Bortle scale
The Bortle scale indicates the extent of light pollution at an astronomical observation site.
Classification
In contrast to seeing scales , the degree of light pollution is mainly determined without optical aids. In addition to some simple methods of classification, such as counting stars in a certain region of the sky, there are also recognized scales. The most common is the Bortle scale published in February 2001 by John E. Bortle . They are divided into nine classes:
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Class 1 : extremely dark (desert) - limit size 8.0 to 7.6 like
zodiacal light , zodiacal band and counter-reflection noticeable. Airglow directly visible. The Milky Way in the constellations Sagittarius / Scorpio casts shadows. The galaxy M33 is a conspicuous object with direct vision to the naked eye. Jupiter and Venus hinder dark adaptation. Instruments and people cannot be recognized against a dark background. -
Class 2 : very dark (mountains) - limit size 7.5 to 7.1 likes
zodiacal light bright and color yellowish. Airglow faintly visible near the horizon. Summer Milky Way heavily structured. M33 easily recognizable with the naked eye and direct vision. Clouds in the night sky only appear indirectly as dark holes in front of the starry sky. Telescope only vaguely recognizable. -
Class 3 : Land - limit size 7.0 to 6.6,
zodiacal light is still recognizable in spring and autumn. Milky Way clearly differentiated. M33 easily recognizable with the naked eye and with averted vision. Horizon already polluted with light. Observation instruments clearly recognizable. -
Class 4 : transition country / suburb - limit size 6.5 to 6.1 likes
to see zodiacal light only partially. Milky Way clear, but partially already structureless. M33 hardly visible with averted vision either. Significant light pollution near the horizon. Clouds over settlements clearly brightened. Observation instruments very clearly recognizable. -
Class 5 : suburbs - limit size 6.0 to 5.6 likes
zodiacal light only recognizable on the best nights in spring or autumn. Milky Way hardly recognizable near the horizon, structureless at the zenith. Light pollution in all directions. Clouds also clearly brightened over the observation point, sometimes brighter than the sky. Observation instruments easily recognizable even without red light. -
Class 6 : bright suburbs - limit size 5.5 to 5.1 likes
no zodiacal light. Milky Way only at the zenith, M31 can barely be seen with averted vision . Sky up to 35 degrees gray / white. Clouds brightly lit. -
Class 7 : Transition suburb / city - limit size 5.0 to 4.6 likes the
whole night sky gray / white. Milky Way invisible. Even high clouds are brightly lit. -
Class 8 : City - limit size 4.5 to 4.1 likes
sky white / orange. Constellations with large gaps. Newspaper headlines easy to read. -
Class 9 : Inner city - limit size 4.0 mag and brighter The
entire night sky is brightly lit up to the zenith. Many stars in the constellations disappeared. Gaps in the sky completely free of stars. M45 the last recognizable Messier object.
Classes 1 and 2 no longer occur in Central Europe .
See also
Individual evidence
- ↑ Stefan Oldenburg: Deep Sky Objects visually. Part 2: Planning the observation night properly . In: Stars and Space . 12/2013, p. 89.