Report on the light pollution at a site - summary
Site: / Mountain hotel st. Andrija - Vis islandSite description: / On the top of the st. Andria hill resists the mountain hotel st. Andrija. In from of the hotel is a clearing, approx. 30x20 m in size. LP measurements were done in the middle of the clearing.
The site is located about 20 min. drive form the town Vis, at the beginning on a paved road (4337 m) and after dat on a gravel road (2339 m). The last 356 m are passable only to four wheel drive vehicles. Cars can be parked before this section of the road (approx. 4 parking places).
The shortest walking way is by a well labelled montanier track that is 3215 m long.
Geographic coordinates: / = 43o 3' 13'' / = 16o 11' 0'' / h= 267 m / WGS-84
Date: / 17.-18.5.2012.
Time: / 22:15 - 23:40 / Summer time
Local time: / 21:15 - 22:40
Meteorological conditions: / Humid, foggy, 12 oC, strong SW vind, thin cirrus
Day photography / Yes / Panorama. Yes
Limiting magnitude: / -
Bortle class: / 3
SQML measurements: / Yes / Zenith:Yes / Detailed: No
Sky brightness at the zenith: / 21,39 / Average of 4 measurements
21,44 / Best value
All-sky photography: / Yes / Directions owerlay: Yes
Isophotes / Yes
Observer: / Željko Andreić
Data reduction by: / Željko Andreić
Report version: / 2.2
Version date: / 18.6.2012.
Checked by: / Željko Andreić
Conclusions:
Taking into account bad meteorological conditions, the measurements reveal exceptionally good location with almoust naturally dark sky. With high humidity and a lot of aerosols a small light pollution dome of town Vis can be seen near the north-east horizon, and in a distance light pollution produced by towns Split, Hvar and several smaller settlements can be seen. At heights above 20 degrees all that light pollution is already fainter than the zodiacal light, and the remaining sky is naturally dark.
Report on the light pollution at a site - naked eye assesment
The light hase is present in the atmosphere, the air is humid and quite cold for this part of the year (12 0C).Near the horizon, in general direction of the Vis town, which is located directly under the st. Andrija hill, the light pollution from it can be seen. In distance the LP domes of towns Split, Hvar and several smaller settlements can be observed. At heights above 20 degrees all that light pollution is already fainter than the zodiacal light, and the remaining sky is naturally dark.
After the end of astronomical dusk, the weak zodiacal light can be seen, and is confirmed by photography, and the whole sky dome, except areas near the horizon in directions of larger settlements, is dark and full of stars.
Sunset and the setting of Venus indicated a strong extinction. For instance, Venus vas barely visible at the moment of its setting.
Report on the light pollution at a site - SQM-L measurements
1. Sky brightness at the zenith
Local time / Sky brightnessmag/arcsec2
21:15 / 21,43
21:29 / 21,36
21:44 / 21,42
22:40 / 21,35
Report on the light pollution at a site - all-sky photography
Camera: / Canon EOS 1000D / Modification: / NoLens: / Sigma 2,8/4,5 / Filter: / None
ISO: / 400 / Aperture: / 2,8
Exposure: / 4 m / Dewcap: / No
Image time (local): / 22:20 / Image number: / IMG_3939.jpg
Dark frame: / No / Vignetinng correction: / No
Report on the light pollution at a site - all-sky photography
Report on the light pollution at a site - all-sky photography
Report on the light pollution at a site - the location
The clearing in front of st. Andria hotel.All measurements were taken from the middle of it.
The horizon, as seen from the middle of the clearing, is low. A large portion of it is sea horizon, which is very suitable for astronomical observing. The heights indicated at the right side of the image are approximate!
Report on the light pollution at a site - discussion
Regardless of the bad meteorological conditions at the time of assesing the site (cirrus clouds, high humidity) the night sky of the Vis island turned out to be omong the best in Croatia, and can reach Bortle class 2 in best meteorological conditions, where class 1 is the totally natural night sky, that does not exist in Europe anymore, except on high sea at least 300 km from the nearest coast. The nearest natural sky can at the moment be found in Sahara desert, or in the extreme north of the continent.
In general direction of the Vis town, which is located directly under the st. Andrija hill, the light pollution from it can be seen. In distance the LP domes of towns Split, Hvar and several smaller settlements can be observed. At heights above 20 degrees all that light pollution is already fainter than the zodiacal light, and the remaining sky is naturally dark. Only part of the horizon extending approximatelly from nort to the east is poluted in this way, the rest is naturally dark.
After the end of astronomical dusk, the weak zodiacal light can be seen, a fact tha confirms the exceptional quality of this site.
The site is suitable for observing at night as there are no big stones or holes in the ground that could led to injuries. It can accomodate about a dozen astronomical instruments/observers at the same time. The horizon is low and partially ideal (sea surface), which increases the suitabilty of this place for amateur astronomical observations of all kinds.
It is recomended to additionaly clean the vegetation and remove all stones lager than a few centimeters and to fully level the clearing with fine gravel. Also, some measures should be taken to prevent light spill from the inside of the building onto the observing area. For instance, at observing times dim red lights could be used inside the building. Such a light would not spoil the dark adaptation of observers, and would at the same time alow other activities indoors. Alternativelly, the windows could be blinded and a double door used for going in or out the building, thus preventing bright light escaping it. In case that a larger group comes to observing, especially if they are unexperienced in observing, the clearing edge towards the steep fall should be secured by some sort of a fence, to prevent accidents on the steep.