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I am back. I had to make a quick flight down to LA while the weather window was open.

But as it is, the 2.1 degrees per 8.3 minutes is the rotational rate of the earth - not the orbital rate of the sun. Thus the light will still be traveling in a ~straight line from the sun to the earth, and as a result, the direction from which the light hits the earth will be that of the direction of the sun - in other words, it will appear to be where it is as far as Light-Time correction is concerned.

This is the crux of the whole matter. Mrjesse claims that the suns actual position is where it appears to be from the perspective of a person on the earth. He agrees that if the Sun orbited a stationary Earth, its actual vs apparent position would be off by 2.1 degrees, but he objects to the idea that a spinning earth vs a stationary Sun is equivalent. They are : )

Let me provide another thought experiment : ) Lets say that mrjesse and I are floating around in empty space with radar guns. mrjesses looks at his radar gun and sees that I am approaching him at 10 mph. I look at my radar gun and see that mrjesse is approaching me at 10 mph. What is the reality? Who is really moving? At what speed?

The reality is that all that can be determined, is that the two floaters are coming together at 10 mph. Each floater might be moving to the other at anywhere from 0 to 10 mph. All that can be determined is that the sum of the speed adds up to 10 mph. I might be stationary or mrjesse might be stationary or we might both be moving.

The important point is that it is entirely valid for me to assume that I am stationary and that mrjesse is coming at me and mrjesses can also correctly infer that he is stationary and I am going to him. Trivially, this is the equivalence principle.

Now back to our observer on the earths equator. As far as the observer is concerned, whether the earth is spinning or the Sun is orbiting the earth (or some combination) is equivalent. The observations for the observer will be identical.

The fact is that it takes light apx. 8.3 minutes to get from itself to the observer. If the observer pounds a stake into the ground pointing at the sun, then waits 8.3 minutes and points another stake into the ground pointing directly at the sun, the measured angular difference will be apx. 2 degrees.

What does this little experiment show the observer? A lot of things actually, but for our purposes the second stake is pointing at the suns actual position when the first stake was pounded in the ground pointing at the sun.

MrJesse apparently believes that both stakes are pointing at the suns actual instantaneous position. The only way that could be true is if the speed of light is instantaneous, which of course it isn't.

The ball is in your court mrjesse. Given that we know that it takes light 8.3 minutes to get to our observer on the equator from the Sun, how do you explain that the Sun is exactly where it appears to be if the earth is spinning, but 2.1 degrees off if the Sun is rotating the earth.

>>The ball is in your court mrjesse. Given that we know that it takes light 8.3 minutes to get to our observer on the equator from the Sun, how do you explain that the Sun is exactly where it appears to be if the earth is spinning, but 2.1 degrees off if the Sun is rotating the earth.<<

Just for the record...

Its traditional to think of the sun as fixed with the earth orbiting the sun in a circle while spinning on its axis.

The actually situation is more complicated.

The sun is not fixed; the sun and earth actually orbit each other in an ellipse.The reason we speak only of the earth orbiting the sun is that greater mass of the sun means it doesn’t move nearly as much.

And for the nerds among us:

The sun also rotates on its axis but the tops and middle of the sun rotate at different speed. Every 27 days at the equator but only every 31 days at the poles.

“Mrjesse claims that the suns actual position is within ~0.005833° of where it appears to be from the perspective of a person on the earth.” [excerpt, corrected]

I have corrected your statement to reflect what mrjesse has really said.

“but he objects to the idea that a spinning earth vs a stationary Sun is equivalent. They are : )” [excerpt]

A spinning Earth versus a stationary Sun?

I believe we all agree that the Sun is, relatively speaking, stationary, and that the Earth is spinning.

“Now back to our observer on the earths equator. As far as the observer is concerned, whether the earth is spinning or the Sun is orbiting the earth (or some combination) is equivalent. The observations for the observer will be identical.” [excerpt, bold emphasis mine]

Unless those observations include looking at a Laser Ring Gyro.

The instant you consult the LRG, you know if you are spinning, and how much.

“The fact is that it takes light apx. 8.3 minutes to get from itself to the observer. If the observer pounds a stake into the ground pointing at the sun, then waits 8.3 minutes and points another stake into the ground pointing directly at the sun, the measured angular difference will be apx. 2 degrees.” [excerpt]

That only demonstrates the angular speed at which the Sun goes across the sky.

“What does this little experiment show the observer? A lot of things actually, but for our purposes the second stake is pointing at the suns actual position when the first stake was pounded in the ground pointing at the sun.” [excerpt]

Only if the Sun orbits the Earth.

“MrJesse apparently believes that both stakes are pointing at the suns actual instantaneous position. The only way that could be true is if the speed of light is instantaneous, which of course it isn't.” [excerpt]

You have misconstrued mrjesse's position beyond correction.

