[Yamato]

Found in this thread, pizaaplanet points us to a video made by Rory Cooper that explains about how the stars move (or seem to move) in the firmament.

The video is the next one:

https://www.youtube.com/channel/UCyNPWFz40XeHT2pWAwoSD3g


Most of the video is wrong because it has some terrible errors that doesn't match what we observe everyday.

First, the video assumes that the earth is flat, which is an assertion that cannot be demonstrated, making the rest of the video invalid (you cannot state something as truth if you start from a hypothesys that you cannot demonstrate).

But even if we don't have this into account, Rory Cooper commits a serie of errors that made the video invalid no matter what you try to accept, since those errors aren't, by far, what the reality shows us.

First, at 0:44 he asumes that the earth is standing still, which is, again, an assertion that isn't demonstrated, making again the whole video invalid.

Next, in 0:58 he shows us several hypothesys why the stars move or seem to move. The only possibilities are that the observer is over a spinning earth or the stars are spinning. But since he stated before that the earth is standing still, he is contradicting himself by saying now that the earth can spin.

But now, at 1:16 negates something that is actually happing, and can be evidenced by anyone: he states that the stars must be spinning around the earth's rotation axis, which is what we can see if we travel to the north pole.

If we travel to the north pole and record the stars movement above our heads, we will see this:




Which is perfectly correct and doesn't represent any contradiction between our round earth theories and what we can observe.


But now, if we travel closer to the equator, but still in the northern hemisphere, the thing changes.
If we look at Polaris from our new location, we well see the next:





And actually, this is truth since if you travel from, lets say, Sahara Desert to North Sweeden, you will clearly see that Polaris (and every star) seem to be higher (or lower) above the horizon.

I was not in Sahara Desert, nor in Sweeden, but I was in Morocco and in North of UK, and the diference between the possition of stars in both places are clearly noticeable.

Now you may guess how this can happen.
The most plausible answer is this, which, in fact, matches all observations:




Let me explain what this diagram means:

We are first observing the night sky in the north pole. It doesn't mind if the earth is standing still or rotating, or are the stars who move.
If we look to polaris, we will see it just above our head because we are just in the movement axis, and everything star will seem to rotate around Polaris (actually not exactly Polaris).

Now, lets travel to closer to the Equator but still in Northern hemisphere (the red astronomer in the diagram). To see Polaris, we will need to face towards the movement axis, which is in the North Pole. Now, we can observe that Polaris appears way lower in the horizon.
We will see the stars spinning anyway, so I can't see any contradiction between a Round Earth and how stars seem to move in the sky.



Now, at 2:15 Rory Cooper says that some people stated that it is possible to see stars from the north and south hemisphere from the equator. The only possible way is the earth being a plane. But in this case, I will be able to see south stars from anywhere above the equator, which is not possible.
But, if you travel to the equator in a round earth, thanks to different earth movements, it is possible that the most southern stars and northern stars are visible during different seasons, of course, not during the same day.


At 2:47, Roory Cooper starts to talk about the universe as a time piece to measure the months, years, etc.., but you cannot universally measure something that is relative.

Also without having into account that the concept of time is something abstract that was created by the humans to measure and take account of events that happen regularly. Talking about time is completely and utterly pointless.

I can even say that time is just a concept like "love" or "hate", that doesn't have any impact in the reality, nor it is related to any universal physical fact or object, not even can be measured by any means.



At 3:09 Rory Cooper states that the moon is too far to see any kind of detail, which is an statement without demonstration or any other kind supporting data.


So, taking all those true facts I exposed before, Rory Cooper's video is wrong, away from the reality and terribly confusing.

[rottingroom]

I think Rory's biggest refutation was that observing from the north pole would give a time lapse that we all know and understand and that that is all well because the observer is spinning but that anywhere south of that should have some other movement apart from what can be achieved by a spinning action.

