We analize the light curve of comet P/Halley resulting from 187 observations made by amateurs. We try to derive some constraints on the physical properties of the comet through the application of the semi-empirical photometric model (SEPM) developped by R.L. Newburn.

The m1 (Fig. 2) and V(1,0) light curves show a clear transition phase in the pre-perihelion apparition, between ~ 1.9 and ~ 1.2 A.U. which supports the division into 3 parts made by Hasegawa. It is remarkable to find that the light curve obtained by amateurs is so close to those obtained by experienced observers.

We derive an effective equivalent radius of β = 4.9 ± 0.8 (1σ) km, and a geometrical albedo of pυ = 0.06 ± 0.02 (1σ) using the method suggested by Delsemme and Rud.

The ways in which amateurs may increase their chances of discovering comets were described. Amateurs discover a considerable proportion of comets, but their contribution is greater among long-period comets. The relative proportions of short-period comets is revealing: 1 in 2 for professional astronomers, 1 in 8 for amateurs. Professional discoveries are largely a by-product of searches for asteroids: the comets have low inclinations (i < 30°) and are faint (m1 > 14). Amateurs are most successful in areas close (<60°) to the Sun. Typical apertures are 150-mm, and most comets are brighter than magnitude 10.

Past results show that there is a strong correlation between number of observers and number of discoveries. Several amateurs have discovered comets at great elongations with larger telescopes (≥ 400 mm). The comets tend to be fainter (10 < m1 < 12). Several comets have been discovered with simple equipment (200- or 300-mm telephoto lenses) down to magnitude 13.

Calculations of the distribution of discoverable comets show that an average of 14 comets (9 < m1 < 14) are missed per year.

Most periodic comets are recovered by professional astronomers at faint magnitudes (18–21). Only Tsutomu Seki, using a 60-cm telescope has been an exception to this rule. Amateurs having access to large telescopes (such as the T 60 at Pic du Midi) now stand a chance of success. For example, using the T 60, the author photographed P/Halley at mag. 19–20 on forming-gas hypered Kodak TP2415 in a 1-hour exposure. Experiments by C. Buil suggest that the same telescope can reach magnitudes 21–22 with a CCD array cooled to – 50° C and a 30-minute integration time.

Observations made since the comet’s discovery (1927) were analyzed and reduced to remove observational bias. Comparison was made with possible mechanical effects on the nucleus (tidal forces, impacts). The observations appear to best fit an internal mechanism (exothermic chemical reactions) as proposed by Whipple.

Details of H2O and dust production in P/Halley are mainly derived from amateur observations of cometary tails, leading to a gas/dust mass-ratio. The rotational period (2.21 day) is also found from amateur observations. Velocity and acceleration of the plasma and velocity and direction of the solar wind are also derived, together with size and indications of the mass-distribution function for dust particles.

These techniques have been applied to other comets, giving interesting results on differences between various comets. There is a lot of information available in cometary photographs. The coordination and archival storage of such information is urgently required.

The total solar eclipse of 1984 November 22/23 was observed from a French naval vessel off Noumea (New Caledonia) in the Coral Sea. The observations were made by a team from the S.A.F., led by Serge Koutchmy and Christian Nitschelm of the Institut d’Astrophysique de Paris. The duration of the eclipse was considerably longer off New Caledonia (1 m 39 s) than in Papua-New-Guinea (55 s). However, the observational site – on board a ship well out to sea – greatly restricted the use of long-focal-length instruments that are normally employed. The equipment used to photograph this eclipse therefore was chosen with motion (pitching, rolling, etc.) of the support in mind. Short focal lengths were preferred, although one refractor with a focal length of 1.5 m was used as a trial.

The modification of properties of granules around magnetic flux tubes has been studied for the first time from photographs (at λ = 4803Å and 5770Å) taken with the 50-cm refractor at Pic du Midi. Statistically, these granules are more numerous, smaller, and more elongated than other granules. During their first two minutes of life they show very pronounced radial orientation to the magnetic flux tube.

Angular measurements on the same granules have a precision of ± 10°, which is sufficient as theoretical studies show that they rotate by 360° in the course of their life. Initial results appeared to show that only explosive granules had intrinsic rotation, but further examination showed that it is a general trend. It seems that the granules do rotate significantly, but that there is a more important “push-pull” effect, in agreement with A. Title’s theory drawn from SOUP images.

The method of placing the solar limb tangential to the slit, which is then widened, has been employed. The following phenomena have been observed: fast radial motion of low loops; extension of the main loop into the corona; ejection of material from the top of the loop; rotation of the structure as it relaxes.

The results of the IOTA expedition to Gabon to observe the rare total-annular eclipse of 1987 March 29 were described. Multiple stations were used to determine data from Baily’s Beads about the contact times. The techniques used and their application to future eclipses were evaluated. An additional aim was to develop a database to resolve corrections to the solar radius at specific epochs in order to determine the amplitude of time-dependent oscillations of the Sun’s surface.

