Papers and preprints about light pollution

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Night sky brightness at sites from DMSP-OLS satellite measurements

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We apply the sky brightness modelling technique introduced and developed by Roy Garstang to high-resolution satellite measurements of upward artificial light flux carried out with the US Air Force Defense Meteorological Satellite Program Operational Linescan System and to GTOPO30 (a global digital elevation model by the US Geological Survey’s EROS Data Centre) digital elevation data in order to predict the brightness distribution of the night sky at a given site in the primary astronomical photometric bands for a range of atmospheric aerosol contents. This method, based on global data and accounting for elevation, Earth curvature and mountain screening, allows the evaluation of sky glow conditions over the entire sky for any site in the world, to evaluate its evolution, to disentangle the contribution of individual sources in the surrounding territory and to identify the main contributing sources. Sky brightness, naked eye stellar visibility and telescope limiting magnitude are produced as three-dimensional arrays, the axes of which are the position on the sky and the atmospheric clarity. We compare our results with available measurements.

The first world atlas of the artificial night sky brightness

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We present the first World Atlas of the zenith artificial night sky brightness at sea level. Based on radiance calibrated high resolution DMSP satellite data and on accurate modelling of light propagation in the atmosphere, it provides a nearly global picture of how mankind is proceeding to envelope itself in a luminous fog. Comparing the Atlas with the U.S. Department of Energy (DOE) population density database we determined the fraction of population who are living under a sky of given brightness. About two thirds of the World population and 99% of the population in US (excluding Alaska and Hawaii) and EU live in areas where the night sky is above the threshold set for polluted status. Assuming average eye functionality, about one fifth of the World population, more than two thirds of the US population and more than one half of the EU population have already lost naked eye visibility of the Milky Way. Finally, about one tenth of the World population, more than 40% of the US population and one sixth of the EU population no longer view the heavens with the eye adapted to night vision because the sky brightness.

Moonlight without the moon

Light pollution, the alteration of the natural light levels in the night environment produced by man-made light, is one of the most rapidly increasing threats to the natural environment. The fast growth of the night sky brightness due to light pollution not only is damaging the perception of the starry sky but it is silently altering even the perception of the moonlight nights by mankind. The cyclic alternation between the new moon's dark sky with thousand of stars and the moonlight sky, less dark but always full of stars among which our satellite moves, is rapidly changing toward a perennial artificial moonlight due to the man-made light wasted in the atmosphere. The moon periodically will appear inside the same perennially luminous sky from which stars will be almost disappeared. Here we present a map showing "artificial moonlight" levels in North America and some statistical results.

Blinded by the light

New Scientist presented a news about our World Atlas of the sea level artificial night sky brightness from Cinzano, P., Falchi, F., Elvidge 2001, Monthly Notices of the Royal Astronomical Society, 328, 689-707.

Naked eye star visibility and limiting magnitude mapped from DMSP-OLS satellite data

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We extend the method introduced by Cinzano et al. (2000a) to map the artificial sky brightness in large territories from DMSP satellite data, in order to map the naked eye star visibility and telescopic limiting magnitudes. For these purposes we take into account the altitude of each land area from GTOPO30 world elevation data, the natural sky brightness in the chosen sky direction, based on Garstang modelling, the eye capability with naked eye or a telescope, based on the Schaefer (1990) and Garstang (2000b) approach, and the stellar extinction in the visual photometric band. For near zenith sky directions we also take into account screening by terrain elevation. Maps of naked eye star visibility and telescopic limiting magnitudes are useful to quantify the capability of the population to perceive our Universe, to evaluate the future evolution, to make cross correlations with statistical parameters and to recognize areas where astronomical observations or popularisation can still acceptably be made. We present, as an application, maps of naked eye star visibility and total sky brightness in V band in Europe at the zenith with a resolution of approximately 1 km.

Lights go on all over Europe

The artificial night sky brightness mapped from DMSP Operational Linescan System measurements

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We present a method to map the artificial sky brightness across large territories in astronomical photometric bands with a resolution of approximately 1 km. This is useful to quantify the situation of night sky pollution, to recognize potential astronomical sites and to allow future monitoring of trends. The artificial sky brightness present in the chosen direction at a given position on the Earth's surface is obtained by the integration of the contributions produced by every surface area in the surrounding. Each contribution is computed based on detailed models for the propagation in the atmosphere of the upward light flux emitted by the area. The light flux is measured with top of atmosphere radiometric observations made by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System.
We applied the described method to Europe obtaining the maps of artificial sky brightness in V and B bands.

The artificial sky brightness in Europe derived from DMSP satellite data

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We present the map of the artificial sky brightness in Europe in V band with a resolution of approximately 1 km. The aim is to understand the state of night sky pollution in Europe, to quantify the present situation and to allow future monitoring of trends.
The artificial sky brightness in each site at a given position on the sky is obtained by integration of the contributions produced by every surface area in the surroundings of the site. Each contribution is computed taking into account based on detailed models the propagation in the atmosphere of the upward light flux emitted by the area and measured by the Operational Linescan System of DMSP satellites. The modelling technique, introduced and developed by Garstang and also applied by Cinzano, takes into account the extinction along light paths, a double scattering of light from atmospheric molecules and aerosols, Earth curvature and allows to associate the predictions to the aerosol content of the atmosphere.