While he makes a valid point, it falls apart when one considers just how far away the stars are. Polaris for example is 433 lights years away and compared to the 7918 mile (earth diameter) difference that an observer would see when comparing their observation from one side of the earth and then the other 12 hours later, this is next to nothing. It would be like trying to detect a difference in apparent position of a golf ball on a football field by moving your head by an inch.

[Yamato]

I think Rory's biggest refutation was that observing from the north pole would give a time lapse that we all know and understand and that that is all well because the observer is spinning but that anywhere south of that should have some other movement apart from what can be achieved by a spinning action.

While he makes a valid point, it falls apart when one considers just how far away the stars are. Polaris for example is 433 lights years away and compared to the 7918 mile (earth diameter) difference that an observer would see when comparing their observation from one side of the earth and then the other 12 hours later, this is next to nothing. It would be like trying to detect a difference in apparent position of a golf ball on a football field by moving your head by an inch.

Yes, but it is not that small if you talk about astronomical distances, for example, if you want to study some binary or multiple star system that you need to take very long exposure photographs with a high magnification, then you need to take what you say into account to avoid errors.
In case that you are not familiar with this, good telescopes have a system to point the telescope exactly to the north celestial pole from your location.

[rottingroom]

I think Rory's biggest refutation was that observing from the north pole would give a time lapse that we all know and understand and that that is all well because the observer is spinning but that anywhere south of that should have some other movement apart from what can be achieved by a spinning action.

While he makes a valid point, it falls apart when one considers just how far away the stars are. Polaris for example is 433 lights years away and compared to the 7918 mile (earth diameter) difference that an observer would see when comparing their observation from one side of the earth and then the other 12 hours later, this is next to nothing. It would be like trying to detect a difference in apparent position of a golf ball on a football field by moving your head by an inch.

Yes, but it is not that small if you talk about astronomical distances, for example, if you want to study some binary or multiple star system that you need to take very long exposure photographs with a high magnification, then you need to take what you say into account to avoid errors.
In case that you are not familiar with this, good telescopes have a system to point the telescope exactly to the north celestial pole from your location.

I don't disagree with that. I'm staying on topic by pointing out Rory's error.

He thinks that there should be more motion than what is cause by spinning because 1) during a day your position relative to an imaginary "fixed" earth changes and 2) during a year your position also changes.

While these changes in position are enormous, they are insignificant compared to the distance to stars. Rory made no mention of using precise telescopes to support his claims. He is suggesting that we should be able to intuitively sense these differences because 7918 miles (earths diameter) and 1.23653e8 miles (earths orbital plane diameter) are impressive numbers, but it turns out that as impressive as those numbers may be they are negligible when compared to the distance to stars.

[Yamato]

I don't disagree with that. I'm staying on topic by pointing out Rory's error.

I already agreed with you. And I never said you where offtopic.

He thinks that there should be more motion than what is cause by spinning because 1) during a day your position relative to an imaginary "fixed" earth changes and 2) during a year your position also changes.

And this is the reason why I mentioned the telescope thing. Not to invalidate your argument, which is correct, just as a side note.

While these changes in position are enormous, they are insignificant compared to the distance to stars. Rory made no mention of using precise telescopes to support his claims. He is suggesting that we should be able to intuitively sense these differences because 7918 miles (earths diameter) and 1.23653e8 miles (earths orbital plane diameter) are impressive numbers, but it turns out that as impressive as those numbers may be they are negligible when compared to the distance to stars.

I can't disagree.

Now, as a side note, there are many binary and multiple star systems that are extremly close from our point of view. With a cheap telescope, you can't see them because either the telescope lacks resolution power or the telescope doesn't supports enought magnification to allow you to see them. In this case, you need a very good telescope, with a large aperture (diameter) that gives you a great resolution and supports a very high magnification.

Now, magnification doesn't mean "how big you see things", but rather "how close you see things", so if you use high magnifications, such as x800 (e.g. camera with apparent magnification of x200 and Barlow x4) or even more, the slightest movevent becomes very noticeable.

But this is just a side note. Just that.