In article ,
(Eric Chomko) writes:
My understanding is that when Jupiter and Saturn are near conjunction,
the barycenter between them and the sun is about 100K miles away from the
solar corona in the direction of the planets. I believe that Asimov
discussed this in his book, "Jupiter".

That's about 0.35 of a solar radius, which sounds about right. I
haven't done the calculation.

Also, don't we know about the existence of planets outside the solar
system due to the relationship between the barycenter of the star and its
apparent motion related to it?

Well, sort of. The thing that is actually measured is the radial
velocity of the star. If we imagined that the whole effect above was
due to Jupiter, the Sun would move 2.7 times its radius in about 6
years (half Jupiter's sidereal period). (The barycenter stays
"fixed," while the Sun moves from one side of it to the other.) For
a distant observer located in the orbital plane, the average velocity
seen would be 1.9E9 m/1.8E8 s = 10 m/s. (Of course the radial
velocity won't be constant; it will follow a sine wave in the case of
a single planet.) Measurement errors these days are of order 1 m/s
(Any experts want to correct me on this?), so in the simplest case,
Jupiter's effect on the Sun ought to be detectable by a distant
observer after monitoring for a dozen years.

There are, however, complications. On average, a distant observer
will not be exactly in the orbital plane, and Saturn, with its 29
year period, will make the motion more complex.

You might want to plug in all the numbers and do a little simulation.
Any spreadsheet program should suffice. Calculate the velocity for,
say, every tenth of a year for 100 years, and plot the results. If
you do this, you should check whether Uranus and Neptune will produce
a noticeable effect. (Once you have done one planet, adding in more
columns for more planets should be easy.)

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Steve Willner Phone 617-495-7123
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