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When I read JPL's mission status for Voyager 1 and Voyager 2 the distance between Earth and Voyager 1 is decreasing.

Is it right?

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    $\begingroup$ what-if.xkcd.com/38 $\endgroup$ Feb 6, 2018 at 13:41
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    $\begingroup$ The question is backwards -- it's "why is the Earth approaching Voyager 1"? $\endgroup$ Feb 6, 2018 at 20:17
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    $\begingroup$ @JohnDvorak xkcd.com/1189 $\endgroup$
    – jpmc26
    Feb 7, 2018 at 0:28

1 Answer 1

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Voyager $1$ is headed away from the Sun at around $17$ km per second at an angle to the ecliptic of around $35$º.

The orbital velocity of the Earth is $29.8$ km per second, and multiplying by $\cos 35$º to get the component of the velocity in Voyager's direction gives a shade over $24$ km per second.

So at the point in its orbit where Earth is moving closest to the direction of Voyager's travel we are actually catching up with it at around $24 - 17 = 7$ km per second. Conversely at the point in Earth's orbit where it is moving opposite to Voyager it is moving away from us at $24 + 17 = 41$ km per second.

Voyager relative speed

(not to scale!)

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    $\begingroup$ And here I always thought that the Earth was larger than the Sun, and Voyager was larger than both. Thanks for clearing things up by pointing out that the diagram is not to scale. ;-) $\endgroup$ Feb 6, 2018 at 14:29
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    $\begingroup$ I'm 72% certain these diagrams are scaled correctly $\endgroup$ Feb 6, 2018 at 16:59
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    $\begingroup$ (percentage not to scale) $\endgroup$ Feb 6, 2018 at 20:46
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    $\begingroup$ I'm sure the earth is blue, not green. That's what they tell us at school, meh. $\endgroup$
    – image357
    Feb 6, 2018 at 22:20
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    $\begingroup$ At least you got it right by keeping the earth flat. $\endgroup$
    – Jon P
    Feb 7, 2018 at 0:09

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