Sperm Whales, Candles and Planet Venus An investigation of John Isaac Plummer's 1876 estimation of t

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Sperm Whales, Candles and Planet VenusAn
investigation of John Isaac Plummer's 1876
estimation of the brightness of Venus

• James Appleton

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John Isaac Plummer (1845 1925)In a
photograph believed to have been taken around
1900, while he worked at Hong Kong Observatory
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Phases of Venus
Superior conjunction
Inferior conjunction
Observer on the Earth looking towards Venus
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Zoellner Photometer, 1860
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The Inverse Square Law of Illumination

• For a point light source (like a distant star)
  the flux of light per unit area varies as the
  inverse square of the distance

Area of spherical shell at distance r is 4pr2
r
Point light source
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Rumford Photometer
Vary distance, C, to reference light source until
shadows are of equal intensity. 1/C2 is then a
measure of the brightness of X in terms of the
brightness of the reference light source.
X light source of intensity to be measured
Reference light source
C
Metal rod
White screen
Shadow
Shadow
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Plummers Photometer Modified Rumford
Venus
C typically 100m
Candle inside lantern inside black box
Metal rod, 1.8mm diameter
2.7m
2.7m
Paper screen
Paper screen
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The Reference Light Source
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Observations of Venus, 1876
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Atmospheric Extinction
Object at zenith light has a relatively short
path through atmosphere
Object near horizon light has a relatively long
path through atmosphere
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Observations of Venus, 1876
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Data Analysis

• Inspect discard bad data
• Square values C and adjust for atmospheric
  extinction
• Adjust for planetary geometry
• Plot brightness of Venus against phase

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Inspect Discard Bad Data
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Remaining Observations
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Square C and Adjust for Atmospheric Extinction
E Atmospheric extinction
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Adjust for Planetary Geometry
G Planetary Geometry
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Brightness vs Phase
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Brightness vs Phase
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Brightness vs Phase
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Now lets look at some practical aspects
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And the conclusions are
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Skyglow Around Jupiter
27 Sep 2008 2120 UT Jupiter mag -2.3
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The Photometer in Use
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Looking Down the Tube
Jupiter mag -2.6
24 Aug 2008 2103 UT
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Atmospheric Extinction Factors
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Brightness vs Phase