2004 – Kolonica 12 – 21 August

First participation of Pavol A. Dubovský




43 visual times of minima for 11 eclipsing variables.

Training of color corrections in visual observing on cepheids variable. On the figure the comparison of visual and photoelectric observations from the literature is shown.


Abstract: This article describes the results of summer astronomical camps in Slovakia dedicated to variable stars observing.

I had the honor to spend the second half of August 2004 at the Astronomical Observatory of the Vihorlatská Observatory in Kolonické sedlo. First, 9 nights on the Variable expedition, which is intended for members of the local SZAA organizations in Humenne and Snina, and then another 5 nights on our “Orava” expedition, which was attended by the SZAA MO in Podbiel and some other high school students who showed their interest in astronomy by participating at the “What do you know about the stars” competition. Of those 14 nights, 8 were clear. The Variable expedition also had eclipsing binaries in its observing program. A minimum of 11 stars were observed, while the observers made a total of 536 estimates. However, I specifically devoted myself to training new techniques for visual observation of variable stars in the spirit of the methodology developed by the Argentine amateur Sebastian Otero. The essence of the method is to take into account the color indices of the stars and observe so that the result corresponds to Johnson’s V filter. Several participants from each expedition participated in the exercise. There wasn’t a complete beginner among them, so the theoretical training was over quickly. The practical exercise is that the eye must be calibrated against the color indices of the comparison stars. The observer does not acquire this ability immediately. It takes practice gained from making lots of estimates. Thus, the accuracy with which a particular observer observes gradually increases. The task of our experiment was actually to find out what kind of results a beginner will achieve during the first week.

We identified 4 well-known Cepheids as the objects of our observation: Delta Cep, Eta Aql, SU Cyg and TU Cas. Of these, the first two are observable with the naked eye. We observed the other two using a binocular. Cepheids are good for practicing a new method because they also change color during the cycle, forcing the observer to notice these changes closely. In our free time, of course, we also observed other physical variables of the stars. Mainly semi-regulars from the Medúza program. They are also mostly pretty red, so they test the observer’s ability to correct the associated effects. In total, we made 275 estimates of physical variables.


The attached images show the phase light curves of the observed Cepheids. Our measurements are compared with photoelectric data obtained from the literature.

Delta Cep and Eta Aql are great. For Delta Cep, it is somewhat complicated by the presence of a sixth-magnitude blue companion, which we cannot distinguish with the naked eye, and in addition, it is NSV star number 25915 varying from 6.10 to 6.37 V. The data are corrected assuming that the companion is 6.3 mag.

Without a deeper statistical analysis, just by looking at the curves, we can say that the data do not have an obvious systematic deviation. So we actually observed in V. With telescopic stars, the data deviated by up to 0.2 mag, with the naked eye it was better by around 0.1 mag. These variations appear to be related less to the experience of the observer than to the experience of observing the star in question. We expect that as the number of estimates increases, the deviations of individual observers will decrease. Therefore, the experiment will continue. It will continue to be observed at the Friday meetings of the MO SZAA in Podbiel and at astropractices organized by the Vihorlatská Observatory in Humenne in cooperation with the MO SZAA Snina


Young observers can be happy to have been blessed with such a great photometric detector as the human eye. All the more because they have learned to use it wisely. The goal is to improve the ability of observers to calibrate the eye, to cover light curves more densely, to expand the observation program, to learn how to process and evaluate data, and to become familiar with theoretical knowledge about Cepheids as an important landmark in the study of the universe. Of course, we do not expect any scientific results from the visual observation of Cepheids. Nor do we expect the birth of many new powerful variable star observers. However, we hope that the experience of practical measurements and the wonder of elegant mathematical interpretations will leave traces in the participants of the experiment that will serve to shape their worldview. Let them apply the acquired skills in any place where they will work in life.

The experience gained allows us to draw some lessons for the further course of the experiment, or they can serve as advice to potential followers.

  1. Better selection of stars – the main criterion for the selection of stars for the observation program was a short period. This is in order to measure the largest possible part of the light curve during the expedition. In the case of Cepheids, a short period also means a low amplitude and therefore more difficult visual observation. With year-round observation, this criterion no longer applies. We can therefore include other Cepheids in the program, suitable even for complete beginners.
  2. Observe more frequently – we did not observe often enough during the expedition. Especially in the ascending parts of the curves, we underestimated the speed of change of brightness. With these periods, it is quite possible to make an estimate even every three hours. It would also be good not to observe at once. It was necessary on the expedition because of the briefing. But in the future it will be better if observers make estimates independently of time. On the light curve, we will get random points on the timeline, and the curve will definitely be more beautiful.


We owe the opportunity to carry out the experiment mainly to the Vihorlatská Observatory in Humenne, headed by the director RNDr. Igor Kudzej. We were able to use the excellent natural and infrastructural conditions of the observatory in Kolonicke sedlo. Both expeditions were financially supported by the Children’s Foundation of Slovakia within the Children’s Hour program. Thanks also go to all the observers who participated in the experiment. Specifically, they were: Zuzana Tormová, Lenka Serdulová, Erika Pindrochová, Ján Marinič, Martin Pauco, Natália Makarivová, Veronika Sičáková, Mariana Hronovská, Jakub Labaj, Juraj Spišiak, Vladimír Svetlošák and Tomáš Zanovit.


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