MARCH 2005









              SEEING-GR is an ambitious new project aiming in measuring and calculating a median value of the true astronomical seeing (the turbulence of the atmosphere) in Greece. The method we are using is a modification of the original DIMM method first suggested by ESO (A&A 227, 294-300, 1990. M. Sarazin and F. Roddier), which enjoys global recognition and is rightfully considered to be the most trustworthy method of measuring the seeing. Because the collection of data from all over Greece cannot be undertaken from one person alone or even a single group SEEING-GR is mostly addressed to amateur astronomers inhabiting both remote places and the metropolitan centres (even in Athens and Thessaloniki), as well. This project (measuring the seeing of a whole country) is unique and has never been done before. Greece is one of the privileged countries as clear skies can be found throughout the year in most places, but also (and most importantly) because it has many well-grounded and adequately equiped amateur astronomers.

              The data for the project will be gathered from amateur astronomers exclusively and will afterwards be reduced in the Observatory of Thessaloniki. For these reasons participation in SEEING-GR will ONLY be allowed to amateurs who meet some basic requirements:


1)      Adequacy of Astronomical Equipment: A telescope, both refractor or reflector at least 6 wide, with motor drive for the hour angle and a CCD camera (and NOT a Web-Cam, various Digital Cameras, single frames from Video-Cams etc) is to be considered as adequate astronomical equipment. Variations from the above mentioned equipment (especially Web-Cams) are currently being tested in the Observatory to find out if they can be used in this project. Finally, a special mask (cardboard-made or plastic), which anyone can make, and of cource a PC are also needed. 

2)      Because the data reduction requires special software, which has been written in the Observatory for this specific purpose, the data send by each amateur astronomer should have some consistency, thus limiting the error possibility and enabling the software to run without problems. That is why anyone wishing to participate in the project should conduct the observations in the way described inb this guide.


This is what is needed from someone to take part in SEEING - GR. Possible participants should fill out the sheet following  in the next page and e-mail it to: (please send only the filled sheet):










First Name    :

Last Name  :

Data aquisition region (geographical coordinates) longitude  :

                                                                             latitude  :

Full Postal Address (for software posting) :



Do you have MaxIm DL

for Windows installed?                                                                                YES                   NO


e-mail         :






FOCAL LENGTH    (cm) :


CCD CAMERA  (model)  :


Pixel size (m) :



              By submitting the application (and after it is accepted) you will recieve a serial No (ID), by e-mail, which will be used by the central PC, when reducing the data from each observer (the ID mailing can take up to some days) and also a file named dimm.vbs, which is the script being used for  automatically taking and saving the data. Furthermore, observers will recieve (in the postal address stated) a cd-rom with the astronomical programm (for Windows) MaxIm DL which should be installed in the observer's PC (if of course the observer hasnt got it already). After that observers are asked to send their data to the Observatory of Thessaloniki.




              Before we can start a seeing measurement we must have an appropriate DIMM-mask for the telescope we are using. A DIMM-mask is nothing more than a simple cardboard- or plastic mask with two circular holes. The mask is placed in front of the telescope, instead of its cover (picture 1).


Picture 1: A Celestron GN-8, one of the telescopes used by the Observatory of Thessaloniki for seeing measurments in the Holomon Astronomical Station (Chalkidiki, Greece). The DIMM-mask and the CCD SBIG ST-4 can also be seen in the picture.


The holes should be about 5-8 cm wide and their distance about 15-25 cm, depending on the telescope (see Table 1). By targeting a star and keeping it slightly out of focus we will  have 2 images of this star.



Telescope diameter (inch)

Hole distance (cm)

Hole diameter (cm)




















              We then target a bright star near the zenith and mount the CCD on the telescope. We first take some frames (manually, without using the dimm.vbs script) for testing, calibrations and making sure the star is inside the camera's field. It is clear that these frames shouldnt be saved. We bring the telescope out of focus in such a manner so that the images of the star have a distance of about 10-15 pixels. It would be better if we took a series of frames while defocusing the telescope (again without saving them).

              When the telescope is set we create a new folder c:/dimm/data (in any case the script has a reminder) where the data is going to be saved. Then we just double-click on the dimm.vbs file and the camera will begin taking a series of frames and saving them in the folder we created. We MUST NOT forget to write down the exact time the observations began (official Greek time, not UT). When the camera is done and the script is over we MUST NOT forget to write down the time again. Every participants can send a CD with the data by post in the following address:


Professor John H. Seiradakis 

Department of Physics, Section of Astronomy, Astrophysics and Mechanics

Aristotle University of Thessaloniki





If a participant wishes so, he can first gather data for 2-5 nights (consecutive or not) and then send it to the Observatory, so as to avoid the discomfort of posting CDs every day. Apart from the data, the CD MUST also have a results.txt file containing:




If some of the information is missing or is not complete the data CANNOT be reduced. If more then one seeing measurments are made in a single night (for example in the begining, the middle and at the end of the night and not throughout) you just have to repeat the whole procedure. However, you must not forget to move the data of the previous observation in a different folder, otherwise the new ones will overwrite the old. A new results.txt file is required every time you run the script.




Open the folder ''SEEING_GR/MAXIM_DL/DISK'' and double-click on the 'SETUP' file. In the following dialog box a password will be requested, which can be found in the  'serial_number' file inside the 'SEEING_GR/MAXIM_DL' folder.



Because seeing measurments are very exact and sensitive, they can be affected by many factors. DO NEVER use another observers' script. The scripts are specifically written for each one's telescope and equipment. Your data will NOT be correct if you use a different script. Furthermore, however good and broad you knowledge of programming may be DO NOT attempt to alter the code, because the reduction code will give complety incorrect results! If you have any ideas or suggestions for the code or anything else, it's best if you first inform the Observatory.


Each observer can ask (by e-mail) for a seeing graph of the areas covered by the project anytime, but should also allow a couple of days before recieving the graph. In case of a scientific publication the Observatory will mention the names of everyone who participated and help in the process.



Observatory of  Thessaloniki

Aristotle University

March 2005





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