The third annual GEOS symposium was held in Marly on 21–23 April 1978, gathering 43 participants, including 19 Italian observers. Because of the strong Italian presence, simultaneous translation was provided, described as made possible “thanks to the INEP equipment and especially to the skill of C. Romoli, E. Poretti and M. Penna.” The meeting focused on presenting results from studies conducted in previous years.
Several observers reported on their work. J.F. Le Borgne presented an analysis of V 1264 Cyg, comparing two competing periods and showing that the Russian period of 2.17 d contradicts the nightly variation trends, whereas 1.84 d is consistent. He also processed 5,300 GEOS measurements, though the first periodogram pass had insufficient resolution. G. Letellier presented three‑colour BVR photographic results on DT Cyg and T Vul, noting issues such as “large dispersion with the green filter” and poorly defined R magnitudes.
A major session concerned 1 Persei, previously suspected of flickering. New information from Kurtz (1977) indicated it is “a probable, though peculiar, eclipsing star.” Actions were defined, including re‑analysis of 1975 photoelectric data and a possible 1978 campaign. A. Gaspani presented orbital studies of VV Ori, NN Cep and PP Lac, showing that PP Lac’s light curves could be explained by eclipses.
C. Romoli discussed period variations in CY Aqr and DY Peg. He argued that the O–C diagram of CY Aqr could be fitted by “a parabola plus a sinusoid,” though participants noted this was not demonstrably superior to earlier interpretations. Several studies of semi‑regular variables were also summarised.
G. Troispoux and A. Figer presented results from the 1977 RL 1 CVn campaign, including the first application of the “ppm effect” correction. Light curves showed hints of a 3‑hour structure but were insufficient to confirm variability. Photoelectric measurements obtained during the symposium showed a shallow minimum, possibly atmospheric or intrinsic.
The symposium also reviewed the GEOS observing programme. Changes included dropping V Vul among RV Tauri stars and reopening α² CVn stars to free observation. Delta Scuti observing was judged impractical outside summer camps, leading to a reduced routine list. Methods of calculation, including UNICYCLE and orbital‑solution software, were discussed, as well as the need to avoid “standard‑deviation by slices,” described as “an absurdity.”
General topics included carbon stars, multicolour photometry, campaign planning, and translation issues. The meeting concluded with plans to hold the 1979 symposium again in Marly.