Mapping the artificial sky brightness in Europe from DMSP satellite measurements: the situation of the night sky in Italy in the last quarter of century

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We present a project to map the artificial sky brightness in Europe in the main astronomical photometrical bands with a resolution better than 3 km. The aim is to understand the state of night sky pollution in Europe, to quantify the present situation and to allow future monitoring of trends. The artificial sky brightness in each site at a given position on the sky is obtained by the integration of the contributions produced by every surface area in the surroundings of the site. Each contribution is computed taking in account the propagation in the atmosphere of the upward light flux emitted by the area and measured from DMSP satellites. The project is a long term study in which we plan to take in account successively of many different details in order to improve the maps. We present, as a preliminary result, a map of the V-band artificial sky brightness in Italy in 1998 and we compare it with the map obtained 27 years earlier by Bertiau, Treanor and De Graeve. Predictions for the artificial sky brightness within the next 27 years are also shown.

The Propagation of Light Pollution in Diffusely Urbanised Areas

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The knowledge of the contribution b_d(d) to the artificial sky luminance in a given point of the sky of a site produced by the sources beyond a given distance d from it is important to understand the behaviour of light pollution in diffusely urbanized areas and to estimate which fraction of the artificial luminance would be regulated by norms or laws limiting the light wasted upward within protection areas of given radii.
I studied the behaviour of b_d(d) constructing a model for the propagation of the light pollution based on the modelling technique introduced by Garstang which allows to calculate the contribution to the artificial luminance in a given point of the sky of a site of given altitude above sea level, produced by a source of given emission and geographic position. I obtained b_d(d) integrating the contribution to the artificial luminance from every source situated at a distance greater than d. I also presented an analitical expression for b_d(d) depending mainly from one parameter, a core radius, well reproducing model's results.
In this paper I present the results for b_d(d) at some Italian Astronomical Observatories. In a diffusely urbanised territory the artificial sky luminance produced by sources located at large distances from the site is not negligible due at the additive character of light pollution and its propagation at large distances. Only when the core radius is small, e.g. for sites in the inner outskirts of a city, the sky luminance from sources beyond few kilometers is negligible. The radii of protection zones around Observatories needs to be large in order that prescriptions limiting upward light be really effective.

The Artificial Sky Luminance And The Emission Angles Of The Upward Light Flux

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The direction of the upward light emission has different polluting effects on the sky depending on the distance of the observation site. We studied with detailed models for light pollution propagation the ratio b_H/b_L, at given distances from a city, between the artificial sky luminance b_H produced by its upward light emission between a given threshold angle \theta_0 and the vertical and the artificial sky luminance b_L produced by its upward light emission between the horizontal and the threshold angle theta_0. Our results show that as the distance from the city increases the effects of the emission at high angles above the horizontal decrease relative to the effects of emission at lower angles above the horizontal. Outside some kilometers from cities or towns the light emitted between the horizontal and 10 deg is as important as the light emitted at all the other angles in producing the artificial sky luminance. Therefore the protection of a site requires also a careful control of this emission which needs to be reduced to at most 1/10 of the remaining emission. The emission between the horizontal and 10deg is mostly produced by spill light from luminaires, so fully shielded fixtures (e.g. flat glass luminaires or asymmetric spot-lights installed without any tilt) are needed for this purpose.

The growth of light pollution in North-Eastern Italy from 1960-1995

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I studied the growth rate of light pollution in the Veneto plain (Italy) analyzing archive measurements of sky brightness obtained in V, B and R bands at the Ekar Astronomical Observatory and at the Asiago Astronomical Observatory in the period 1960-1995. The light pollution in the last 35 years has increased exponentially. Assuming a constant annual increase from 1960 to 1995, the mean annual increase results of 10 percent per year. In the period 1990-1996 at the Observatory sites the strong increase of the artificial sky brightness was hidden by the decrease of the natural sky brightness due to the decrease of airglow emission produced by the sun activity going to its minimum but in the next 5 years the artificial sky brightness and the increasing airglow emission will sum producing a rapid growth of the sky brightness.

Modelling light pollution from searchlights

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I analyzed with a simple double scattering model the artificial sky luminance produced by the light pollution coming from an advertising searchlight. I evaluated both the artificial luminance produced by direct illuminance of atmospheric particles and molecules on the line-of-sight and that produced by light scattered once. I take in account the height above sea level of the observing site and the orientation of the beam.

Maps of artificial sky brightness and upward emission in Italy from DMSP satellite measurement

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We obtained the map of the zenith brightness of the night sky in Italy. The artificial sky brightness in each site is computed by integration of the contributions by each unitary area of surface obtained by applying a propagation function to the upward emission of the area as obtained from DMSP satellite night-time images. We also evaluated the emission versus population relationship comparing the relative emissions of a number of cities of various populations.

The night sky in the World Home Page

Scientific papers and preprints on-line about light pollution

Night sky brightness at sites from DMSP-OLS satellite measurements

download PDF (215Kb)

The first world atlas of the artificial night sky brightness

download PDF (650Kb)

Moonlight without the moon

Blinded by the light

Naked eye star visibility and limiting magnitude mapped from DMSP-OLS satellite data

download PDF (1.5Mb)

Lights go on all over Europe

The artificial night sky brightness mapped from DMSP Operational Linescan System measurements

download PDF (1.3MB)

The artificial sky brightness in Europe derived from DMSP satellite data

download preprint as zipped PS (1.6MB)

Mapping the artificial sky brightness in Europe from DMSP satellite measurements: the situation of the night sky in Italy in the last quarter of century

download zipped PS (174KB) download PDF (142KB)

The Propagation of Light Pollution in Diffusely Urbanised Areas

download PS (1.1MB)

The Artificial Sky Luminance And The Emission Angles Of The Upward Light Flux

download PS (267KB)

The growth of light pollution in North-Eastern Italy from 1960-1995

download PS (1.8MB)

Modelling light pollution from searchlights

download PS (459KB)

Maps of artificial sky brightness and upward emission in Italy from DMSP satellite measurement

download PS (1MB)