ASTRO LOCATIONS
Expedition of Dark Sky Slovenia to Lastovo Island, Croatia - May 2008
report prepared by Herman Mikuž and Andrej Mohar
During the April. 30. - May 4, 2008, a group of DS Slovenia members visited Island Lastovo in southern Adriatic. The aim of visit was to check the quality of night sky over Lastovo and verify it by obtaining images and instrumental measurements.
Since the island is far away from large urban areas and with population of only around 800, we expected exceptionally dark night sky. In September 2006, Lastovo and surrounding islands were designated the Lastovo Archipelago Nature Park by Croatian Parliament.
Site Location: southern Adriatic Sea, Long. 16o52' East, Lat. +42o45' North. Observing site is situated on a heliodrome at an altitude 400 m with clear horizon almost in all directions. The maximum obstructions are about 5 degrees toward the North and West. From NE to SW the visibility is down to the sea line and due to significant altitude, even a bit below the mathematical horizon. Unfortunately there are floodlights of several kilowatts near the observing site which need to be switched off for undisturbed observations.
Access from Ljubljana (Slovenia): distance Ljubljana - Split is 500 km (5-6 hours by car), distance from Split to Lastovo is 90 km or 4-5 hours by car ferry. Complete journey last about 11 hours.
Nearest cities and main artificial light sources
Split, population 220.000 and rest of Dalmatian Coast with developing tourist centers. Fortunately far away and hidden by islands in between. Islands Korčula, Hvar, Brač have only few smaller towns. They are more than 20km away. Dubrovnik, about 100km away.
Italian Adriatic coast (Bari) is 180 km away. Surprisingly, outside lighting installations were clearly visible with binoculars on May 4th morning!
Please note that all photos are unprocessed at all - just downloaded jpeg's from DSLR camera and displayed here. Raw images were also obtained as well as dark and flat frames. They will be processed and displayed here as soon as possible. All images are copyrighted. They may be used for non commercial purposes, providing that credit is given to authors: H. Mikuž and A. Mohar, Dark Sky Slovenia.
| Results of night sky monitoring on May 1, 2008 |
| Weather conditions | Southern wind at about 50km/h |
| Sky brightness with Unihedron SQM | 21.80 | at 21h30UT | average of 6 measurements |
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| Unprocessed 180 second exposure obtained at 20h52UT from a fixed tripod. Camera Canon 5D at ISO 1000, 8mm, f/3.5 Sigma fisheye lens. Clouds over the NW, N and NE horizon indicate the sources of light pollution along the Dalmatian coast and islands north of Lastovo. |
| Results of night sky monitoring on May 3, 2008 |
| Weather conditions | Calm and clear. Good seeing! |
| Sky brightness with Unihedron SQM | 21.75 | at 0h30UT | average of 5 measurements |
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| Unprocessed 180 second unguided exposure obtained at 0h34UT from a fixed tripod. Camera Canon 5D at ISO 1000, 8mm, f/3.5 Sigma fisheye lens. North is up, East to the left. Illuminated clouds and skyglow over the NW, N and NE horizon indicate the sources of light pollution along the Dalmatian coast and islands north of Lastovo. The sky is very dark in other directions. |
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| Unprocessed 180 second guided exposure obtained at 1h06UT with Canon 5D camera at ISO 1000 and 8mm, f/3.5 Sigma fisheye lens. North is up, East to the left. Illuminated clouds and skyglow over the NW, N and NE horizon indicate the sources of light pollution along the Dalmatian coast and islands north of Lastovo. The sky is very dark in other directions. |
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| Unprocessed 300 second guided exposure obtained at 1h16UT (start) with Canon 5D camera at ISO 1000 and 8mm, f/3.5 Sigma fisheye lens. North is up, East to the left. Illuminated clouds and skyglow over the NW, N and NE horizon indicate the sources of light pollution along the Dalmatian coast and islands north of Lastovo. The sky is very dark in other directions. |
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| Unprocessed 180 second guided exposure of our Galaxy center in Sagittarius. Image was obtained at 2h01UT (start) with Canon 5D camera at ISO 1000 and 50mm, f/3.5 Asahi Pentax lens. North is up, East to the left. |
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| Unprocessed 180 second unguided exposure of Milky Way over the Adriatic Sea. Image was obtained at 0h15UT (start) with Canon EOS 20D camera at ISO 1600 and 8mm, f/4 Peleng fisheye lens. North is up, East to the left. Reflections of planet Jupiter and even Sagittarius star cloud are clearly visible in the sea. Such reflections are visible only at very dark locations! The skyglow on left is from town Dubrovnik, 100 km away. There are only traces of skyglow sources toward the S-SW direction, coming from Bari (180 km) and rest of Italian coast on the other side of Adriatic. |
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| The morning dawn scene at Lastovo heliodrome after the successful observing session. Tha last quarter Moon is just rising over the Island Korčula in far distance. |
| Results of night sky monitoring on May 4, 2008 |
| Weather conditions | Strong NW wind. Very clear and good seeing. |
| Sky brightness with Unihedron SQM | 21.65 | at 1h00UT | average of 5 measurements |
