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The Sun as seen from 120 AU.

  1. Jun 26, 2012 #1
    Hi all

    Currently, Voyager 1 is about 120 AU from the Sun. I wonder how big (or small) and bright would the Sun be seen from aboard this spacecraft. What approximate magnitude?.

    Thanks in advance.
  2. jcsd
  3. Jun 26, 2012 #2
    Here, thanks to Caltech, is an artist's conception of the Sun from the vicinity of Sedna at 8 billion miles' (about 86 AU) distance:

  4. Jun 26, 2012 #3


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    It's still very bright, even at 120 au, at about magnitude -16.3 [the full moon from earth is about -12.7. So you would easily be able to read a newspaper. It would, however, be a virtual point source at that distance.
  5. Jun 27, 2012 #4
    BadBrain and Chronos

    Thanks a lot for your replies. That of being able to read a newspaper is a very interesting detail.

    thanks again.
  6. Jun 27, 2012 #5
    On a related topic, I heard that voyager was still accelerating, why? What causes it to accelerate further?
  7. Jun 27, 2012 #6
    The angular size θ of the Sun's disk is given by the formula:
    \sin \left( \frac{\theta}{2} \right) = \frac{R_S}{d}
    where RS is the radius of the Sun, and d is the distance from it.

    Because the distance is much larger than the Sun's radius, the sine is very small. Therefore, to a sufficient precision we may substitute:
    \sin \left( \frac{\theta}{2} \right) \approx \frac{\theta}{2}
    provided that we measure the angle in radians. Nevertheless, we see that:
    \theta \approx \frac{2 R_S}{d} \propto \frac{1}{d}
    the angular size is approximately inversely proportional to the distance. At 1 A.U. (the Earth), the angular size of the Sun is about 31' (arc minutes). Therefore, at 120 A.U. it is:
    \theta = \frac{31 '}{120} \times \frac{60 ''}{1 '} = 15.5 ''
    that is about 15 arc seconds.
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