Only the celestial south pole has to be visible at every single location in the southern hemisphere at the same time. The Southern Cross is not the celestial pole and therefore it is not visible everywhere in the south at the same time. Nobody says it should be. (see #103 for detailed explanation).
It only often serves as orientation to find the celestial pole because it is remotely close to it.
Same goes for the northern constellations. Everybody capable of LOOKING UP during the night should clearly see that not all the northern constellations are visible at the same time!
Sigma Octantis is the star closest to the southern celestial pole. It is a bit harder to see than Polaris because it's much fainter, but this one you CAN see from every point in the southern hemisphere at the same time (provided it's nighttime of course).
#101 False claim
Again, nobody claims that Sigma Octantis is sitting exactly on the southern celestial pole. Nobody says that. It's only the CLOSEST star to the pole. That's why it moves! (Just like Polaris)
At nighttime, there are three people in Brazil, South Africa and Australia. Have them look due south at the same time, looking up at an altitude equal to their latitude. Everybody sees Sigma Octantis at the very same time in this position, only with the tiny offset which is its distance to the celestial pole (roughly 1°).
It CAN be seen using "publicly available telescopes"! Even with binoculars. You only have to be in the south and go to a dark place because it's faint! In a very dark place it is even visible to the naked eye. Only people who have never tried this can speculate on that.
#102 False claim
First and foremost, every star's declination can be measured and verified through geographical latitude and rotation. Geographical latitude can be measured and verified by simply looking at the celestial pole. That also remains measurable and verifiable for either side of the globe, at any time of year, at any time of night, for every location in the world.
The following video provides a very simple explanation, why this is impossible on a flat earth:
(be warned, though, contains harsh language)
Furthermore, if this fantastic vanishing point existed, it would be impossible to see airplanes further away than the horizon flying visibly close to the horizon and there would be no valid explanation for radar (radiowaves, also a form of light, but not in the visible spectrum) being able to pierce through clouds and show us the shape of airplanes or even the moon, whereas it fails to show us any kind of landscape beyond the horizon. Radiowaves can travel through clouds, penetrate meter-thick brick walls, but for some odd reason have a terrestrial range limit..
#103 Incomprehension of the model
The consequence of a star’s declination is that at some point during the night it will run exactly through the zenith (highest point in the sky) of a given location with the same geographical latitude as the declination. When the star reaches that point, it is only logical that on a sphere you had to go at least 90° away from your point of observation for it to be invisible (obscured by earth).
The southermost star of Ursa Major (AKA “Big Dipper + a little more”) is Tania Australis. It has a declination of roughly +41.5. Look at the night sky from Cleveland, Ohio (41.5°N). At some point during the night (or day depending on season), Tania Australis will go exactly through the zenith from your point of observation. And that means, in order to NEVER be able to see it, you have to go down at least 90° further south, which gives you roughly 48.5° South.
The northermost star of Ursa Major “h UMa” has a declination of roughly +63°. So in order to never be able to see it, you have to go down to roughly 27° South. Most stars of this constellation lie under +60°. That gives you the value of 30°S, where Mr. Dubay claims it should be obscured by “thousands of miles of bulging Earth”.
I’m guessing the two factors he didn’t take into account were the earth’s rotation and the different span of arc that each constellation has. When you’re standing in, say, Johannesburg (28°S), and following the above argumentation, Ursa Major should not be visible all the time, but at some point it will be ROTATING INTO YOUR VIEW. Let’s observe the night sky from Johannesburg, looking due north:
There it is, Ursa Major including the “big dipper” can be seen clearly, only with its northermost star barely obscured (keep in mind, JoBurg is at 1783m elevation). That’s exactly what the spherical model predicts.
(Credit goes to "Stellarium" for the above photos)
#104 Incomprehension of the model
Again, as in #103, Mr. Dubay failed to include the earth's rotation and the constellations span of arc into his "logic".
