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Thread: Concening Europa's Eclipse Times?

  1. #1 Concening Europa's Eclipse Times? 
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    Question!

    If Europa orbits Jupiter every 85.2 hours that means that a Europan day is 42.6 hours (If I'm correct in understanding). I know It is tidally locked. But I realize that it must be eclipsed by Jupiter at some point in it's day and try as I might nor Google or Bing will grace me with the answers I desire. So I would be very grateful to know how long and how often Europa is eclipsed each Europan day.


    Any input will be greatly appreciated. Thanks Guys!


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  3. #2  
    Moderator Moderator Janus's Avatar
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    Europa is eclipsed between 2.5-2.88 hrs. Eclipses occur roughly every 85.27 hours.

    If Europa orbits Jupiter in 85.2 hrs then its "day" (sunrise to sunrise) is 85.27 hrs. And it is eclipsed once a "day".
    I gave a range for the eclipse times because Europa's orbit is inclined to the ecliptic. While the inclination is not enough for it to clear Jupiter's shadow completely, it does mean that width of the shadow is does pass through does differ from eclipse to eclipse.


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    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    flattened rat 甘肃人's Avatar
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    Wait a minute! Wouldn't a satellite's orbit around its planet be its year? Its day would be the body's rate of rotation.

    And maybe the reason the OP cannot find much information on Europa's eclipses, besides the downright arcanity of the topic, is that the eclipse would depend on the position of the observer. Okay, people on Earth are the observers, but can Europaean eclipses be observed without a powerful telescope?
    And what does the Lord require of you but to love justice, to be merciful and to walk humbly with Him?
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  5. #4  
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    Technically since Europa is locked tidally in much the same was as our moon one day is equivalent to one rotation around Jupiter.
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  6. #5  
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    And thank you Janus for the reply!
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  7. #6  
    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by 甘肃人 View Post
    Wait a minute! Wouldn't a satellite's orbit around its planet be its year? Its day would be the body's rate of rotation.

    And maybe the reason the OP cannot find much information on Europa's eclipses, besides the downright arcanity of the topic, is that the eclipse would depend on the position of the observer. Okay, people on Earth are the observers, but can Europaean eclipses be observed without a powerful telescope?
    A solar day (or Sol) is the time it takes for the sun to go from zenith to zenith. For Europa, since it is tidally locked to Jupiter and rotates in the same time as it takes to orbit Jupiter, its day works out to be equal to the time it takes Europa to orbit Jupiter with respect to the Sun. ( which is a tad bit longer than it takes to orbit with respect to the stars.)

    Eclipse duration is equal to the time it takes for Europa to pass through Jupiter's shadow. This can be worked out from the following.

    We know how far Europa is from Jupiter. We know Jupiter's diameter. From this we can work out how big Jupiter looks from Europa in terms of degrees. We know how long it takes the Sun to travel from Zenith to Zenith as seen from Jupiter (85.27 hrs) , which gives us the angular speed(degree/sec) of the Sun across Europa's sky. We now just work out how long it would take the Sun to cross the disk of Jupiter at this speed as seen from Europa and we have a good estimate of the eclipse duration.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  8. #7  
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by 甘肃人 View Post
    Okay, people on Earth are the observers, but can Europaean eclipses be observed without a powerful telescope?
    That would require an anthropomorphic, rather than scientific, definition of eclipse.
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