The Konkoly Observatory was established as a public institution in Hungary in 1899, when Nicholas von Konkoly Thege (1842–1916) bequethed his private observatory at Ógyalla to the state. Konkoly himself was one of the pioneers in the new science of astrophysics, and he was an expert in astronomical instruments used for photometry and spectroscopy.

In this paper I review, from a global perspective, the 1890s decade as ten years of prodigious achievements in stellar astronomy, with many huge programmes being launched and undertaken in spectral classification, radial velocities, photometry and astrometry. New astrophysical observatories were founded in America and Europe and new large telescopes designed and built, and the first international conferences were held in astronomy.

Astrophysics was still a largely qualitative science in the 1890s, but this was soon to change in the early years of the present century. I review the development of astrophysics in the 1890s, its interaction with new discoveries in physics, and comment on some of the large projects in stellar photometry, spectroscopy and astrometry and especially the influence of photography on observational astrophysics. The place of Nicholas von Konkoly in this overall endeavour is discussed and I pay tribute to his considerable influence and to the observatory he founded. A century of state-funded astronomy in Hungary has been the result.

The ongoing microlensing searches have generated more photometric measurements of pulsating stars than all previous observing projects combined. In particular, OGLE has made ∼ 340,000 B, V, and I-band measurements of ∼ 1,300 Cepheids in the Large Magellanic Clouds accessible over Internet. Microlensing searches contributed to the development of very efficient image subtraction software which works best in crowded fields. This suggests the use of a period – flux amplitude rather than period – luminosity relation for the Cepheids for distance determination, as the flux amplitude is directly measurable with the image subtraction, and it is not biased by crowding. Future projects will dramatically increase the data rate, will provide all-sky coverage and a complete census of variables, including pulsating stars, to the ever fainter limits. Time will show which approach, a small number of large teams or a large number of small teams, will be more productive.

Four large-to-medium size photometric surveys are being conducted by Warsaw astronomers: the Warsaw-LCO survey of globular clusters, OGLE, DIRECT, and ASAS. In this contribution I provide short descriptions of these projects and discuss briefly some results obtained for pulsating variables.

We review the current status and future prospects of the PLANET collaboration, an international team of astronomers performing high-precision photometric monitoring of microlensing events. Our photometric precision and sampling is characterised and the suitability of the database for variable star studies is discussed. Preliminary results on K-giant stability are presented.

A review of the MOA (Microlensing Observations in Astrophysics) project is presented. MOA is a collaboration of approximately 30 astronomers from New Zealand and Japan established with the aim of finding and detecting microlensing events towards the Magellanic Clouds and the Galactic bulge, which may be indicative of either dark matter or of planetary companions. The observing program commenced in 1995, using very wide band blue and red filters and a nine-chip mosaic CCD camera.

As a by-product of these observations a large database of CCD photometry for 1.4 million stars towards both LMC and SMC has been established. In one preliminary analysis 576 bright variable stars were confirmed, nearly half of them being Cepheids. Another analysis has identified large numbers of blue variables, and 205 eclipsing binaries are included in this sample. In addition 351 red variables (AGB stars) have been found. Light curves have been obtained for all these stars. The observations are carried out on a 61-cm f/6.25 telescope at Mt John University Observatory where a new larger CCD camera was installed in 1998 July. From this latitude (44° S) the Magellanic Clouds can be monitored throughout the year.

We report on the analysis of HST archival data obtained with the Fine Guidance Sensors concerning a magnitude limited survey of microvariability among guide stars.

ESA and NASA are studying projects having a tremendous return on variable star research. Other national space agencies are also studying or developing projects of smaller costs but with impressive returns. The projects range from global Galactic surveys like the ESA mission GAIA which will give photometric time series for about 1 billion stars, to detailed pulsation-mode studies like the CNES mission COROT which could reach a photometric precision lower than 1 ppm. The presentation will emphasize the future astrometric, asteroseismological and planet detection missions.

