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The Sky Brightness Map is based on work by Cinzano, Thiene, Italy
(1998). It is colour coded according to the Bortle scale. The
site is located in the gray area which is a rating of 2 on the
scale and has a limiting magnitude of 7.1-7.5. You can clearly
see that the chosen area is indeed the darkest available in Southern
Canada. OMI is indicated with the red circle. On May 28/29 2008
a reading of 21.82 was taken at the arae.
The map is courtesy Google Earth with the sky
Brightness Map overlaid.
Pan over the light bubbles to identify cities and towns.
Distance radii (50 km circles), pan over to identify cities.
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Color Mag.
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Bortle Class
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Sky Brightness mag/arcsec²
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Sky Brighness Artificial/Natural
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7.6 - 8.0
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1
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>21.6
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<0.01
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7.1 - 7.5
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2
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21.6 to 21.5
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0.01 to 0.11
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6.6 -7.0
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3
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21.5 to 21.3
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0.11 to 0.33
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6.3 - 6.5
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4
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21.3 to 20.8
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0.33 to 1.0
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6.1 - 6.3
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5
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20.8 to 20.1
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1.0 to 3.0
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5.6 - 6.0
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6,7
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20.1 to 19.1
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3.0 to 9.0
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5.0 - 5.5
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8
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19.1 to 18.0
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9.0 to 27.0
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<4.5
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9
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<18.0
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>27.0
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Sky brightness table
The sky brightness map is colour coded to represent the apparent
sky brightness. White is the centres of large cities while black
(transparent) is for remote areas. The magnitude/square arc-sec
scale is used for measuring the sky brightness. A 22 mag/sq arcsec
reading would be equivalent of 22 magnitude star in a 1 arcsec
area of the sky. The OMI is to be located in the darkest available
area in southern Ontario, a dark peninsula located near the small
town of Denbigh. This area is in the grey and rates 2 on the Bortle
scale with limiting magnitude of 7.1 to 7.5. The apparent sky
brightness is between 1% and 11% brighter than the natural background.
In addition light bubbles can be seen on the horizon. Ottawa is
the most prominent of these reaching a maximum height of 10 degrees
above the horizon. In addition light bubbles can be seen from
Smiths- Falls + Perth, Kingston, Toronto, Bancroft and Renfrew.
These are quite small reaching from 2 degrees to 5 degrees in
height.
Next: Light Bubbles
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