Map of Arkhyz gorge and regional center Zelenchukskaya

Fragment of tourist map 'Karachai-Cherkessian Republic', KartInform-RosKartographia, Pyatigorsk, 2006.

Light pollution sources.

The nearby regional center, kazak village Zelenchukskaya is located at the direct visibility from the BTA observational sight at the distance of 25 km. Views of village at night are shown in the Fig. 8. The negative image taken at night is superimposed on daytime image in winter at the Fig. 9. Other light sources are identified in this picture, too. They are Dausuz the community where the hydroelectric power station is built recently; the kazak village Kardonikskaya, and communities of Zhako and Ali-Berdykovsky. RATAN-600 radio telescope, and Zelenchuk radio observatory are also light sources located in direct visibility. Since 2006 no essential changes in the city lights are noted excluding indeed the dam of power station, sometimes, it is illuminated with 15 powerful uncovered lamps. In Zelenchukskaya and Dausuz, one may count about 260 street lamps at the direct visibility. Here, in the vast scale one can check these counts.

Figure 8. Photos of kazak village Zelenchukskaya and surrounding communities located at the direct visibility from BTA observational sight taken at night in three dates between November 2006 and January 2008. On 2007 February 17, the lighting of power station dam in Dausuz was switched on (marked by an arrow). The strongest sodium lines are installed near the power station in Dausuz.

Figure 9. Photo of Zelenchuk village, and other surrounding communities taken from the observational sight of SAO in the winter daytime, the negative night photo is superimposed. General light sources are identified.

The astronomers' village Nizhnyj Arkhyz located at the distance of 3.5 km is the nearest locality to BTA. One can found that the astronomers' village is 7.9 times closer to BTA than the center of Zelenchukskaya using only this map and a ruler. As illumination by a light source is proportional to squired distance to it, the interference from one lamp in the astronomers' village is equal to 62 lamps in Zelenchukskaya (7.92)! The astronomers' village does not located on the direct visibility from the BTA sight, but the light of its illumination scatters easily in the air over the telescope. So, the only 4 lamps are enough to give the same effect as that one of 260 lamps in Zelenchukskaya. Here we present the facts which give the evidence that namely the astronomers' village is now the main source of light pollution of the sky for BTA. Partly, we use the method by International Dark-Sky Association to check the efficiency of street lights photographing the light sources in the fog. The following are such photos with the explanations.

Figure 10. Nighttime photo in the fog (left), and daytime photo (right) of the village. View from the north from refuelling station. Evidently, the light of lamps spreads easily upwards. Effect is strongest inspite of absence the snow cover at the time of taking this photo.

Figure 11. Nighttime photo in the fog (left), and daytime photo (right) of village from south-east. Snow cover is absent. Power glow is the light of lamps scattered on the fog drops and spreading easily upwards.

Figure 12. Economic parts and garage of SAO in the astronomers' village. Nighttime view from Zelenchukskaya - Arkhyz road.

Figure 13. Powerful glow-discharge lamp of SAO firehouse is installed so as its light is going just in the direction to BTA to be of largest harm for the observations. Similarly, two other lamps are installed on the buildings of boiler-house and storehouse for fuel. Near the control pass unit, such a lamp is installed vertically and directed opposite of BTA but it illuminates large field and surrounding hills. With the snow cover, all this light is scattered upwards.

Night sky spectrum of the Special Astrophysical Observatory.
Observations of relative intensities of HgI and NaI
Characteristics of interference due to light pollution at SAO observational sight.
Light pollution sources-1.
Light pollution sources-2.
Results and conclusions.
Continued. Monitoring the situation.