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Conjunction of Venus and Sun a rare event

  1. Apr 25, 2004 #1

    Kerrie

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    I won't get to see this rare event in my part of the U.S. :frown: However, I still wanted to share with you all this conjunction of Venus and the Sun June 8th, 2004.

    Venus Conjunction
     
  2. jcsd
  3. Apr 25, 2004 #2

    enigma

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    I'm confused what exactly is going on here...

    Venus is passing through the center of the Sun as viewed from Earth?

    Since we're near the spring equinox, I'd guess that means that Venus is near its node as well... from the pictures on that website, it looks like the descending node.
     
  4. Apr 26, 2004 #3

    Janus

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    A transit is any time Venus crosses any part of the body of the Sun as seen from Earth ( It doesn't have to pass through the center), And yes, it only occurs when Venus is near its node during a conjunction.)

    I was also slightly confused by the title of this thread since it appeared to imply that a conjunction with Venus was a rare event. A conjunction occurs when ever Venus and the Earth pass each other in their orbits; this occurs fairly regularly. Transits are much rarer.
     
  5. Apr 26, 2004 #4

    Kerrie

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    Sorry Janus, I used "conjunction" then as a wrong term? But yes, the transit of Venus passing directly in front of the sun is a rare event...the last time it happened was in 1882, and the even more weird thing about this is Venus is again expected to have a transit in 2004.
     
  6. Apr 26, 2004 #5

    selfAdjoint

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    I believe transits of Venus occur in pairs. At least I know there was a pair of them in the 1760s, which was the occasion of heroic expoditions to observe them. At that time they were the only way to determine the actual size of the solar system.
     
  7. Apr 26, 2004 #6

    Hurkyl

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    What does this mean in terms of someone wanting to observe the event?
     
  8. Apr 27, 2004 #7
  9. Apr 27, 2004 #8

    marcus

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    here's a webpage with some original drawings from the James Cook
    expedition to observe the transit of 1769. Cook's team observed the transit from Tahiti-----the page has some quotes from Cook's account to the Royal Socieity and some sketches of the temporary observatory they set up in Tahiti and their instruments.

    http://www.jcu.edu.au/school/mathphys/astronomy/jamescook2.shtml

    apparently it was Edmund Halley (of comet fame) who proposed, in 1716, that timing a transit of venus could serve to determine the AU. another page I happened to see said:

    "Edmund Halley, in 1716, suggested that the distance from the Sun to the Earth could be calculated by timing the transit of Venus across the face of the Sun. "
     
    Last edited: Apr 27, 2004
  10. Apr 27, 2004 #9

    selfAdjoint

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    The Jesuits also made expeditions, I think they went to the Pacific coast of North America, to the California missions run by the Fransiscans. There was no love lost. Apparently the track of the transit went from the South Pacific up across California and north into Canada, somewhere around the west end of Lake Superior. There was a book about all this, called The Transit of Venus and I'm posting from dim memories of reading it.
     
  11. Apr 27, 2004 #10

    marcus

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    do you happen to recall how (according to Halley's suggestion apparently) they were to calculate the AU from timing transit?

    To simplify let's assume the transit is across center of sun's disk so it describes a solar diameter

    I think that by measuring angular size of sun's disk they could tell that
    one AU is around 107 times the solar diameter, or 108 (we dont have to be accurate I just want to see in a rough way how they'd calculate)

    So the transit takes some time (like 8 hours?) that they measure.

    How would they calculate the AU from that?

    I suppose they could observe the angular size of Venus at the same time (it would be at a maximum I suppose) and i wonder if that information was also used in some way in the calculation of the AU.

    Maybe its so obvious to most people that the derivation doesnt even need to be explained but I dont immediately see it.
     
  12. Jun 8, 2004 #11

    Kerrie

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    even google recognized this event :P
     
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