PDA

View Full Version : Earth does not fly off at a tangent due its high speed in many frames of reference



neilzero
2013-May-20, 07:22 PM
The Earth orbits the Sun at the correct speed for the shape of Earth's orbit.
The Sun orbits at the correct speed for the shape of it's orbit though our galaxy.
I suspect the black hole at the center of our galaxy accounts for a few percent of the Sun's speed and orbit. Possibly dark matter is the largest factor.
I see the title needs two more applications of the space bar, but I can't edit the title. Neil

Mod edit: I've restored a previous version of this edited post because the following post by antoniseb depends upon the context. The third sentence was edited to read:
"I suspect the black hole at the center of our galaxy accounts for a few percent/No a few parts per 100,000 of the Sun's speed and orbit. Possibly dark matter is the largest factor."

antoniseb
2013-May-20, 07:28 PM
Sgr A* has a mass of 4 million times the mass of the Sun. The galaxy inside the orbit of the Sun might b 50,000 times more than that... so a lot less than a few percent. Dark Matter is the bulk of the gravity determining the Sun's orbit.

tusenfem
2013-May-20, 07:33 PM
I have no idea what the title or the OP is supposed to mean.

Glom
2013-May-20, 10:20 PM
The galaxy cannot really be likened to the two body problem because it is a fluid cloud if stars. Most certainly Old Munchy can't be considered the principle attractor analogous to the Sun in the solar system.

Shaula
2013-May-21, 05:21 AM
Even if it were 100% the black hole it would still not affect the Earth/Sun's speed - it would affect their velocity. Very important distinction.

Grey
2013-May-21, 05:57 PM
Is there an actual question that you'd like answered?

Hornblower
2013-May-21, 06:17 PM
Even if it were 100% the black hole it would still not affect the Earth/Sun's speed - it would affect their velocity. Very important distinction.Speed is the scalar magnitude of the velocity vector, and gravity will cause it to change unless the gravitational vector is perpendicular to the velocity vector.

Hornblower
2013-May-21, 06:18 PM
The Earth orbits the Sun at the correct speed for the shape of Earth's orbit.
The Sun orbits at the correct speed for the shape of it's orbit though our galaxy.
I suspect the black hole at the center of our galaxy accounts for a few percent of the Sun's speed and orbit. Possibly dark matter is the largest factor.
I see the title needs two more applications of the space bar, but I can't edit the title. Neil

Mod edit: I've restored a previous version of this edited post because the following post by antoniseb depends upon the context. The third sentence was edited to read:
"I suspect the black hole at the center of our galaxy accounts for a few percent/No a few parts per 100,000 of the Sun's speed and orbit. Possibly dark matter is the largest factor."

I don't understand either the title or your comment about it. Could you clarify, please?

caveman1917
2013-May-22, 11:18 AM
The galaxy cannot really be likened to the two body problem because it is a fluid cloud if stars.

You can get close to a two-body analysis by application of the shell theorem.

Ken G
2013-May-26, 01:52 PM
I never really understood using the shell theorem in the galaxy, by the way, because it only applies for spherically symmetric mass distributions. The galaxy does have a nearly spherical "bulge", but by the time you get to the Sun's orbit, there must be a lot of stars in the disk that are contributing significantly. So it always seemed like a bit of a stretch to apply the shell theorem, but perhaps it's just a case of "you want the truth, you can't handle the truth" so we settle for a reasonable approximation. The problem isn't the "two body" nature (in fact a two-body problem is just like a one-body problem, which only requires knowing the gravitational field), the problem is that the field of a disk+bulge is complicated.