Various types of occultations and eclipses offer individuals with access to small telescopes the opportunity to contribute significantly to modern solar system research. In fact, often it is only through the cooperation of several such observers that the desired scientific objectives can be realized. This review discusses three classes of occultations which are of high current interest and which are particularly suitable for investigation with small telescopes.

Using a number of different conventional observing methods of astronomy like spectrophotometry, polarimetry, IR-radiometry and UBV-photometry, physical properties of asteroids can be derived, such as diameters, spectral reflectivity and albedo. Based on observable parameters a classification in terms of taxonomic types can be made and the mineralogy of the surface can be determined and compared with meteoritic analogues. UBV-photometry at different phase angles can reveal something about surface properties and diameters, whereas from accurate photometry during different phases of the rotational cycles we are able to derive rotation periods, geometric irregularities of the asteroid-body and topographic features on the surface. If observations of lightcurves are obtained during several oppositions at different ecliptic positions, the orientation of the spin axis in space and sometimes the sense of rotation can be derived. Observations of asteroids are especially well suited to small and medium-sized telescopes, as most of the programmes need long telescope runs. In addition there is a definite need for a large number of observations of asteroids in the magnitude range 12–15 mag.

Because comets are so difficult to observe, it is essential to coordinate observations from a variety of telescopes in order to fully understand their behavior. The apparition of Comet Halley represents a unique opportunity for coordinated programs because this is the only predictable comet which is routinely bright enough for the many observational programs desired. The International Halley Watch is playing an advocacy and coordinating role in the observations of Halley. Coordinated photographic observations will provide a record of the development of jets in the coma and of the motion of features in the tail. Coordinated photometry will provide both the heliocentric variation in vaporization and also the details of the outbursts thought to occur in most comets. Coordination with larger optical telescopes and with radio and infrared telescopes will allow a more complete understanding of the physical and chemical processes occurring in comets. Examples, of course, must still be drawn from observations of previous comets but they illustrate the results expected from Halley.

Current research programmes using the smaller telescopes at Kitt Peak include spectroscopy, photometry, and imaging of clusters, variable stars, nebulae, and extragalactic objects. Their scientific productivity is competitive with the 4m and 2.1m telescopes. Subscription rates indicate that when advanced instrumentation is made available on a small telescope, the demand will increase significantly.

A new program of accurate photoelectric photometry for the brightest stars is getting underway, using the excellent small telescopes and talents of amateur astronomers.

Surface photometry of relatively bright galaxies is now becoming almost an exclusive province of small telescopes equipped with CCDs. I give a brief review of the scientific possibilities and problems of interest in this field. Small telescopes become tools of observational cosmology: they can provide large amounts of data necessary for the further understanding of fundamental properties of galaxies, clues to their formation, and their interactions with environment.

At the General Assembly of the IAU at New Delhi van Altena reported on the new General Catalogue of Trigonometric Stellar Parallaxes (GCTSP) which was completed recently at the Yale Observatory. Time seems to be ripe now for the compilation of a Third Catalogue of Nearby Stars which will include all objects known to be nearer than 25 parsecs. This catalogue will contain positions, proper motions, radial velocities, spectral types, broad-band photometry, and parallaxes - quantities won by observations.

Study of the solar interior through analysis of solar oscillations, a field now referred to as helioseismology, has generated interest in the development of asteroseismology, the study of the interior of pulsating stars through the analysis of their oscillations. Some progress has been made in the study of the Rapidly Oscillating Ap stars, cool magnetic Ap stars which pulsate in high overtone, low degree non-radial p-modes with periods between 4 and 15 minutes. Since all of these stars found so far are bright (V<10), their light variations can be studied with small telescopes; most of the work done has been with a 0.5-m telescope. Their light variations are extremely complex, however, which means that they must be intensively observed, something which can only be done with small telescopes. Due to aliasing problems, multisite observing programs of the Rapidly Oscillating Ap stars are often necessary in order to decipher their frequency patterns. A collaborative observing program is suggested.

The functioning of a project for systematic observations of variable stars on a long time scale is described.

Polarization of radiation in the UBVRI spectral bands of the stars in the vicinity of four Bok Globules/dark clouds is observed with 1.5 and 1m telescopes. Moderate to high degree of polarization and alignment of polarization vectors indicate the possibility of frozen magnetic fields. Other possibilities for retarding the cloud collapse have also been pointed out.

Using our intermediate bandwidth photometric scanner, we have obtained light curve data at a range of spectral intervals for a number of close eclipsing binary systems. This paper reports briefly on the instrumentation system, the data obtained for two of the variables AE Phe and ε CrA, and a preliminary modelling of the light curves.