Historically meteor astronomy is one area where amateurs have always been able to make significant contributions. In fact, in the 19th century, it was amateur naked eye and telescopic observations which laid down much of the foundations of meteor astronomy. References to this work can be found in any textbook on meteors. The 19th century observers concentrated on counting meteors, estimating magnitudes and plotting the meteor paths on star maps. Their main interest was to determine hourly rates and shower radiants. An important milestone was Denning’s radiant catalogue (Denning 1882), which included 4367 shower radiants. Although it is now believed that many of these radiants are spurious, the catalogue is still a useful reference. Unfortunately Denning and other 19th century observers often combined sporadic meteors observed on different nights into a minor stream radiant. This habit of “radiant hunting” is even today quite popular among some amateur observers. However, in all fairness it should be emphasized that most of the 20th century amateur meteor observers applied very strict criteria to their radiant determinations. Names such as J.M. Prentice in Great Britain, R.A. McIntosh in New Zealand and R. Rigollet in France may be mentioned.

“Sonate” (Sondages acoustiques pour l’évaluation de la qualité d’images des téléscopes) – Acoustic sounding to estimate the quality of telescope images – is a prime example of professional/amateur collaboration as it involved 3 professionals and 22 amateurs, who, in order to collect the maximum amount of data, relayed one another in 10-day shifts over a period of 4 months in 1984, using the 1-m telescope at the Pic du Midi. A preliminary campaign with the 2-m telescope in 1982 had shown that the profile of sound waves reflected from the layers above a site could be correlated with the quality of telescopic images at the same site.

The Solar Section of the Societé Astronomique de France has organized various programmes designed to enable amateurs to carry out high-quality and scientifically useful observations. Two particular programmed will be described.

Professional solar astronomy concentrates on the study of the atmosphere and interior of the Sun. Little attention is given to “classical” programmes, mainly statistical investigations of solar activity. Although the main properties of phenomena associated with the solar cycle seem to be understood there are still enough details to be explained, making it worthwhile monitoring different indicators of solar activity, even if no immediate results are to be expected. Such routine observations are ideal work of amateur astronomers.

Members of West German local astronomical societies founded the journal Sonne in 1977 to combine their efforts on solar observations. The first issue was presented at a conference on amateur solar observation held in Berlin in April 1977. Sonne is compiled by an editorial staff of 23 amateurs from all over West Germany, and is distributed among nearly 500 readers in 20 countries. With the increasing number of foreign readers, the main articles in Sonne are provided with English abstracts.

Largely forgotten today is the role that amateur astronomy played in the early days of space exploration. For example, 1987 is not only the 30th anniversary of the first artificial satellite but also of history’s most successful global organization of amateur astronomers: Moonwatch.

As a worldwide network of volunteer visual observers, Moonwatch was a vital adjunct to Western satellite tracking efforts. In nearly two decades of operation, more than 500 individuals made some 400,000 observations of approximately 6000 objects. Although now only a footnote to space history, Moonwatch suggests that some comparable organization of dedicated and talented amateurs might contribute to the International Space Year of 1992.

Variable stars are a field where the contribution of amateur astronomers is of great importance. This contribution can be separated in to complementary parts:

1. 1) collaboration with professional institutes that well-equipped amateurs can easily undertake in the field of photoelectric observation;

2. 2) visual observation of variable stars, which in many cases can be a preliminary approach to photoelectric photometry.

The observation of variable stars is one of the most important and the most fruitful areas of stellar astronomy. The contribution of large numbers of visual observations is a determining factor in drawing up light-curves, the latter being the key to the interpretation of the process of variability within these stars.

It is not easy for a professional astronomer to obtain access to modern telescopes, especially to those of large aperture, and it may even be difficult, given the large number of projects put forward. In any case, these large instruments are often unsuitable for the observation of variable stars. Amateurs, on the other hand, have instruments that have a lower degree of precision, but their greater number and the good organization that exists for the reduction of data obtained, represent trump cards in preparing light-curves.

Let us divide variable stars into two main groups: the first “classical” group, includes objects known for a long time, such as Cepheids, RR-Lyrae stars, Miras, cataclysmic variables, eclipsing binaries, etc. The second group includes micropulsating variables of δ Scuti and β Cephei types, magnetic variables, rotating variables of BY Draconis type, etc.

Historically, the contribution of amateurs in investigating the first group was very significant, and it continues to increase. On the other hand, involvement in studying the second group of stars was practically equal to zero some years ago, but today one can see the beginnings of an expansion of amateur work on this second group of variables – among brighter objects, of course. One reason is the beginning of cooperation between amateurs and professional astronomers having powerful instruments.

The role of amateur astronomers in the search of extragalactic supernovae is emerging. Visual discoveries by John Bennett in 1968 and Gus Johnson in 1979 were isolated and surprising encounters, but are indicative of the possibilities. Between 1980 and the present, these possibilities have been well-tested by the Rev. Robert O. Evans, who has discovered 15 SN’s and shares credit for a 16th. Rev. Evans’ record was achieved through an organized approach to observation and assisted by the development of a unique observing regimen. Detection of SN is a formidable challenge, but the obvious conclusion is that amateurs may expect to attain more than marginal success. We approach this subject from the standpoint of visual observation, but are obliged to acknowledge the contemporaneous and successful application of photography as a search tool.