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Sk B i ht M t ithSky Brightness Measurements with a Digital Camera:Digital Camera:

The Effect of a Small Nearby Village (Großmugl) on Night Sky Brightness

Georg ZottiGeorg Zotti

Wiener Arbeitsgemeinschaft für Astronomie

& Österreichischer Astronomischer Verein

Outline

Sky Luminance and Stellar VisibilityHi h D i R Ph t hHigh Dynamic Range PhotographyEvaluation of HDR imagesEvaluation of HDR imagesUrban vs Rural Night SkyUrban vs. Rural Night SkyGroßmugl Experiment,Großmugl Experiment, Astronomy Day 2008

Georg Zotti 1

Sky Luminance and Stellar Visibility

Human VisionHuman Vision

Full Moon SunsetFull Moon Sunset

Instrument VisionGeorg Zotti 2

Instrument Vision[after Weaver 1947, Garstang 1986, Cinzano 1997]

High Dynamic Range Photography

Combination of several exposuresCalibration with Luminance Meter

Luminance MapPh t hiPhotographic Measurement System

Georg Zotti 3

Our SystemCamera: Digital SLR

All Sky Fisheye only with Full Size Chip DSLRsAll-Sky Fisheye only with Full-Size Chip DSLRs RAW image format!

F S ftFree Software: Dcraw for RAW image processinghttp://cybercom.net/~dcoffin/dcraw/PFS Tools for HDR processing p ghttp://www.mpi-inf.mpg.de/resources/pfstools/

Extensible via GNU OctaveExtensible via GNU OctaveCalibration:

PFS Tools from EXIF data (approximative)PFS Tools, from EXIF data (approximative)Minolta LS-110 for daylight range

Georg Zotti 4

Sky Quality Meter for night sky measurements

Evaluation of Zenith Luminance

Series of HDR photos Averaged zenith area

TonemappedHDR images

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HDR images

Evaluation of Zenith Luminance

Sun alt

cd/m²alt.

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Evaluation of Zenith Luminance

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Results: Surburb SkyFull illumination Reduced illumination

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Results: Surburb SkyFull illumination Reduced illumination

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Results: City Border (average)Full illumination Reduced illumination

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Results: City Border (good night)Full illumination Reduced illumination

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Results: City Border / 20km from Viennamag5.5 Großmugl near Vienna, mag6

Vienna

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Results: 20km from Vienna / UnpollutedGroßmugl near Vienna, mag6.2 Pristine Sky (Mongolia) mag6.3

Vienna

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Results: 20km from Vienna / UnpollutedGroßmugl near Vienna, mag6.2 Pristine Sky (Mongolia) mag6.3

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A Rare View: Dark Clouds at Night!

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Astronomy Day, 2008-05-10, Großmugl

2 illuminatedroads

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Astronomy Day, 2008-05-10, Großmugl

2 illuminatedBLACKroads

1 illuminatedroadroad

Georg Zotti 17

Astronomy Day, 2008-05-10, Großmugl

2 illuminatedBLACKroads

1 illuminatedroad

BLACKroad

Lights off

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Astronomy Day, 2008-05-10, Großmugl

Lights offGroßmugl

ViGeorg Zotti 19

Vienna

Astronomy Day, 2008-05-10, Großmugl

Lights offBLACKGroßmugl

1 illuminatedroadroad, 10 minutesafter power-on

ViGeorg Zotti 20

Vienna

Astronomy Day, 2008-05-10, Großmugl

Lights offBLACKGroßmugl

1 illuminatedroad

BLACKroad, 10 minutesafter power-on

Back to „normal“

ViGeorg Zotti 21

Vienna

Astronomy Day, 2008-05-10, Großmugl

Lights offBLACKGroßmugl

1 illuminatedroad

BLACKroad, 10 minutesafter power-on

Back to „normal“

ViGeorg Zotti 22

Vienna

Astronomy Day, 2008-05-10, Großmugl

Lights offGroßmugl

ViGeorg Zotti 23

Vienna

Astronomy Day, 2008-05-10, Großmugl

Lights offBLACKGroßmugl

Back to „normal“

ViGeorg Zotti 24

Vienna

Open Questions

Calibration:Reference photometer not sensitive enoughfor dark scenefor dark sceneSQM sensitivity non-photopicSQM (older model) field of view difficult

Wh t i th b t“ k b i ht it?What is the „best“ sky brightness unit?cd/m²cd/mmag/arcsec²Limiting visual magnitude

Can we agree on a common colour scale?Can we agree on a common colour scale?Georg Zotti 25

Street Luminaires at Kuffner Observatory

Last SundayLast Sunday

MoonMoon

Street lamp

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Street Luminaires at Kuffner Observatory

Last SundayLast Sunday

Moon TuesdayMoon

Street lamp

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Street Luminaires at Kuffner Observatory

Last SundayLast Sunday

Moon TuesdayMoon

Street lamp

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Street Luminaires at Kuffner Observatory

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Conclusions

All-Sky Luminance Measurement SystemCalibrated HDR Imaging SystemSimple extensions to PFS ToolsSimple extensions to PFS ToolsFalse-Colour Plots

For “technical” astronomers: mag/arcsec²For visual star watching: limiting visual magnitudesg g gPFS base units: cd/m²

Light Pollution in rural areas ruins esp horizon skyLight Pollution in rural areas ruins esp. horizon skyEffect of road light reduction clearly visible

Thank you for Your AttentionGeorg Zotti 30

Thank you for Your AttentionGeorg Zotti <gzotti@cg.tuwien.ac.at>