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Old July 5th 03, 08:03 AM
Odysseus
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Default Solar System Movement in the Galaxy

"J. M." wrote:

I knew the Earth and the other planets moved around the sun in orbit.
What I didn't know was that the Solar System is also in orbit around
something. Along with everything else in the galaxy, it is in orbit
around the center of the galaxy. Am I correct?

Yes.

The Voyager spacecraft is not in orbit around the sun. From what I
understand it is moving away from the sun at a constant speed in one
direction. But for some reason, it moves with the sun around the
galaxy? Why is that?

Like everything else in the galaxy, it continues to be affected by
the combined gravitational attraction of the objects in it. Since it
started out with more or less the same velocity as the sun, and isn't
travelling terribly fast -- comparatively speaking -- its orbit
around the galactic centre will remain similar to the sun's.

This goes on and on and one day Voyager will leave the solar system.
From what I read, before leaving the solar system, the spacecraft will
go through something called the heliopause. Is that when the sun will
stop having effect on Voyager? Right now, Voyager, with the solar
system, is in orbit around the galaxy center. When Voyager leaves the
Solar System (goes through the heliopause), will the Solar System
continue its orbit around the galaxy center without Voyager or will
Voyager continue to move around the galaxy center with us forever?

The heliopause is the boundary around the 'bubble' created by the
solar wind, so once Voyager has passed outside it will truly be in
interstellar space. But the sun's gravity will continue to influence
it slightly, gradually tapering off as the probe moves further away
but with no 'cutoff point'.

See http://antwrp.gsfc.nasa.gov/apod/ap020624.html.

If Voyager stops orbiting around the galaxy center, does that mean
that at that point, the distance between Earth and Voyager will start
growing even faster, because we would be going in one direction and
Voyager in another?


We are already, but only to a very slight extent on the scale of
stellar motions. Barring a 'near miss' with another body that might
perturb the galactic orbits, Voyager will be travelling more or less
'alongside' the solar system for millions of years.

--Odysseus