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| Unprocessed 180 second guided exposure of Milky Way over the Adriatic Sea. Image was obtained at 0h56UT (start) with Canon EOS 20D camera at ISO 1600 and 8mm, f/4 Peleng fisheye lens. Reflections of planet Jupiter and even Sagittarius star cloud are again clearly visible in the sea. Such reflections are visible only at very dark locations! The skyglow on left is from Dubrovnik, 100 km away. Skyglow sources toward the S-SW direction, coming from the Italian coast are clearly visible, although they are about 180 km away. |
| Rimska cesta posneta 4. maja 2008 iz otoka Lastovo s fotoaparatom Canon EOS 20D in 8mm f/4 vsenebnim objektivom pri ISO 1600. Slika je zložena iz dveh 3-minutnih zaporednih posnetkov. Nebo nad Lastovom je izjemno temno zato se v morju vidi odboj Jupitra in celo odboj svetlobe iz središča naše Galaksije v ozvezdju Strelca. Izjemen prizor, ki smo mu lahko priča malokje, morda le na Lastovu! Čeprav je Lastovo sredi Jadranskega morja in daleč naokrog ni večjih naselij pa je na posnetku jasno vidno svetlobno onesnaženje, ki prihaja iz 100 km oddaljenega Dubrovnika (vzhodno obzorje) ter skoraj 200 km oddaljene italijanske obale (jugozahodno obzorje). Dokaz, da svetloba iz nezasenčenih svetilk onesnažuje nebo stotine kilometrov daleč. |
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| Unprocessed 300 second guided exposure of Milky Way over the Adriatic Sea. Image was obtained at 1h21UT (start) with Canon 5D camera at ISO 1000 and 24 mm, f/4 lens. Reflections of planet Jupiter and Sagittarius star cloud are clearly visible in the sea. Skyglow sources toward the S-SW direction are located along the Italian coast, about 180 km away. |
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| Unprocessed 180 second guided exposure obtained at 1h51UT (start) with Canon 5D camera at ISO 1000 and 8mm, f/3.5 Sigma fisheye lens. North is up, East to the left. Illuminated clouds and skyglow over the NW, N and NE horizon indicate the sources of light pollution along the Dalmatian coast and islands north of Lastovo. Traces of skyglow are visible toward the Italian coast. |
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| Unprocessed 180 second guided exposure obtained at 2h07UT (start) with Canon 5D camera at ISO 1000 and 8mm, f/3.5 Sigma fisheye lens. North is up, East to the left. The camera was shifted toward the south to bring out the scenic view of Sagittarius star clouds and omit light polluted sky from Dalmatian coast. The sky in NE direction is already brighter due to dawn. |
| Night sky comparison Lastovo - Črni Vrh Observatory |
By using the same camera setup and settings, we obtained the all-sky images from Črni Vrh Observatory in Slovenia just 3 days after arrival from Lastovo and compared them. Results are displayed below.
| Location | Lastovo | Črni Vrh Observatory |
| Date/Time | May 4th, 1h00UT | May 7th, 1h15UT |
| Sky brightness with Unihedron SQM | 21.65 | 21.25 |
| Lastovo, May 4 2008 at 1h51UT | Črni Vrh Observatory May 7, 2008 at 1h38UT |
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| 3-min@ISO 1000 | 3-min@ISO 1000 |
Although the sky at Črni Vrh is relatively dark for continental Europe conditions (SQM = 21.1 - 21.3 magnitude), the difference in sky brightness is surprisingly high. It seems even larger than measured with SQM because there are bright areas of strong light pollution over most of horizon. Especeally East (Ljubljana) and W-SW area is badly polluted from densly populated region Friuli in NW Italy, some 50 km away. However these areas of sky are too low to be measured with Unihedron SQM. We may therefore conclude that the difference in global LP between Lastovo and Črni Vrh is even higher than measured with SQM. The skyglow near the horizon is particularly interefering observations of objects and sky regions at low elevations as we can see on images of Sagittarius star cloud, displayed below.
Also note that typical integration times with Unihedron SQM were 5-6 seconds at Črni Vrh, while on Lastovo lasted twice longer (11-12 seconds).
| Lastovo, May 4 2008 at 1h51UT | Črni Vrh Observatory May 7, 2008 at 1h38UT |
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| 3-min@ISO 1000 | 3-min@ISO 1000 |
Conclusions and suggestions for outside lighting improvements on Lastovo island
Although our night sky monitoring on Lastovo was limited to only three nights, there is strong evidence that the sky is very dark, no doubt one of the darkest in Europe. Some light pollution is arriving from urban areas in Dalmatian and Italian coast as well as from towns/villages on Lastovo and Korcula. Because of growing tourism, state and local authorities should consider to protect this nice location from LP in future. Action should be undertaken on two levels: if Croatia will adopt similar law as Slovenia (zero emission over the 90o), the LP will be efficiently controlled. A less effective possibility would be to adopt the law in local Lastovo commune. This would at least reduce emission from local unshielded light sources. Most of outside lighting in Lastovo, Ubli, Skrivena Luka and Pasadur is very old and need to be replaced in near future. Now it is nice opportunity to choose and set up fully shielded lamps and help to preserve this excellent location to future generations. Lastovo has a good potential to became a European center of astro tourism which is not limited only to summer but would be of interest all over the year.
Acknowledgement
Dark Sky Slovenia would like to thank to Lucija Kapiteli, director of Lastovo Natural Park for her invaluable assistance during our visit that lead to successful completition of our observing program.
