# Thread: The solar system's motion thru space

1. Order of Kilopi
Join Date
Dec 2004
Posts
11,219
I'm basically saying what Hornblower said. I wrote
all below except the final sentence before he posted.

Originally Posted by grapes
The shuttle always did go around me, and you,
still does. But that is different than saying the
shuttle orbits me, or you. No?
Yes, but the Shuttle used to orbit us, not just go
around us.

Originally Posted by grapes
What is meant by "truly" there?
Same as you meant by "really" when you said
"... it doesn't really orbit the barycenter ..."
When I wrote "really, truly" I had in mind little kids
who are struggling to differentiate between fiction
and fact. One in particular who seemed not to know
what information to trust.

Originally Posted by grapes
Why wouldn't you say the Earth truly orbits the
sun-jupiter barycenter too?
Because I'm not sure what the correct statement is.

I know that one focus of Earth's elliptical orbit is
approximately at the center of the Sun. I also know
that all the other matter in the Universe affects that
orbit, and thus the location of the focus. Obviously
all the matter inside Earth's orbit acts to increase
Earth's centrepital acceleration. The sum is the
barycenter of the "inner" part of the Solar System.

But all the matter outside Earth's orbit also affects
Earth's centrepital acceleration. The directions of
their forces cancel each other almost perfectly, so
for many purposes they can be and are ignored.
I don't how to describe it both simply and correctly.
If everything outside Earth's orbit was a perfectly
uniform shell, the barycenter of the rest would be
the the nearest thing to an exact focal point of
Earth's elliptical orbit.

-- Jeff, in Minneapolis

2. Order of Kilopi
Join Date
Dec 2004
Posts
11,219
Originally Posted by Noclevername
My understanding is that each of those things have
their own gravitational relationships and thus their
own barycenter.
Yes.

Originally Posted by Noclevername
There is no "barycenter of the Solar System", because
the barycenter is relative to each relationship.
As Hornblower said, there is a barycenter of the Solar
System. I've seen a diagram showing how it changes
over time as the planets move about.

Originally Posted by Noclevername
The Shuttle orbited the barycenter between the Shuttle
and Earth.
This showed that I erred in saying that Earth orbits the
barycenter of the Sun, Mercury, and Venus. It is actually
the barycenter of the Sun, Mercury, Venus, and Earth.

-- Jeff, in Minneapolis

3. The solar system orbits the galaxy in about quarter of a billion years, so our oldest DNA has gone around the galaxy about sixteen times since the origin of life on earth.

The solar system barycenter inscribes a perfect arc around the galaxy, and the sun wobbles from side to side of this path, in a movement primarily driven by the regular patterns of the gas giants. I discuss the movement of the sun against the SSB at http://cosmoquest.org/forum/showthre...f-Solar-System quantifying the effects of the planets.

"Spiral" might not be the best word to describe a helix, as spirals are usually like a clock spring whereas a helix has a constant radius. But helix is seen as a form of spiral, in the sense that the DNA double helix is sometimes said to have a spiral structure.

The movement of the solar system with respect to the galaxy is discussed at these threads
http://cosmoquest.org/forum/showthre...ngle-to-Galaxy
http://cosmoquest.org/forum/showthre...rection-of-sun

4. Originally Posted by Robert Tulip
The solar system barycenter inscribes a perfect arc around the galaxy,
Not really perfect; it bounces up and down through the plane of the Galaxy every sixty-five million years or so, and will be slightly perturbed by other objects in the galaxy; so it will never come back to exactly the same place twice with respect to the Galaxy.

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