Initial observations using uvby filters with a CCD detector were completed in June of 1985, using the Cerro Tololo 4m PFCCD system. It has been possible to derive all Strömgren indices (b-y, m1 and c1) for V<18 from frames with acceptable integration times. For fields in the open cluster IC 4651, averages of 2 to 3 frames with exposure times of 15, 20, 40, and 500 seconds for the y, b, v, and u filters, yielded high precision magnitudes and indices for V<15. Exposure times up to 5 times longer were required for the v and u filters in order to derive c1 indices of sufficient precision for stars with V between 15 and 16. One result of our survey is the apparent absence of main sequence stars below V = 15.

The usefulness of photography in long term studies of variable stars is demonstrated by recent results on pulsation periods. Photography has been in use long enough for evolutionary changes to be detected, at least during stages that are relatively rapid, such as after core He exhaustion.

The New South Wales Branch of the British Astronomical Association is currently making use of the Sydney Observatory astrograph for cometary astrometry. Astrometric plates (16 × 16 cm) of P/Halley are being taken at a plate scale of 116 arcsec/mm with a field of 5 × 5 degrees. Plate measuring is accomplished by means of a mechanical single screw Hilger measuring machine. Plate reduction utilises the program supplied by the International Halley Watch organisation. Measurement and reduction is facilitated by the machine readable catalogue and plotting routines supplied by the United States Naval Observatory. Currently the BAA observing team is working towards achieving a 24 hr turnaround for plate reductions. This will enable useful contributions to be made during the critical pre-encounter periods.

The relation existing between the radius and the period for the pulsating stars of a given class constitutes a powerful test for the theory of stellar evolution and for the identification of the pulsation modes. In recent years, several authors have determined the mean radius of a lot of pulsating stars of various classes by applying the Baade-Wesselink method. Fig. 1 presents the resulting general logP - logR diagram grouping these determinations. The sources for the radii are given by Burki and Meylan (1986). The variable stars in known binaries have been excluded since the presence of a companion biases the radius calculation (Burki, 1984). The determinations marked by arrows are based on the radial velocities by CORAVEL (1m telescope at the Haute-Provence Observatory, France) or/and on the photometry in the Geneva system (40cm and 70cm telescopes at La Silla Observatory, Chile).

Recent progress on maximum-entropy imaging of stellar surface brightness distributions using VRI photometry and Doppler-broadened absorption line profiles is reported. VRI photometry generally provides tighter constraints on starspot configurations than does Doppler imaging (which requires the use of large telescopes). Observers carrying out long-term photometric monitoring programmes on spotted stars are urged to work in the VRI system, as well as the UBV.

We are conducting a search for dust lanes, incipient stellar disks and bars, and other deviations from elliptical symmetry in a sample ∼ 250 early-type galaxies. Division by a model galaxy image is a very powerful enhancement technique for this type of work.

We report the preliminary results of a CCD surface photometry survey of a large fraction of all known Galactic globular clusters. About 1/5 of all surveyed clusters show a characteristic post-core-collapse (PCC) morphology. The PCC clusters are on average closer to the Galactic center than the King-model-like clusters.

We have been monitoring the CaII H and K emission in late-type giant stars using the Mt Wilson 60-inch telescope. It is a continuation of work that Olin Wilson began almost 20 years ago. As a result not only have starspot cycles been detected (equivalent to the solar sunspot cycle), but rotation periods have now been measured.

We use a scanning CCD for acquisition and astrometry of new and recovered comets, asteroids and other objects. The CCD is an RCA SID 53612 thinned, buried channel array of 512 × 320 30-micron square pixels that are back-illuminated and refrigerated to −60 C in a vacuum housing. The readout noise is ± 200 electron-hole pairs (ehp) per pixel per readout, the thermal dark current is 50 ehp/pixel/sec, and the scale of our 12-bit analog-to-digital converter is 25 ehp/AD unit. The Newtonian focus of a 91-cm telescope has been modified from f/5 to f/3.85 with a relay lens to give a platescale of 1.73 arcsecs per pixel, a scale chosen for efficient coverage of sky. The CCD is operated in the scanning mode with the telescope drive off, and the rate of transfer of signal charges is tuned to correspond to the rate at which the star images drift across the focal plane. The exposure time (the time the images take to transit the “512” dimension of the CCD) is 60 seconds at the celestial equator, giving a “six sigma” limiting (visual) magnitude of 19.5. A typical scan covers 30 minutes of time in right ascension by 0.156 deg in declination and is stored as a digital array of 14848 × 320 CCD pixels. A set of three 30-minute scans near the opposition point along the ecliptic nets about 5 new main-belt asteroids. Potential moving objects are revealed by determining the positions of all the stellar images in each scan and comparing the results of the three scans. Several potential reference (SAO) stars are in one scan. The reduction from pixel coordinates to apparent topo-centric equatorial coordinates of date involves only three free parameters, making our astrometric reductions simpler than the classical affine transformation of plate coordinates. There is no rotational transformation and the scale in right ascension is defined by the clock. The declination scale is determined from the reference stars. The zero points of R.A. and Dec. are given by the average differences between the pixel coordinates and catalog positions of the reference stars.