“The ball is in your court mrjesse. Given that we know that it takes light 8.3 minutes to get to our observer on the equator from the Sun, how do you explain that the Sun is exactly where it appears to be if the earth is spinning, but 2.1 degrees off if the Sun is rotating the earth.” [excerpt]

Once again, this is an inaccurate representation of what mrjesse has been saying.

Said LeGrande:I am back. I had to make a quick flight down to LA while the weather window was open.

Welcome back! how was the flight?

This is the crux of the whole matter. Mrjesse claims that the suns actual position is where it appears to be from the perspective of a person on the earth. He agrees that if the Sun orbited a stationary Earth, its actual vs apparent position would be off by 2.1 degrees, but he objects to the idea that a spinning earth vs a stationary Sun is equivalent. They are : )

The reason a spinning earth and orbiting sun aren't equivalent is because the light emitted from the sun, once set on its course, stays on course even if the sun moves. So if the earth is rotating, the sunlight which hits the earth will be between the sun and the earth on its 8.3 minute journey. But if the sun is orbiting the earth once every 24 hours instead of the earth rotating, then by the time the sunlight reaches the earth, the sun will have moved 2.1 degrees and the light won't be coming from the direction of the sun anymore - and will no longer be exactly between the sun and the earth at all times of its travel. (This would be easier to see if the earth were 12 light hours away from the sun.)

Now back to our observer on the earths equator. As far as the observer is concerned, whether the earth is spinning or the Sun is orbiting the earth (or some combination) is equivalent. The observations for the observer will be identical.

Yeah, unless there's a third body in the works that marks where the sun used to be (like the light that it emitted) -- then all of the sudden it makes a difference whether the sun moved or not :-)

The fact is that it takes light apx. 8.3 minutes to get from itself to the observer. If the observer pounds a stake into the ground pointing at the sun, then waits 8.3 minutes and points another stake into the ground pointing directly at the sun, the measured angular difference will be apx. 2 degrees.

This indicates only the rate - and has nothing whatsoever to do with the instantanious angular displacement between actual and apparent position. This same experiment would give the exact same results regardless of how much lagged the sun was or how many light minutes it was away -- as long as the rate was 2.1deg/8.3minutes.

What does this little experiment show the observer? A lot of things actually, but for our purposes the second stake is pointing at the suns actual position when the first stake was pounded in the ground pointing at the sun.

Again, this only demonstrates rate - not instantanious angular displacement.

MrJesse apparently believes that both stakes are pointing at the suns actual instantaneous position.

I believe no such thing! I have always "admitted" (more like freely and cheerfully stated) that the earth rotates at 2.1 degrees per 8.3 minutes.

The only way that could be true is if the speed of light is instantaneous, which of course it isn't.

The ball is in your court mrjesse.

If the ball is in my court then how come you won't answer my question? specifically this one?:

For an observer on earth at an instant in time who was looking at a relatively (to earth) stationary and bright planet which was above the equator (of earth) and was 12 light hours away -- where would it appear as compared to where it was? Would it's gravity really pull east while it's light came from the west? Simple question.

The ball is not in my court. I answer your questions and you just ask more, often not even answering your own (but I do hope you will answer your own in that other post in which I asked you to answer your own!)

Given that we know that it takes light 8.3 minutes to get to our observer on the equator from the Sun, how do you explain that the Sun is exactly where it appears to be if the earth is spinning, but 2.1 degrees off if the Sun is rotating the earth.

Like I already said - if the sun is not moving, then the light will appear to come (within 20 arc seconds) from where the sun is because the sun is still where it was 8.3 minutes ago. But if sun has moved 2.1 degrees since emitting said light, then it won't be where it was by the time its light hits the earth, so the light will come from where the sun was (but no longer is) because that's where the sun was when it emitted it.

You've got to understand that the path of light from the sun does not contort itself just because the earth is rotating!

And by the way, if you think I'm making this up just search google (or your favorite library) for the term "Stellar Aberration" and "Light-time Correction" and you will see that it most certainly does matter whether the motion is on the part of the observer or the emitter. Light-time-correction is the apparent angular displacement caused by a distant and moving light emitter (and is a function of distance and emitter transverse velocity), and Stellar Aberration is the apparent angular displacement due to the transverse velocity of the observer - and is not affected by distance to the light source.

So how about answering my question? Thanks!

-Jesse

(Repeated here for clarity - my question:)

For an observer on earth at an instant in time who was looking at a relatively (to earth) stationary and bright planet which was above the equator (of earth) and was 12 light hours away -- where would it appear as compared to where it was? Would it's gravity really pull east while it's light came from the west? Simple question.