Leeds Astronomical Society LAS Meetings Observing Membership

 

 

Light Pollution in Leeds

 

 


It's a deprivation for us all to never see a dark night sky. It's not just astronomers who would miss it just as it's not just ornithologists who would miss songbirds if they disappeared from our gardens.

Lord Rees of Ludlow, Astronomer Royal.

Leeds is a typical example of a UK city, where wasted light spills out for many miles into the countryside. Lights from vacant offices, shops & car-parks are needlessly left on at all hours of the night; the majority of our street-lights have no controls; and there is no environmental 'plan' for permitted lighting levels. Statutory regulations are also inadequate; local planning considerations around lighting are perfunctory at best; and in shops & DIY stores, exterior lighting products are poorly designed, too bright or inefficient. It's not surprising then, that in CPRE's annual Star-Count, Leeds falls under the 'severe light pollution' category.

It hasn't always been this way - the problem of light pollution has been gradually creeping up on us since the 1950s. Over time lighting has got cheaper, brighter and much more prolific. Up until the 1950s practically everybody would have been able to see our galactic home - the Milky Way. Today it's thought that about 85% of the UK population have never seen it & nobody living in the Leeds area stands a chance of seeing it from the back gardens.

For amateur astronomers this is a nuisance, but there are also arguably more important environmental impacts of Artificial Light At Night (ALAN), particularly for nocturnal wildlife, including insects which have suffered sharp population declines in recent decades.

Today's Lighting technology has improved to the point where there is now the opportunity to provide adequate lighting where and when it is needed, but in an efficient and environmentally friendly manner. All that's needed is the willingness to do so.

 


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Bortle

The Bortle scale is a nine-level numeric classification which indicates the quality of the night sky based on the visible objects. As the Bortle number increases, the sky quality deteriorates, with Class 9 being an 'Inner-City' sky and Class 1 a perfect dark sky site.

The scale was developed by John E. Bortle and first published in Sky & Telescope magazine in 2001.

ClassTitleNELMDescription
9Inner-City sky4.0
  • The entire sky is brightly lit even at the zenith.
  • Many stars are invisible and only bright constellations are & planets discernable.
8City sky4.1 - 4.5
  • The sky is light grey making newspaper headlines readable
  • Some of the stars in familiar constellations are hard to detect or are absent
  • Only bright Messier objects visible detectable with telescopes
7Suburban/Urban transition4.6 - 5.0
  • Entire sky has vague greyish white hue
  • Strong light sources evident in all directions
  • The Milky Way is invisible
  • Clouds are brilliantly lit
  • Even in modest telescopes bright Messier objects are diminshed
6Bright Suburban sky5.1 - 5.5
  • The sky within 35° of the horizon glows grey-ish white
  • Clouds anywhere in the sky appear fairly bright
  • Even high clouds (cirrus) appear brighter than the sky background
  • Surroundings are easily visible
5Suburban sky5.6 - 6.0
  • Light pollution is visible in most, if not all, directions
  • Clouds are noticeably brighter than the sky
  • The Milky Way is very weak or invisible near the horizon, and looks washed out overhead
4Rural/Suburban transition6.1 - 6.5
  • Surroundings are clearly visible, even at a distance
  • Clouds are illuminated in the directions of the light sources, but appear dark overhead
  • Light pollution domes visible in several directions
  • The Milky Way well can be seen away from the horizon, but lacks detail
3Rural sky6.6 - 7.0
  • Nearer surroundings are vaguely visible
  • Some light pollution evident at the horizon
  • The summer Milky Way still appears complex
  • Clouds are illuminated near the horizon, dark overhead
  • M31 is visible with the naked eye
2Typical truly dark sky site7.1 - 7.5
  • Surroundings are barely visible silhouetted against the sky
  • Clouds are only visible as dark holes against the sky
  • The summer Milky Way is highly structured
  • Airglow may be weakly visible near horizon
  • M33 is visible in averted vision with the naked eye
1Excellent dark sky site7.6 - 8.0
  • Many constellations, particularly fainter ones, are barely recognizable amid the large number of stars
  • M33 is visible in direct vision with the naked eye
  • The zodiacal band is visible
  • Airglow is readily visible
  • Venus and Jupiter affect dark adaptation

In the UK the best skies come into the Bortle Class 3.

 

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