[LeGrande]

magine,if you will, that the sun was always just above the horizon for you, all day long and there was no night and the earth didn't spin: If someone built a tall tower and put up a large shutter to block the sun from you, then removed the shutter, there would be a delay when the light started reaching you again, but the light would still be coming from the same direction as always.

Ahh but the earth is spinning and the spin changes the angle of the apparent position.

By the way, I still want to know if you're attributing the 2.1 degrees of apparent position lag of the sun to Time Light Correction or Stellar Aberration.

Primarily the time light correction and spin. The Stellar Aberration only plays a small part at these distances and has factored out the earths spin.

[mrjesse]

Primarily the time light correction and spin. The Stellar Aberration only plays a small part at these distances and has factored out the earths spin.

So do you agree then that Stellar Aberration's effect is almost nothing compared to the 2.1 degrees and therefore we can ignore it while discussing a lag of 2.1 degrees?

By the way, you first said Stellar Aberration, and you illustrated the same, all the while talking about the time of flight from sun to earth of light, but Stellar Aberration has nothing to do with the distance from sun to earth. Had you just confused the two terms (like I did in a recent post) or was that just ignorance? I would hope that when recounting the snow-falling experiment you'd have noticed that it was the wrong principle. What was that all about? Did you think I wouldn't notice the difference?

Thanks,

-Jesse

[mrjesse]

Ahh but the earth is spinning and the spin changes the angle of the apparent position.

I'm not seeing the scientific reason that it should change by the 2.1 degrees you're taking about. 20 arcseconds to be sure, due to Stellar Aberration, but not 2.1 degrees for any reason whatsoever. By the way, regarding Stellar Aberration, the speed through space at which the earth moves as it orbits the sun is about 60 times greater then the surface speed of the earth due to its rotation.

Primarily the time light correction and spin. The Stellar Aberration only plays a small part at these distances and has factored out the earths spin.

See this note here on WP for a clue:

^ Annual aberration is the ratio of Earth's orbital velocity (around 30 km/s) to the speed of light (about 300,000 km/s), which shifts the Sun's apparent position relative to the celestial sphere toward the west by about 1/10,000 radian. Light-time correction for the Moon is the distance it moves during the time it takes its light to reach Earth divided by the Earth-Moon distance, yielding an angle in radians by which its apparent position lags behind its computed geometric position. Light-time correction for the Sun is negligible because it is almost motionless during 8.3 minutes relative to the barycenter (center-of-mass) of the solar system.

Notice that the moon does have light-time correction and apparent angular displacement -- because it does orbit the earth. The sun, on the other hand, does not orbit the earth, and as a matter of fact doesn't move all that much in 8.3 minutes, (no where near 2.1 degrees!)

I'm telling you, it does make a difference whether the earth is rotating at 1 turn per 24 hours or the sun orbiting the earth at 24 hours per orbit.

The light in the Ring Laser Gyro knows whether the earth is spinning and the light coming from the sun knows whether the sun is orbiting!

Thanks,

-Jesse