocky outcrops, but were significantly correlated only with the distance to man-made treeless areas. The highest number of heliophilous species was recorded within approximately 400 m from the nearest man-made treeless area. Although the relict occurrence of some of the heliophilous species on the rocky outcrops cannot be completely excluded, obviously most of the species colonized these localities from nearby secondary treeless areas since their creation in the Middle Ages.
In this review paper we study the atmospheric and oceanic effects in nutation. It is a continuation and summary of our previous studies that we made during the last five years or so. We use slightly modified methods and apply them to the most recent data (both atmospheric/oceanic excitation functions and combined solution of celestial pole offsets by International
VLBI Service for Geodesy and Astrometry - IVS). We find th at the atmospheric and oceanic excitations provide significant changes in nutation, mostly with annual and semi-annual periods. The numerical integration of Brzeziński’s broadband Liouville equations yield Free Core Nutation (FCN) that is consistent with VLBI-based observed values. The analysis of VLBI observations shows small quasi-periodic fluctuations of the period and qua
lity factor of retrograde FCN, ranging between 429.8 to 430.5 days and 17000 to 22000, respectively. To this end, we use resonant effects in several dominant forced nutation terms to calculate the period and quality factor of FCN in running 6-year intervals. Numerically integrated geophysical excitations are removed fro the observed celestial pole offsets, and the remaining part is used again to derive the period and quality factor of FCN in running intervals. Our conclusion is that the observed quasi-periodic variations of both parameters are not caused by these geophysical excitations, but another source should be searched for.