[LeGrande]

Is the lag present when observed from the North or South poles?

It always takes apx. 8.3 minutes for the light to get to the Earth from the Sun. An observer on a pole sees the Sun where it was 8.3 minutes ago.

Let's make the question more interesting : ) Let's say that you are standing on a turntable at the North Pole. Lets also say that the turntable is tracking the Suns gravity field (its actual position). Will the pointer on the turntable be pointing at the light that you see or will it be leading or lagging that light by 2.1 degrees?

Here is another question for you. A sextant is pointed at the Sun from our spinning Earth, then the Earths rotation is stopped (we have an inertia less system). Will the Suns apparent motion immediately stop or will it stop in 8.3 minutes?

Or the question in reverse. You are looking at the Sun in the sky. The Sun is turned off. Will you see the Sun traveling across the sky for another 8.3 minutes or will the Sun appear to stop in the sky for 8.3 minutes until it goes dark?

I am also curious about your answer to my question about your lazer ring gyro?

[mrjesse]

Said LeGrande:It always takes apx. 8.3 minutes for the light to get to the Earth from the Sun. An observer on a pole sees the Sun where it was 8.3 minutes ago.

The observer sure will see the sun where it was 8.3 minutes ago -- but the problem with your reasoning is that since the sun still is (relative to the earth) where it was 8.3 minutes ago, where it is is where it was, and so the light will still appear to come from where the sun is (not considering, of course, the 20 arcseconds from the observer's transverse velocity.)

Let's make the question more interesting : ) Let's say that you are standing on a turntable at the North Pole. Lets also say that the turntable is tracking the Suns gravity field (its actual position). Will the pointer on the turntable be pointing at the light that you see or will it be leading or lagging that light by 2.1 degrees?

If the sun were orbiting the earth, then the pointer would point 2.1 degrees ahead of the apparent position of the sun because the sun would have actually moved 2.1 degrees since the light left it. But since the sun is still where it was 8.3 minutes ago, the light will still be coming from the same place that the sun is - so the arrow will really point at the sun as far as Light-time correction goes (but will appear 20 arcseconds displaced due to the observer's transverse velocity - but 20 arcseconds is nothing compared to 2.1 degrees!)

Is it not true that you believe that the answer to your above question would be "The arrow will point 2.1 degrees ahead of the apparent position of the sun?"

Here is another question for you. A sextant is pointed at the Sun from our spinning Earth, then the Earths rotation is stopped (we have an inertia less system). Will the Suns apparent motion immediately stop or will it stop in 8.3 minutes?

Since the sun neither knows nor cares that the earth is turning, and since it's light radiates in an approximately straight line from sun to earth, and since the sun's apparent position is within 20 arc seconds of its actual position, the moment the earth stopped rotating the sun's apparent motion would also stop.

Is it not true that you believe that the answer to your question would be "The sun would continue to move across the sky for another 8.3 minutes?"

Furthermore, to make the question more interesting, let me slightly modify your above question: what if the sun were 10 light days away, and the earth was suddenly stopped? Is it not true that you believe that the sun would continue to appear to rise and set for another 10 days? What do you think? Does the sun's light wind up around the earth like a tape measure spring just because the earth is rotating in place? Do you believe that at any instant, the path that the sun's light takes to reach the earth spirals around? I mean, if the sun was orbiting the earth, yeah! but the earth pretty much orbits the sun.

Or the question in reverse. You are looking at the Sun in the sky. The Sun is turned off. Will you see the Sun traveling across the sky for another 8.3 minutes or will the Sun appear to stop in the sky for 8.3 minutes until it goes dark?

That's a silly statement - but you asked it. Of course the sun will still appear to move at 2.1 degrees per 8.3 minutes because that's the rate the earth is rotating at. But every last lightwave will strike the earth within about 20 arcseconds of the direction of the sun.

I am also curious about your answer to my question about your lazer ring gyro?


What you're saying basically is "If you operate that laser ring gyro in a way which cannot measure the rotation it will not be able to measure the rotation." But it's not a particularly sound method of making a point to say that a certain tool can never work just because if used incorrectly it won't work.

So - how about answering your own above (and my) questions, just for fun?

Thanks

-Jesse