Light Pollution in Puerto Rico
By Armando Caussade.Uploaded: December 31, 2004. Revised: December 31, 2004.
Light pollution is the artificial brightening of our nocturnal skies due to electrical lighting. This brightening degrades the visibility of stars and deep sky objects as to render them nearly invisible. The problem of light pollution is very widespread, affecting virtually every amateur astronomer living in an urban area today.
Due in part to the island's high population density, the effects of light pollution are particularly severe. As apparent in figure 1, Puerto Rico is indeed the brightest patch of light throughout the Caribbean, except perhaps for the large urban areas of Florida. The island's semi-rectangular shape is easily discernible since about 90% of the coastline is illuminated by artificial lighting. Figures 1 and 2 are actual nocturnal photographs of the Earth's surface, obtained by satellite missions.
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Figure 1. City lights of the Caribbean
Source: NASA/GSFC Comments: This is a segment from the Earth's City Lights map obtained from space by the DMSP mission. The rendition used here is based upon the 8,192 × 4,096 full color TIFF version, with cropping and compressing to JPEG. The original scale has been preserved. |
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Figure 2. City lights of Puerto Rico
Source: NASA/GSFC Comments: Puerto Rico, the U.S. Virgin Islands and part of the Dominican Republic from the DMSP map. This picture has been cropped from the 30,000 × 15,000 grayscale GIF version, giving the highest possible resolution from among the publicly available images. As above, the scale matches that of the original. |
In contrast to the former two pictures, figures 3 and 4 are an attempt to quantify the continuous, unsaturated levels of light scatter in the atmosphere. These levels may effectively be interpreted as the actual amount of light pollution that would be observed from the Earth's surface. Figure 3, in particular, illustrates the intense scattering of light over Florida and Puerto Rico, causing even the far-inland regions to appear flooded by light pollution.
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Figure 3. Light Pollution in the Caribbean
Source: World Atlas of Artificial Sky Brightness (see below for details) Comments: The entire Caribbean region, as well as the Bahamas and part of Florida, are visible in this image. The rendition used here is based upon the high-resolution North America chart, with cropping and compressing to JPEG. The scale is about 19% that of the original. |
http://skyandtelescope.com/printable/resources/darksky/article_84.asp
As evident from this map, the San Juan metro area—where I live—is rated at Bortle class 8, while most of the dark sites to which local amateurs have access get down to only about a Bortle class 5. The darkest sites throughout the island would in fact be those around the western interior region, with a Bortle class rating of 4.5. However, the islands of Vieques and Culebra—both of which are actually offshore townships of Puerto Rico, located at 20 km to the east of the main island—appear to lie under significantly darker skies, rated at about 4 and 3 in the Bortle scale, respectively.
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Figure 4. Light Pollution in Puerto Rico
Source: World Atlas of Artificial Sky Brightness (see below for details) Comments: Puerto Rico, the U.S. and British Virgin Islands and parts of the Dominican Republic, and Leeward Islands are shown here. This picture has been cropped from the high-resolution full color TIFF version and left to the original scale. |
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Figure 5, shown below, is a population density map of Puerto Rico. Compare this map to one above to see how closely light pollution is related to population density. San Juan is represented by the dark green patch at the northeast. The lightest shade of yellow—which is used to represent the more sparsely inhabited areas throughout the interior—corresponds to a density range starting at 62 persons per km2. According to the current (2000) U.S. census results, a total of 3.8 million people were recorded in the island, which, if averaged over a surface area of 8,800 km2, would give an overall population density of about 430 persons per km2.
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Figure 5. Population Density in Puerto Rico
Source: United States Census Bureau Comments: This map is based upon the 2000 U.S. census results. Click here to see the legend of this chart. |
The last two pictures show the actual effect of light pollution as seen from the ground. Figure 6 illustrates the lights of Mayagüez, which is Puerto Rico's third largest urban area with a population of about 100,000. Figure 7 is a photograph of the intense light scattering caused by metro San Juan, as seen from Comerío, which is a town located on the northern slopes of the Cordillera. The lights of San Juan itself are obviously merged with those of Bayamón, Guaynabo and other nearby municipalities.
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Figure 6. Lights of Mayagüez, Puerto Rico
Copyright © 1991 Carlos F. González. Used with permission.
Date: August, 1991 at approx. 12:00 AM, from 4 km N of downtown Mayagüez |
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Figure 7. Lights of San Juan, Puerto Rico
Copyright © 1990 Armando Caussade
Date: November 17, 1990 at approx. 10:00 PM, from about 25 km SW of San Juan |
The maps in the World Atlas of Artificial Sky Brightness are copyright protected. This product is being used on a non-profit basis to illustrate the extent of light pollution in Puerto Rico and surrounding areas. The Atlas may be found at http://www.lightpollution.it/dmsp/.
Credit: P. Cinzano, F. Falchi (University of Padova), C. D. Elvidge (NOAA National Geophysical Data Center, Boulder). Copyright Royal Astronomical Society. Reproduced from the Monthly Notices of the RAS by permission of Blackwell Science.
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