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In another thread, in General Astronomy & Cosmology, the baricentre (or barycenter, for those in the US) was mentioned.
Here are the relevant statements:
Does the baricentre 'wobble'? If so, how and why? If not, why not?
Here are the relevant statements:
Let's simplify things a bit; let the mass of our BH be Msun, and let's write our distances as multiples of 100au. At a distance of 16 (= 1600 au), our BH would have an Einstein radius of 1" (and a crossing time of 40ks, ~11 hours).
From context, I assume that "baricenter" is the center of the star being lensed, but since any star seen from Earth (other than sun) is a "point" I am not sure.
The solar system baricentre (or barycenter, to those who live in the US) is its centre of mass. [...] How about you do a simple calculation for us, BillyT? Assume the only massive objects in the solar system are the Sun and Jupiter, that the mass ratio is 1:1000, and that the distance between the centres of these two objects is 800 million km. Where would the 'solar system baricentre' be?
Thanks for the definition.
Because of the 1:1000 ratio, the distance from the sun, I'll call it X, is approximately 0.8 Million Km along the line joining them, and dos ont move as both orbit it. More accurately, 1000X = (800 - X) is sovled to find the distance from the sun.
[...]
I note that in the two only object case you gave, the Baricenter does not "wobble" because these two are orbiting it, but has velocity relative to fixed stars as our solar system "orbits" the the galaxy center (Orbits in quotes as there must be very slight perturbations as other near by stars distrube this orbit.) If there were three (or more) objects it would bve rare that the baricenter was on the line joining any two, and never if the orbit planes were not the same.
Indeed; the baricentre does not 'wobble', by definition!
I think this is an interesting discussion, but completely OT for the original thread.Either I don't understand you or you are wrong on this, assuming "baricenter" is just a new (to me) term for "center of mass."
For example, in your two body case (Sun and Jupiter only), the baricenter is always in the plane of Jupiter's orbit; but now let us add Pluto, which is rarely in this plain. When Pluto is "above" (North or what ever is the correct term), then the baricenter is also slightly above (North) of the "Jupiter ecliptic." Conversely when Pluto is "below" (South), then the baricenter is also slightly South of the "Jupiter ecliptic." - This oscillation above and below the "Jupiter ecliptic" is what I was referring to as "wobble." Any third body, not in "Jupiter's ecliptic," will cause this wobble, Mercury with the shortest oscillatory period and the passing of a near by star, with such a long one that only a few oscillations have occurred in the history of the universe.
I don't see how you can define away this real effect and yet keep the meaning of the "baricenter" the same as the "center of mass."
Does the baricentre 'wobble'? If so, how and why? If not, why not?