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At which distance can you see Saturn's ring with a naked eye?

  1. May 19, 2013 #1
    At which distance can you see Saturn's ring with a naked eye? I guess you would not be able to see it from Mars?
     
  2. jcsd
  3. May 19, 2013 #2

    Chronos

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    Roughly 300,000,000 kilometers, or about 22% of its current distance. The rings of Saturn would not always be discernable even if it were in the orbit occupied by Mars.
     
  4. May 20, 2013 #3
    i'm assuming that this is b/c 1) when the Sun is more or less directly between Mars and Earth, Mars is much farther than 300,000,000km away from us, and 2) even if Saturn were 300,000,000km away or less, the visibility of its rings would still depend on the angle of inclination of the ring plane with respect to the line of sight of the ground observer?
     
  5. May 24, 2013 #4
    Chronos, how did you come about that number? Just curious, thanks.
     
  6. May 24, 2013 #5

    Chronos

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    It takes about a 25x telescope to resolve the rings of Saturn. For Saturn to appear 25 time larger to the unaided eye, it must be 4.67 times closer (inverse square law - 2^n = 25; n = 4.67). The average distance to Saturn is about 1.4 billion kilometers (1.2 minimum, 1.67 maximum). 1.4 billion / 4.67 is about 300 million.
     
  7. May 24, 2013 #6
    Completely wrong!

    You are taking logarithm and calling it square root. And you should not have even root in the first place, because telescope magnification is quoted as linear.

    Saturn with rings is about 46 arc seconds wide at opposition closest approach to Earth. So at 40x magnification, or approaching to 0.25 AU, Saturn´s rings will span the width of full Moon.

    But you can see many details on Moon. How much do you need to magnify Saturn to detect that it is not a point?
     
  8. May 24, 2013 #7

    mfb

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    The angular resolution of the eye is somewhere between 1 and 4 arcminutes. If Saturn's rings appear under an angle of 4 arc minutes, it could be possible to see some structure (basically a deviation from a round object). To get this, we have to be 6 times closer to Saturn, which corresponds to a distance of ~1.3 AU or ~200 million km.
     
  9. May 24, 2013 #8
    A magnification of x2 - x4 should do. But the hard question is what "see Saturn's rings" translates into. At the magnification Chronos suggested (x25) Saturn would be quite small but most people should be able to clearly see the rings. If the nights (I live at 60 deg north) wasn't already much to bright and Saturn so close to the horizon I'd be tempted to go out and try this with one of my telescopes and my 7x35mm, 10x50mm and 15x70mm binoculars.

    ETA: I watched Saturn in binos before but it has been several years since last time so the memory is not fresh.
     
    Last edited: May 24, 2013
  10. May 24, 2013 #9

    Chronos

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    Under the square root law, the coversion factor is n^2, not 2^n (I plead dyslexia). At a distance of 1.4 billion km, Saturn would need to be at a distance of 280 million km, not 300 million km to magnify it by 25x.
     
  11. May 24, 2013 #10
    I use a cheap pair of 10x50's in an area with a Bortle scale 6ish sky and it appears not circular (certainly irregular). If I didn't know it was Saturn I'm not sure what I would infer. (saturn is around a 40 degree altitude at my latitude during local time 22:00)
     
  12. May 24, 2013 #11
    You missed the important part of his message, resolution is inverse linear with distance not inverse square distance. To get 25 times more resolution you need to be 25 times closer or 56 million km using your values.
     
    Last edited: May 24, 2013
  13. May 24, 2013 #12
    I disregarded my previous statement and utilized a gap in the clouds to set up my 15x70mm binos on a tripod. Bad seeing due to the low altitude at my location but even if you didn't know about the rings Saturn would definitively look very odd compared to other planet (the rings where very noticeable with x15 at the current distance of 8,9AU/1,33 billion km).
     
  14. May 24, 2013 #13

    russ_watters

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    glappkaeft is right, Chronos. "Magnification" is a measure of the linear increase in size, not the area increase in size. If you bring an object half as far away, you increase its apparent diameter by a factor of two.

    http://www.rocketmime.com/astronomy/Telescope/Magnification.html
     
  15. May 24, 2013 #14
    How about this, for resolving the actual gap with the naked eye:

    The rings start about 7000 km above the visual atmosphere. To resolve this separation with an eyeball that has resolving power of 1' (=60"), the angular separation can't exceed 60":

    angular separation (arcseconds) = 206265 Separation/Distance

    So,

    60 = 206265 * 7000 /D

    or

    D = 206265 * 7000 / 60 ~ 24 million km (~0.16 AU)
     
  16. May 24, 2013 #15

    Chronos

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    Agreed. Saturn, at 280,000,000 miles would have 25x more area, not 25x more angular diameter. Too much lawnmower exhaust :redface:
     
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