As the peak of the summer holidays approaches, what better time than now to discover together which places in Italy have the sky with the least light pollution. Whether you want to observe with the naked eye or with a telescope, the best places of our peninsula where you can organize observation sessions to observe the spectacle of the night sky are along the Apennine area, in Alto Adige and in the central areas of Sardinia. For detailed information on the brightness of the night sky in your area, please consult the Light Pollution Atlas.
How to measure the quality of the sky
In order to measure the quality of the sky at an observing site, astronomers use the surface brightnessa quantity used to express how luminous a celestial body is per unit of angular area it occupies in the sky. Its unit of measurement is magnitudes per square arcsecondwhich gives a measure of how much light comes from a square area of the sky equal to 1 arcsecond (1/3600 of a degree). The higher this value, the less light comes from an object with an area equal to 1 arcsecond squared. Usually this value is measured at the zeniththat is, perpendicular to the observer.
Using values for different points on Earth, astronomers were able to create a scale, known as Bortle’s scalewhich assigns a value from 1 to 7 to an observing site, based on how heavy the light pollution is at that location. The best skies in the world, such as those of Paranal Hill in Chilethey have a value equal to 1 on the Bortle scale: the brightness of the night sky is around 22 magnitudes on square arcsecond. Under these skies, the Milky Way appears visible to the naked eye in all its glory and, if you are in the southern hemisphere, the Large and Small Magellanic Cloudssatellite galaxies of the Milky Way, are visible to the naked eye.
THE worse skiesthose citizenshave a Bortle scale value that varies from 6 to 9depending on whether you are in a suburban area or in a city centre: the brightness of the night sky varies from 19 at 17-18 magnitudes on square arcsecond (remember that the magnitude scale is descending: the brighter an object, the lower its magnitude). Under these skies, one goes from recognizing some constellations (suburban sky) to seeing very few stars, or in the worst case, even only the Moon.
The best places in Northern Italy
The high population density of the Po Valley makes it one of the places with the highest light pollution of Italy. In general, every urban agglomeration is an enemy of observations of the night sky, with LED lights or sodium lamps that are sometimes pointed directly upwards.
However, in northern Italy it is still possible to find places where light pollution is greatly reduced. For example, the entire area ofSouth Tyrol along the Alps that goes from Stelvio National Park at the Lavaredo Peaks presents a brightness of the night sky that is almost of a lower factor 6 to that of nearby mountain agglomerations such as Brunico or Vipiteno. Even the brightness of the night sky is 100 times lower to that of large nearby cities such as Bolzano.
These areas have a value equal to 2-3 on the Bortle scale. It is therefore possible to observe the Milky Way with the naked eye, and the number of visible stars makes it difficult for an inexperienced eye to distinguish the different constellations in the sky. In some cases it is also possible to make out the faint whitish patch of the Andromeda Galaxy.
The best places in central Italy
Even central Italy is not immune to light pollution, particularly in large cities like Rome and along the Tyrrhenian and Adriatic coasts. However, it is possible to find skies with a very good quality moving towards the Apennineswhere the Bortle scale indicates a value ranging from 4 to 5 (21.5-20.6 magnitudes per square arcsecond).
However, there is a specific point where the brightness of the night sky is decidedly better and comparable, if not better, than in the Alpine area of South Tyrol. This is the Manciano areain the province of Grosseto, where, not by chance, one of the telescopes of the Virtual Telescope project is located. This is considered the location with the best sky in mainland Italy: here the brightness of the night sky is more than a factor 100 less compared to nearby urban agglomerations (Bortle scale 3-4), allowing for excellent astronomical observations, even professional ones.
The best places in the south and the islands
In the south, Apulia and Campaniaparticularly in the coastal area, are heavily affected by light pollution. It is necessary for the inhabitants of these areas to move either towards the Molise in the area between Castel di Sangro and Agnone, or along the southern tip of the Apennines which touches the provinces of Avellino and Basilicata. In these areas, the Bortle scale has values around 4-5. In Calabria, however, it is possible to go down to values of the Bortle scale equal to 3 in the area of Sila and Pollino National Parks.
The two largest islands of our country present two very different scenarios in terms of light pollution. In Sardinia instead we find again some among the best skies in ItalyThis is the area of the Gulf of Orosei and Gennargentu National Park which present values on the Bortle scale that can even drop to around 2-3. Sicily, on the other hand, has heavy pollution in almost every area of the region, with the exception of Nebrodi Regional Park (Bortle scale equal to 4-5).
