The Variable astrocamp is a game. The participants play a role of researches solving the tasks announced by the organizers. At the end of the astrocamp they present the results on the improvised scientific seminar.

Following are typical research task used to be solved. The actual offer varies each year depending mainly on available instruments and supervisors.

**Extinction Coefficients**Description: To determine the extinction coefficients of 1^{th}and 2^{nd}order for the locality of Astronomical Observatory at Kolonica Saddle. Compare the results from different nights. Look for correlations between meteorological data (humidity, air pressure, temperature). Use the CCD data collected by other researchers in the astrocamp or use archival data of the observatory. Researcher of this task don’t need to make his own observations during the night. Therefore may be available to researchers who collects visual observations.**Transformation Coefficients***Description*: To acquire several points on light curves of semiregular and symbiotic variable stars included in the observing program MEDÚZA in different photometric filters. Transform the CCD measurements into the standard photometric system using previously determined transformation coefficients. First determine the transformation coefficients of your instrument. Use the suitable standard open cluster on summer sky. IC 4665 is recommended. You need measurements in the field with good absolute photometry available. Then make your own observations of selected objects and transform data to the standard system. Make one point every night in all filters (B, V, Rc, Ic).**Semiregular and Symbiotic variable stars***Description*: To acquire several points on light curves of “MEDÚZA stars” visually. Construct the light curves using your own and archival data. Include also results from research task No. 2 to evaluate the quality of visual observations. Perform visual estimates of selected objects using Nijland-Blazhko method during all the astrocamp. For every object – one estimate per night. In addition to normal light curves try to construct folded light curves with periods from catalogs. The period can be unstable in the case of semiregular variables. Show the results of period analysis in that case.**O-C diagrams of eclipsing binaries***Description*: To construct O-C diagrams of times of minima of several eclipsing binaries. Use the data from available databases and at least one personal measurement. Make the observations with CCD camera and simultaneously organize visual observations by astrocamp participants. Compare the accuracy of the time of minima determined by both methods (CCD and visual observations). Determine CCD time of minima using Kwee & van Woerden method (software AVE) and fitting tool implemented on var.astro.cz as well. Use Kordylewski method (software Protokoly) for visual observations. Select suitable observing targets for the given night using program “POZOR”-
**O-C diagram****s****of Intermediate Polars***Description*: To construct the O-C diagram of pulse maxima connected with white dwarf rotation in the intermediate polar system. Use the data from literature and at least one personal CCD observation. Intermediate polars has asynchronous rotation. On the light curve we can see the orbital motion and spin of the primary component as well. The spin period has typically 10 – 20 minutes. So we need long observing run lasting several hours with good time resolution (max. ¼ of the spin period). One filter is sufficient. We have to subtract the orbital wave mathematically. The corresponding point in the O-C diagram you get after fitting the measured points with sinusoidal fit. All necessary mathematical operations can be done with the program “MCV”. **Binary star model***Description*: To determine the basic parameters of binary star system. Use your own CCD observations of selected eclipsing binary with four photometric filters (B V Rc Ic). It is necessary to observe at least one complete light curve (all phases). The corresponding model can be constructed using available program, for example “PHOEBE”.**Superhumps***Description*: To determine the period of superhumps of SU UMa type cataclysmic variable and its evolution during superoutburst. Use your own CCD observations of the object in superoutburst during the astrocamp. SU UMa type cataclysmic variables shows typical “humps” on the light curve. The period is usually slightly longer than orbital period of binary system. The typical value of the period is 80 – 120 minutes. It is easy to determine the period of superhumps using all night time series observation. The period evolves during the superoutburst. This tell us something about precession movement of the accretion disc. Therefore we have to observe as long as possible every night during the superoutburst.**Cepheids***Description*: To construct the folded light curves of several bright and well known cepheids based on personal visual observations. Compare your own measurements with photoelectric folded light curves from literature. Using your observations estimate the distance to observed cepheids. Compare it to the published values. The typical period of cepheid pulsation is several days. Hence you need 2 or 3 estimates per night during all the astrocamp. Use not only your own measurements but also the estimates of the other participants. The distance can be estimated using available methods.**The accuracy of visual observations***Description*: To perform visual observations of constant stars using given comparison stars. Evaluate the measurements statistically. The supervisor will give out special charts just before the start of observations. This way we want to avoid the possibility to find the correct value of constant star magnitude from a catalog. The statistic evaluation means determination of standard deviation for each observer, its dependency on star brightness and color. Use not only your own measurements but also the estimates of the other participants.**Spectroscopy of variable stars**.*Description*: To acquire low resolution spectra of different types of variable stars. Be stars, Cepheids, Symbiotic, Cataclysmic, … . Evaluate the results and explain the features on the obtained spectra (continuum, identification of absorption and emission lines).