Star trails and the Earth's movemement

[mfb]

Yes, the camera rotates as it moves laterally with the earth.

That part is completely irrelevant. All the change in position of the camera is irrelevant over a few hours.

The change in camera orientation is the important point. It is something you can literally see within a few seconds with your eyes, right where you are. And you keep ignoring it.

 

[UsableThought]

If the stars are too far away, then why do we see any motion from our fixed point at all? And because we see motion, why is it only the rotation and not the much faster lateral orbit motion?

If I had to recreate this scenario in Autocad, how would I possibly end up with what we see in real life star-trails? It would be an impossible model. If the Earth spins on the spot, looking at distant objects, I will get circles. If the Earth spins and moves laterally, spiraling streaks. You can't have it both ways.

@hamischism, just to pile on to the answers already given - How do you explain that Polaris has for centuries been relied on as the "North Star" for marine navigation? If your talk of "spirals" were valid, sailors would not be able to treat Polaris as a fixed point. But they do. To quote Wikipedia:

Because Polaris lies nearly in a direct line with the axis of the Earth's rotation "above" the North Pole—the north celestial pole—Polaris stands almost motionless in the sky, and all the stars of the northern sky appear to rotate around it. Therefore, it makes an excellent fixed point from which to draw measurements for celestial navigation and for astrometry.

Something else strikes me as odd. You have admitted we don't see spirals; but when people attempt to explain why, you reject their answers & insist that we ought to be seeing spirals. Eh?

 

[Doc Al]

b) Moving sideways at 67 times this rotational speed.

Ignore the Earth's rotation for a moment. Please calculate the apparent angular velocity of Polaris that you'd expect due to the lateral motion. (Then compare that to the Earth's angular velocity.)

 

[hamischism]

@hamischism, just to pile on to the answers already given - which for some reason you can't grasp, I don't know why: How is it that Polaris has functioned for centuries as the North Star for navigation? Why have sailors never once complained about seeing "spirals"?

To quote Wikipedia:

Ever tried making a time-lapse sequence from a boat? It's a blurry mess.

 

[UsableThought]

Ever tried making a time-lapse sequence from a boat? It's a blurry mess.

What on Earth does that have to do with anything I said, or with the point of this thread?

 

[hamischism]

Ignore the Earth's rotation for a moment. Please calculate the apparent angular velocity of Polaris that you'd expect due to the lateral motion. (Then compare that to the Earth's angular velocity.)

I get what you're talking about, but please forget about polaris for a second. I shouldn't have mentioned that star, because it would be the only star whose motion could be plausible - if Earth's axis is always pointed directly at it.

 

[Doc Al]

I get what you're talking about, but please forget about polaris for a second. I shouldn't have mentioned that star, because it would be the only star whose motion could be plausible - if Earth's axis is always pointed directly at it.

Pick any star you like! How about Sirius.

 

[hamischism]

That part is completely irrelevant. All the change in position of the camera is irrelevant over a few hours.

The change in camera orientation is the important point. It is something you can literally see within a few seconds with your eyes, right where you are.

We might need to go 3D on this one to make sure we're on the same page. I just don't see how this will work in any modeling software. We will see star circles with the Earth spinning on the spot, or spirals with the Earth moving laterally and spinning.

 

[Drakkith]

After 3 pages and 43 posts I think it's time to close this thread. Hamischism, please re-read the answers in this thread several times and perform some of the recommended math. It should become apparent what is happening.

Thank you everyone for your contributions.

Thread locked.