Do stars that are relatively nearby, say less than 10 LY, display any motion against the background of stars that are much farther away? Or is our time frame just too short to catch such motion?

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

"Yes", if by "display any motion" you mean that photographs over time within the range of a human lifetime will show that they moved.

"No" if you meant you'll see them move by looking at them, unless you can look at them without averting your eyes or sleeping for a year or so. :^)
The fastest, Barnard's Star, has this note: "The 10.3 seconds of arc it travels annually amounts to a quarter of a degree in a human lifetime, roughly half the angular diameter of the full Moon."

Caveat: I am not astronomer, nor do I play one on TV.

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Well I was figuring a period that would cover an astronomer's career. So that begs another question. Are all nearby stars watched on a regular basis to determine their projected path over the years and are any of them projected for a path through the oort cloud in the next few thousand years?

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

Well I was figuring a period that would cover an astronomer's career. So that begs another question. Are all nearby stars watched on a regular basis to determine their projected path over the years and are any of them projected for a path through the oort cloud in the next few thousand years?

IMO it is very unlikely any stars will go through the oort cloud in that short of time frame.

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Millions are watched and cataloged.

For a good introduction http://en.wikipedia.org/wiki/Proper_motion

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Do stars that are relatively nearby, say less than 10 LY, display any motion against the background of stars that are much farther away? Or is our time frame just too short to catch such motion?

Might have something to do with gravitational lensing. Bending of space and therefore also time as the Universe consists of spacetime, also know as the aether.


http://en.wikipedia.org/wiki/Gravitational_lens

[edit]Otoh, after reading the whole thread, the above has nothing to do with the opening post... :)) Spacetime and gravity do have an influence on any moving object in the Universe is what I think.

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rOZZ
Music
Pictures

When will you guys stop all this silly curvature of spacetime nonsense

It is not nonsense, gravity lensing is used in astronomy.

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When will you guys stop all this silly curvature of spacetime nonsense

It is not nonsense, gravity lensing is used in astronomy.

Considering he just claimed that gravity is caused by the rotation of the Earth's core I think we can ignore Chris' scientific 'advice'

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Reality Internet Personality

If the Earth stopped rotating we wouldn't all fly off into space! but we would weigh less than we do now. But there would be no alternating days and nights, and the tides would be affected.

[off topic]

http://image.gsfc.nasa.gov/poetry/ask/q1168.html

If the Earth stopped spinning suddenly, the atmosphere would still be in motion with the Earth's original 1100 mile per hour rotation speed at the equator. All of the land masses would be scoured clean of anything not attached to bedrock. This means rocks, topsoil, trees, buildings, your pet dog, and so on, would be swept away into the atmosphere.

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As for other effects, presumably the magnetic field of the Earth is generated by a dynamo effect that involves its rotation. If the Earth stopped rotating, it's magnetic field would no longer be regenerated and it would decay away to some low, residual value due to the very small component which is 'fossilized' in its iron-rich rocks. There would be no more 'northern lights' and the Van Allen radiation belts would probably vanish, as would our protection from cosmic rays and other high-energy particles. This is a significant biohazard.

Whether the Earth were to stop spinning suddenly, or slowed to a stop, it would not be good for its inhabitants.

If the Earth stopped rotating we wouldn't all fly off into space! but we would weigh less than we do now. But there would be no alternating days and nights, and the tides would be affected.

[off topic]

http://image.gsfc.nasa.gov/poetry/ask/q1168.html

If the Earth stopped spinning suddenly, the atmosphere would still be in motion with the Earth's original 1100 mile per hour rotation speed at the equator. All of the land masses would be scoured clean of anything not attached to bedrock. This means rocks, topsoil, trees, buildings, your pet dog, and so on, would be swept away into the atmosphere.

...

