What does the Bortle scale refer to?
spectrum of the stars
types of nebulae
brightness of the night sky
size of the planets
The Bortle scale is a nine-level numeric scale that measures the night sky's brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution. It was created by John E. Bortle in 2001.
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Answers by country
spectrum of the stars
types of nebulae
brightness of the night sky
size of the planets
answers
 Switzerland
Switzerland20
 France
France16
 the United States
the United States157
 South Africa
South Africa13
 Australia
Australia39
 Austria
Austria58
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the Philippines24
 Estonia
Estonia11
 Pakistan
Pakistan17
 Germany
Germany329
 Canada
Canada22
 the United Kingdom
the United Kingdom102
 India
India295
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Poland4740
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Republic of Ireland20
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the Netherlands10