Abhimanyu Chawla

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TWICE IN A LIFETIME Frequency of Venus Transit
Abhimanyu Chawla Department of Physics, Panjab
University, Chandigarh
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Frequency of Venus TransitsSynodic
PeriodDemonstration Activity
Contents
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Frequency of Venus Transits
Come in pairs that are eight years
apart Followed alternately by spans of 121 ½
years and 105 ½ years. Hence twice in a
lifetime! But why is it so rare?
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Synodic Period
Time required for a planet to move from a certain
position, with respect to the Sun, back to that
same position as seen from Earth.
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Synodic Period
For Earth 365 days ? 360 degrees Hence, in one
day ? 360/365 0.986 degrees For Venus 225
days ? 360 degrees Hence in one day ? 360/225
1.6 degrees
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Synodic Period
Each day Venus gains (1.6-0.986) degrees on
Earth (1.6-0.99) degrees in ? 1 day, So 360
degrees in ? 360/(1.6-0.986) 586 days 1.6
years This is the Synodic Period of Venus After
every 1.6 years, Venus comes in the same position
w.r.t the Sun, as seen from the Earth.
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Activity
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Two factors
Inclined Orbit
The orbit of Venus is tilted about 3.394 with
respect to the orbit of Earth
Orbital Speed
Time taken by Venus to complete a lap is not
exactly 8/13th the time by Earth, rather 7.997/13
? Inferior Conjunctions shift clockwise.
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