As for other effects, presumably the magnetic field of the Earth is generated by a dynamo effect that involves its rotation. If the Earth stopped rotating, it's magnetic field would no longer be regenerated and it would decay away to some low, residual value due to the very small component which is 'fossilized' in its iron-rich rocks. There would be no more 'northern lights' and the Van Allen radiation belts would probably vanish, as would our protection from cosmic rays and other high-energy particles. This is a significant biohazard.

Whether the Earth were to stop spinning suddenly, or slowed to a stop, it would not be good for its inhabitants.

Exactly, gravity is nothing to do with the Earth's rotation. We would only fly off because of Newton's 1st law.

Gravity is an attractive force related to the separation of two masses according to Newton's law of Gravitation.

F= GMm/r^2 in the case of the Earth, the two masses would be the mass of the Earth and whatever object we are talking about, e.g. a person. Your weight is the value of the force, F. r is the distance between your centre of mass and the Earth's centre of mass and G is the universal gravitational constant. (6.67 x 10^-11 N m^2/kg^2.).

Your weight (the size of gravitational attraction between you and the Earth) has nothing to do with the spinning of the Earth's core.

Einstein uses the curvature of space-time to model this attractive force quite successfully. The CERN people have been trying to figure out what gives things mass.

Light does bend around gravitational objects and this has been shown via Eddington's famous experiment of 1919. The bending of light because of the curvature of Space-time is a different effect that the everyday bending of light we see due to refraction.

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Reality Internet Personality

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Rotating wheel space stations can create "artificial gravity". Stations

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Artificial gravity is not the same force as gravity. It just creates an acceleration the same as the one that produced by the gravitational force.

Much like a spinning round about. You feel the acceleration because the wheel is spinning, you don't fly off as long as you are holding tight. In the case of the space station you will be stopped from flying off because of the walls of the spaceship. This will feel like gravity. It has nothing to do with gravity and more to do with inertia.

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Reality Internet Personality

Artificial gravity is not the same force as gravity.

Actually in G.R. the Equivalence principle shows the two as the same, with the caveat that it holds true for point-sized samples. (You can tell if your local "gravity" is due to "upwards" acceleration through space or acceleration due to gravity by whether it has tidal falloff by the square of the distance from the hypothesized other mass.)

This equivalence is strong enough that it was used by Einstein to deduce the bending of light rays by gravitational fields. The equivalency is that a beam of light traveling across a room accelerating "upwards" will curve "downwards", so the exact same curve should appear under acceleration due to gravity. That it did was yet another confirmation of G.R.

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Artificial gravity is not the same force as gravity.

Actually in G.R. the Equivalence principle shows the two as the same, with the caveat that it holds true for point-sized samples. (You can tell if your local "gravity" is due to "upwards" acceleration through space or acceleration due to gravity by whether it has tidal falloff by the square of the distance from the hypothesized other mass.)

This equivalence is strong enough that it was used by Einstein to deduce the bending of light rays by gravitational fields. The equivalency is that a beam of light traveling across a room accelerating "upwards" will curve "downwards", so the exact same curve should appear under acceleration due to gravity. That it did was yet another confirmation of G.R.

The equivalence principle says that the acceleration is the same. That is not the same as saying the force is the same.

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Reality Internet Personality

And what's the effect of the Dark Matter Lattice on gravity, mass and all tangible matter?

Why don't the stars at the edge of a galaxy revolve around the center mass at the correct rate (slower than they actually do)?

"There are more things in Heaven and Earth, Horatio........."

:D...g

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"Sour Grapes make a bitter Whine." <(0)>

A gyroscope’s angular momentum resists tipping (rotation about a different axis), so that it can remain stable at an impossible-seeming angle. But it has no additional resistance to falling: it still has to be supported. Put a gyroscope on a scale, and no matter how far it leans over its weight will read the same.

No matter how fast or slow the Earth spins, its gravity remains constant. It used to rotate faster, when the Moon was closer, and given enough time would eventually become tidally locked, making only a few rotations per year—but the dying red-giant Sun will probably vaporize both bodies before that happens.

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