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Thread: suppose you go to mars for a weekend..

  1. #1 suppose you go to mars for a weekend.. 
    Forum Freshman noob's Avatar
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    let us ignore all facts and imagine you really could go there now.

    comparing with view of moon from earth, how large would phobos and deimos be on sky?
    could you see earth in night?
    would jupiter be much larger?
    how much would sun be less visible in day?

    give me anything....

    cheers 8)


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  3. #2 Re: suppose you go to mars for a weekend.. 
    Moderator Moderator TheBiologista's Avatar
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    Quote Originally Posted by noob
    let us ignore all facts and imagine you really could go there now.

    comparing with view of moon from earth, how large would phobos and deimos be on sky?
    could you see earth in night?
    would jupiter be much larger?
    how much would sun be less visible in day?

    give me anything....

    cheers 8)
    I'm no expert, so correct me if I'm off on this. Phobos and Deimos will look small- like very bright stars. They're just very small moons, nothing like ours in size. Earth will be visible sometimes depending on where you are, just as Mars is sometimes visible from Earth. It'll also look like a rather bright star. Jupiter will be larger than seen from Earth sometimes (when Mars and Jupiter are close in orbits) and smaller sometimes (the larger radius of Mars' orbit will mean it can get further from Jupiter than Earth can. The sun will look much smaller, I think there's some decent pictures of the Sun, Earth and some of Mars' moons from the surface. They were taken by the Spirit and Opportunity rovers.


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  4. #3  
    Moderator Moderator Dishmaster's Avatar
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    Those quantities can be easily calculated, if the basic properties (distances and sizes) are known. You need values for the Sun, Earth, Jupiter, Mars, Phobos, and Deimos. Then you can use simple trigonometric relations like , where is the radius of the body, whose apparent angular radius should be determined, and is its distance from the point of view. Note that the distance between the point of view to the observed body is not the distance between the two bodies. Example: In order to calculate the apparent diameter of Phobos when viewed from the surface of Mars, the distance is reduced by the Mars radius. From this, one can derive:

    Apparent diameter of Sun from Mars: 21 arcminutes
    Apparent diameter of Phobos from Mars: 11.4 arcminutes
    Apparent diameter of Deimos from Mars: 2.6 arcminutes
    Apparent diameter of Jupiter from Mars: approx. 29 - 52 arcseconds (largest and smallest distance)
    Apparent diameter of Jupiter from Earth: approx. 31 - 46 arcseconds (largest and smallest distance)

    Here is a short movie of a solar eclipse caused by Phobos as observed from Mars by the probe Opportunity.
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  5. #4  
    WYSIWYG Moderator marnixR's Avatar
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    what's the time scale of the transit ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  6. #5  
    Moderator Moderator Dishmaster's Avatar
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    Quote Originally Posted by marnixR
    what's the time scale of the transit ?
    According to this article, it takes about 20 to 30 seconds. More examples of transits seen from Mars can be found here.
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  7. #6  
    Moderator Moderator TheBiologista's Avatar
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    Quote Originally Posted by Dishmaster
    Those quantities can be easily calculated, if the basic properties (distances and sizes) are known. You need values for the Sun, Earth, Jupiter, Mars, Phobos, and Deimos. Then you can use simple trigonometric relations like , where is the radius of the body, whose apparent angular radius should be determined, and is its distance from the point of view. Note that the distance between the point of view to the observed body is not the distance between the two bodies. Example: In order to calculate the apparent diameter of Phobos when viewed from the surface of Mars, the distance is reduced by the Mars radius. From this, one can derive:

    Apparent diameter of Sun from Mars: 21 arcminutes
    Apparent diameter of Phobos from Mars: 11.4 arcminutes
    Apparent diameter of Deimos from Mars: 2.6 arcminutes
    Apparent diameter of Jupiter from Mars: approx. 29 - 52 arcseconds (largest and smallest distance)
    Apparent diameter of Jupiter from Earth: approx. 31 - 46 arcseconds (largest and smallest distance)

    Here is a short movie of a solar eclipse caused by Phobos as observed from Mars by the probe Opportunity.
    Good post and a great picture too!

    Amazing to think that Opportunity's sister probe Spirit today (Jan 4) completed her 5th year of activity on the surface of Mars. What a trooper!
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  8. #7  
    Moderator Moderator Janus's Avatar
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    Just for comparison, here's what what Phobos would look like from the surface of Mars as compared to what the Moon looks like from Earth.

    For a good idea of what you would see, print this image out so that it has a width of 1.66 inches, tape it to the wall and then step back 9 1/2 feet from the wall.

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


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  9. #8  
    Moderator Moderator Dishmaster's Avatar
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    Very nice! :-D Thanks Janus!
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