Report on the light pollution at a site - summary
Site:
Mountain hotel st. Andrija - Vis island
Site description:
On the top of the st. Andria hill is 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.
Date:
 = 43o 3' 13''
17.-18.5.2012.
Time:
22:15 - 23:40
Local time:
21:15 - 22:40
Meteorological conditions:
Humid, foggy, 12 oC, strong SW vind, thin cirrus
Day photography
Yes
Limiting magnitude:
-
Bortle class:
3
SQML measurements:
Sky brightness at the
zenith:
Yes
Zenith: Yes
21,39
Average of 4 measurements
21,44
Best value
Geographic coordinates:
 = 16o 11' 0''
h = 267 m
WGS-84
Summer time
Panorama. Yes
All-sky photography:
Yes
Isophotes:
Yes
Observer:
Željko Andreić
Data reduction by:
Željko Andreić
Report version:
2.2
Version date:
18.6.2012.
Checked by:
Željko Andreić
Detailed: No
Directions owerlay: Yes
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
21:15
Sky
brightness
mag/arcsec2
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:
No
Lens:
Sigma 2,8/4,5
Filter:
None
ISO:
400
Aperture:
2,8
Exposure:
4m
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
N
W
E
60o
30o
0o
S
N
W
E
60o
30o
0o
S
Report on the light pollution at a site - all-sky photography
N
W
E
60o
30o
0o
Isophotes step: 20% of the
brightness at the zenith
S
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.
60o
40o
20o
0o
N
W
S
E
N
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.