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Introducing myself

Variations in sky luminance measurements Wim Schmidt Platform Lichthinder Sotto le Stelle Osnabruck Oktober 2011. Introducing myself. Ten years chairman of the Dutch L ight P ollution Group Occupation: light pollution adviser: delivering data to governments: pictures, numbers and maps.

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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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