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The twice-in-a-lifetime event: Transit of Venus 2012. http ://www.skyandtelescope.com/observing/objects/daylightphenomena/3308756.html. Venus takes 224.7 days to orbit the su n. Earth takes 365.24 days (1 calendar year) Earth, sun and Venus are realigned every 583.92 days, a synodic year
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The twice-in-a-lifetime event:Transit of Venus 2012 • http://www.skyandtelescope.com/observing/objects/daylightphenomena/3308756.html
Venus takes 224.7 days to orbit the sun • Earth takes 365.24 days (1 calendar year) • Earth, sun and Venus are realigned every 583.92 days, a synodic year • 5 Venus synodic years @ 8 Earth calendar years
Why isn’t there a transit every inferior conjunction? • For a transit, Earth, Venus and the sun must line up almost EXACTLY in all 3 dimensions • Venus’ orbit plane is tipped with respect to Earth’s – the planes intersect at 2 points (Earth’s location in June & December)
8 years from now? Graphics and reality checks from Royal Astronomical Society of New Zealand’s web page on Venus transit
Why has this been an important event in astronomical history?
A means to measure the scale length of the solar system Copernicus supplied correct scale model of the solar system; he did not know that the “scale unit” (the AU, or Astronomical Unit) was about 150,000,000 km
If Earth is 1 AU from the sun, • Venus’s average distance from sun is 0.62 AU • At inferior conjunction, Venus is 0.28 AU from Earth