This paper is part of a more extensive study of the large voids in spatial volumes both wide and deep. Three samples of optical tracers with spectroscopically measured redshifts in a volume with b≥30° and z≤0.14 have been extracted from the catalogue of Lebedev and Lebedeva (1986) and the NASA/IPAC Extragalactic Database (NED):

1. (1) a homogeneous sample of 277 rich Abell clusters

2. (2) an inhomogeneous sample of 969 objects: rich and poor Abell clusters, Zwicky clusters, other clusters, and groups

3. (3) a sample of 18 623 NED galaxies.

Since the first applications of wide-field photography in astronomy nearly 2 million plates and films have been obtained and stored in archives all over the world. The Wide-Field Plate Database (WFPDB) provides astronomers with detailed information about the wide-field photographic observations. Its preparation started in 1991 as one of the main projects initiated by the Working Group on Wide Field Imaging at the IAU Commission 9.

An updated data collection for UV Cet type stars and their registered flare events in stellar aggregates and in the solar neighbourhood during more than 9580 hours observing time is described. The Flare Stars Database (FSDB) presently includes 3127 entries for 1622 stars.

The current status of a database containing information on wide-field observations stored in plate archives all over the world is presented. The database will permit on-line access to information on nearly 2 · 106 wide-field (⪆ 1 degree) plates and films, obtained over more than a century with about 200 telescopes and cameras.

The present status of the work on the creation of a Wide-Field Plate Database is reported. It is planned to collect the available information for about 1.5 million plates from 187 wide-field instruments in 71 institutes/observatories. The source data are from 213 plate catalogues, 65 of them in computer-readable form. The structure and content of the Wide-Field Plate Database, now including 51 observation catalogues with more than 300,000 plates, is presented.

The 2m Ritchey-Chrétien-Coudé (RCC) telescope of the National Astronomical Observatory, situated in the Rozhen massif of the Rhodope Mountains, started operating in 1980 (for a detailed description of the telescope see Gutcke [1979]). Since then, 2000 direct photographs have been obtained, most of them covering a 1° × 1° area on the sky with resolution 12.9 sec/mm.

The results of the intensive observations of the Pleiades flare stars for more than 20 years (≈ 3000 h effective observational time) were compiled and published by G.Haro and collaborators in a catalogue (Haro et al.,1982) including the flare stars discovered in the Pleiades region up to 1981. The catalogue contains the data far 519 flare stars.

In the frame of the international programme for the study of flare stars in stellar aggregates the Department of Astronomy and the National Astronomical Observatory have carried out patrol observations in the Pleiades since 1979. Parallel to the observations, work on the creation of machine-readable versions of the published flare stars catalogues has begun. As a firatstep, a machine—readable version of the Tonantzintla catalogue (TC of the Pleiades flare stars has been prepared (Tsvetkov et al., 1987).