Two aspects of using Hipparcos data for studying multiperiodic stellar pulsations involve (1) deriving frequencies of multiperiodic pulsators from Hipparcos Epoch Photometry, and (2) using Hipparcos parallaxes together with other data, such as the frequencies, frequency ratios and multicolor photometry, to identify pulsation modes. Details are examined by looking at the δ Scuti star DK Virginis. From Hipparcos Epoch Photometry, two frequencies are derived. These frequencies are then verified by showing that they also fit all available ground-based observations of the star. In addition, Hipparcos parallax and a photometric effective temperature are used to compare the position of DK Vir in the HR diagram with evolutionary tracks. The star turns out to be at the end of core-hydrogen-burning stage of its evolution or slightly beyond, with a mass of 2.2 M⊙, or somewhat smaller. The observed frequencies indicate that the two detected modes are p3 and p2, while the relatively large photometric amplitudes imply ℓ ≲ 2.

Image subtraction is an interesting new alternative to the classical profile fitting method (DAOPHOT or DoPHOT) for finding variable stars and producing their light curves. In crowded fields this new method can lead to large improvements in the photometric accuracy. The method is based on finding the best kernel solution in order to match two images as closely as possible. This approach leads to simple mathematical equations. It is possible to find a general solution to these equations which require very reasonable computing times. It is also shown that even in the case of a spatially variable kernel an optimal solution can be found with minimum computing time. Constant flux scaling can be imposed in this case without changing the basis of the algorithm. The method is illustrated using a set of images of the central region of the globular cluster M5. Only 26 variables were found by processing this data set with DoPHOT, while 61 were found with image subtraction. A large photometric improvement was also found for the 26 variables in common. The maximum improvement achieved by using image subtraction was a factor of 20 with respect to DoPHOT. The accuracy achieved with image subtraction is comparable to what was achieved with HST in a small region around the M5 center. One consequence of this photometric improvement was the discovery of an RR Lyrae star pulsating in a nonradial mode in M5. Finally, it is concluded that image subtraction is a technique of choice when dealing with variability, and that it is important to use it when the field is crowded. It is also important to note that image subtraction may open new possibilities in the investigation of very crowded fields, even with relatively small telescope from the ground.

We describe the technique of Principal Components Analysis (PCA) as applied to the analysis of variable star data. It is shown that PCA is an efficient way of describing light curve structure.

We briefly discuss changes in the work on the General Catalogue of Variable Stars (GCVS) necessary in the era of automatic variability discoveries and large-scale surveys.

The selection of variable stars in the Tycho catalogue was re-considered. A method based on a Kolmogorov–Smirnov test was elaborated, giving 729 candidate variable stars. This number could increase to about 1000 in the future.

A variety of methods has been applied to the Tycho suspected variable stars to find reliable periods.

Very small amplitude variable stars are detected in the Geneva photometric database. Two examples of periodic variable stars with semi-amplitudes of 6.9 and 2.9 mmag are presented.

We present the results of a preliminary search for variable objects in about 100 deg2 of SDSS commissioning data surveyed twice with Δt=1.99462 days. In particular, we find that the density of RR Lyrae star candidates abruptly ends at a galactocentric radius of 50–60 kpc.

COROT is a high precision wide field photometry experiment from space, funded in the framework of the CNES “Petites Missions” program (the PI is A. Baglin). It will observe approximately 30000 objects with mV between 4.5 and 15.5 over long observational periods (up to 150 d), with a time sampling between 1 s and 16 min, a precision of the order of 10−4 per measurement. The scientific objectives are stellar seismology and the search for telluric planets. The instrument and the core program have already been presented in several places. We here focus on a description of the characteristics of the data to be obtained with COROT. The large amount of high quality data collected by COROT will constitute rich material for several research programs beyond the core program as already defined (http://www.astrsp-mrs.fr/www/corot.html). A call for proposal of additional programs will be made during Northern Spring 2000.

Future space and ground-based survey programmes will produce an impressive amount of photometric data. The GAIA space mission will map the complete sky down to V = 20m, and produce time series for about 1 billion stars. Survey instruments such as the International Liquid Mirror Telescope will observe slices of the sky down to V = 23m. In both experiments, the opportunity exists to discover a huge number of variable stars. Predictions of the expected total number of variable stars and the number of variables in specific subgroups are given.