Vulpecula has a declination roughly between +20° and +30°. With its lowest declination of +20° it can be seen anywhere north of °70N all the time. Subtracting 90° to the south will give you the southermost place, where it will rotate into view at some time. At 60°S it can be still entirely visible, at 70°S it's completely gone. These are the roughly 65°S that Mr. Dubay claims to be impossible..
Same goes for Taurus (between -1° and +30°), Pisces (-6° to + 34°) and Leo (-7° to +33°). Wikipedia puts their "average" declination between +15 and +19, which I think is an unnecessary abbreviation, as it doesn't display the 40°-arc that Pisces and Leo describe (declination-wise).
65°S is therefore not an exact value for these three. For possible complete visibility (at times) it's rather 60°S for Taurus (up to 89°N), 56°S for Pisces (to 84°N) and 57°S (to 83°N) for Leo. However, since most of their brightest and defining stars lie roughly in the middle between their min- and max declinations (broadening the field by 5 to 10°), 65°S and 90°N is still an OK rule-of-thumb value.
#105 Incomprehension of the model
How many more of these..? Aquarius (-25° to +3°), Libra (-30° to -1°), Virgo (-22° to +14°) and Orion (-11° to +23°), alright. In #103 & 104 I've already shown the geometry & math involved. So, correct me if I'm wrong, here are just the more exact values for POSSIBLE (keep in mind: Periodic, not continous) complete visibility of these four:
Aquarius: 65°N to 87°S
Libra: 60°N to 90°S
Virgo: 68°N to 76°S
Orion: 79°N to 67°S.
As previously explained, these values are not only possible, they are a direct and logical consequence of terrestrial and celestial geometry.
And as shown in the video in #102, this is entirely impossible on a flat earth.
#106 Incomprehension of the model
Nobody claims that there is ONE actual South Pole. That is complete nonsense, nobody says that! There is one geographical south pole, as defined through the earth's shape and it's movement and there is a south magnetic pole, defined though the earth's magnetic field. There is a geophysical relation between the two (explained by the earth's rotation), but they are not the same!
#107 Incomprehension of the model
Sitting on a ring magnet would produce the exact same effect that Mr. Dubay wrongly expects to happen on a globe (see#108):
Oh, and concerning the fact that we never have "penetrated through beyond the crust": That is absolutely true. However, hearing your flatmate have loud sex in the neighboring room doesn't require you to penetrate through the wall, does it? You kind of get the idea of what is going on without having a need to go there and look. Geiger counters do the exact same thing. When there's an earthquake, they can tell us where there's something going on, where the shock waves go, how fast and strong they are and how they dissipate.
Conducting experiments of our own that reproduce the expected conditions that correlate with our "observations" and thus enabling ourselves to make working predictions, can establish quite a sound model of what is actually happening down there..
I just made geophysics sound really sexy, didn't I..? :-)
#108 Incomprehension of the model
Nobody says that compasses always point towards the poles. They align along magnetic field lines. When you place a compass at equal distances to both ends of a bar magnet, the compass needle will not point at one pole, but will align itself parallel to the magnet. That only works with two poles establishing a magnetic field:
The concept of earth's magnetic field only takes that into the third dimension:
#109 Incomprehension of geometry
It just doesn't work. Circumnavigating earth at the equator you see Polaris due north and exactly at 0° altitude (horizon-level), whereas at the North Pole it is at exactly 90° overhead. And every other star that you have to take into account during that circumnavigation absolutely makes no sense on a flat earth. Everybody circumnavigating the earth at the equator finds Sigma Octantis at 0° due south, and everybody doing it on the tropic of Capricorn sees it at 23.5°, due south and at the same time.
And now, factoring in the star's rotation, it becomes an even bigger mess because on a flat earth you would get opposing directions being cut off at the equator. This is just wrong on so many levels..
Look at the video in #102.
There is just NO WAY to explain this other than on a globe. I already posted a 100$-challenge on youtube asking for a flat map of earth that can solve this problem. I didn't get an answer because I don't think there is a solution.