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Introducing myself

This presentation by Wim Schmidt delves into the variations in sky luminance, focusing on both natural and artificial light sources. With over a decade's experience as the chairman of the Dutch Light Pollution Group, Schmidt provides extensive data and insights on how different factors such as the sun, moon, and clouds influence sky brightness. It discusses the significance of standard measurements, the impact of geography and weather, and the stark contrasts in light pollution across various regions. Engage in understanding how we measure and interpret sky luminance and its implications for dark sky preservation.

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Introducing myself

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  1. Variations in sky luminance measurementsWim Schmidt Platform Lichthinder Sotto le StelleOsnabruckOktober 2011

  2. Introducing myself • Ten years chairman of the Dutch Light Pollution Group • Occupation: light pollution adviser: delivering data to governments: pictures, numbers and maps.

  3. Content • What are we measuring? • Variations in space • Variations in time

  4. What are we measuring? • Sun and moon and clouds • Stars • Milky way • Natural darkness • Artificial light Our interest: artificial light

  5. What are we measuring: sun and moon, clouds Astronight: • Altitude sun: < -18 degrees • Altitude moon < 0 degrees Clear sky: clouds give till 5 magnitudes more light

  6. What are we measuring: stars • A magnitude 22 sky gives light of 847 magnitude 0 stars. • All 6000 visible stars give light of 80 magnitude 0 stars. • Stars contribute less than 10% of the sky luminance • In direction of Milky way higher • In direction of horizon much lower • Natural sky: varies a little; difficult to determine

  7. What are we measuring: artificial light • At 5 locations 30 measurements in different nights: till 30 % variation; most around 10%. • Extinction correction • Geography and weather • Time of the night?

  8. What are we measuring: artificial light • Sky luminance dependent of extinction: higher extinction, higher sky luminance • A standard atmosphere (12 km horizontal sight and 0,3 magn extinction) • But still 6 till 20% differences.

  9. Geography and weather Groundmist: less light High layer, small distance: more light High layer, great distance: less light

  10. What are we measuring: Standard conditions • We need a standard about influence of moon and sun • We need a standard atmosphere • Always be some variance in measurements: weather conditions and local geography: do more measurements to get the variance at a location

  11. Variations in space • 2000 measurements sky luminance of the zenith • Minimum value: 0,27 mcd/m², around magn 21,8 • Maximum value 30 mcd/m², around magn 16.

  12. Variations in space • The Netherlands are not totally light polluted • Big differences between west and north • In the north: pristine conditions, comparable to the best places in Europe • Large difference between towns and countryside.

  13. Variations in space • Steep gradient on the edge of a greenhouse area: from 29 till 2 mcd/m² in 2 kilometre Gradient on the edge of town: From 8,5 till 2,5 mcd/m² in 7 kilometre Greenhouse area North east part of Amsterdam

  14. Variations in space Sky luminance - population relation of towns Is this real?

  15. Variations in time • Two years of measurements with SQM-LE and Austrian Lichtmeter Mark 2.3

  16. Variations in time • 5,5 magnitude variation • Increase darkness till 1 or 2 o’clock: less light? • Decrease darkness after 2 o’clock : inversion layer gets thicker?

  17. Variations in time • Maximum red dots: Increase of 0,22 magnitude in two years • Mean green dots: increase of 0,08 magnitude in two years • Explanation? Getting darker? Higher trees? Sensor ?

  18. Information Email: Wim Schmidt: wim.schmidt@sotto.nl Website: www.sotto.nl

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