Aurorae are visible light phenomena observed in the night sky, mostly at high latitudes corresponding to Arctic and Antarctic regions. An aurora can appear as an indistinct glow from a distance or as distinct shifting curtain-like formations of light, in various colours, when seen from nearby.
Aurorae are caused by the impact on Earth’s atmosphere of charged particles streaming from the sun, known as the solar wind.
The Earth’s magnetic field captures the particles and deflects them (according to the well-known laws of electromagnetism) so that they spiral downwards around magnetic field lines. The result is that the particles hit the atmosphere near the Earth’s magnetic poles.
The incoming high energy particles ionise nitrogen atoms in the upper atmosphere, as well as exciting oxygen atoms and nitrogen molecules into high energy states. The recombination of nitrogen and the relaxation of the high energy states results in the emission of photons. The light is produced between about 90 km and 150 km above the surface of the Earth, as shown by triangulating the positions of aurorae from multiple observing locations.
Observations of aurorae have established that they occur in nearly-circular elliptical rings of width equivalent to a few degrees of latitude (i.e. a few hundred kilometres), usually between 10° and 20° from the Earth’s magnetic poles. These rings, in the northern and southern hemispheres, are called the auroral ovals.
The auroral ovals are not precisely centred on the magnetic poles, but rather are pushed a few degrees towards the Earth’s night side. This is caused by the diurnal deflection of the Earth’s magnetic field by pressure from the charged particles of the solar wind.
The auroral ovals also expand when solar activity increases, particularly during solar storms, when increased particle emission from the sun and the resulting stronger solar wind compresses the Earth’s magnetic field, forcing field lines to move away from the poles.
But despite these variations, the auroral ovals in the northern and southern hemispheres move and change sizes more or less in unison, and are always of similar size.
You can see the current locations and sizes of both the northern and southern auroral ovals as forecast based on the solar wind and interplanetary magnetic field conditions as measured by the Deep Space Climate Observatory satellite at https://www.spaceweatherlive.com/en/auroral-activity/auroral-oval.
Earth is not the only planet to display aurorae. Jupiter has a strong magnetic field, which acts to funnel the solar wind towards its polar regions in the same way as Earth’s field does on Earth. Jupiter we can establish by simple observation from ground-based telescopes is close to spherical in shape and not a flat disc. Auroral ovals are observed on Jupiter around both the northern and southern magnetic poles, exactly analogously to on Earth: of close to the same size and shape.
Similar auroral ovals are also seen on Saturn, in both the northern and southern hemispheres [3][4]. And just for the record, Saturn is also easily shown to be spherical in shape, and not a flat disc.
Now, we have established that auroral ovals appear on three different planets, with the southern and northern ovals of close to the same sizes and shapes on each individual planet. Everything is consistent and readily understandable – as long as you assume that the Earth is spherical like Jupiter and Saturn.
If the Earth is flat, however, then the distributions of aurorae in the north and south map to very different shapes and sizes – with no ready explanation for either the shapes or their differences. In particular, large parts of the southern auroral oval end up being extremely far from the southern magnetic pole, in defiance of the electromagnetic mechanism that causes aurorae in the first place.
So the positions of aurorae on a flat Earth cannot be readily explained by known laws of physics, and they also do not resemble the locations and sizes of auroral ovals as observed on other planets. All of these problems go away and become self-consistent if the Earth is a globe.
References:
[1] Safargaleev, V., Sergienko, T., Nilsson, H., Kozlovsky, A., Massetti, S., Osipenko1, S., Kotikov, A. “Combined optical, EISCAT and magnetic observations of the omega bands/Ps6 pulsations and an auroral torch in the late morning hours: a case study”. Annales Geophysicae, 23, p. 1821-1838, 2005. https://doi.org/10.5194/angeo-23-1821-2005
[2] Grodent, D.,Clarke, J. T., Kim, J., Waite Jr., J. H., Cowley, S. W. H. “Jupiter’s main auroral oval observed with HST‐STIS”. Journal of Geophysical Research, 108, p. 1389-1404, 2003. https://doi.org/10.1029/2003JA009921
[3] Cowley, S. W. H., Bunce, E. J., Prangé, R. “Saturn’s polar ionospheric flows and their relation to the main auroral oval”. Annales Geophysicae, 22, p.1379-1394, 2004. https://doi.org/10.5194/angeo-22-1379-2004
[4] Nichols, J. D., Clarke, J. T., Cowley, S. W. H., Duval, J., Farmer, A. J., Gérard, J.‐C., Grodent, D., Wannawichian, S. “Oscillation of Saturn’s southern auroral oval”. Journal of Geophysical Research, 113, A11205, 2008. https://doi.org/10.1029/2008JA013444
Howdy…
In #9, you mentioned the concept of a disc with the North Pole at the centre as a popular flat-earth model, and here this same model is used to show the obvious asymmetry it would create in the auroral ovals. It is also referenced in other proofs posted previously and I expect a lot of future proofs will likely use the same.
So… is the north-centred disc the most credible (gritted teeth) of the flat earth models, sufficiently representative to use as the counter-example for all proofs?
I wouldn’t go so far as “most credible”, but it’s definitely the most commonly proposed configuration of Flat Earth models. It does have a few advantages over other potential flat Earth models, in that the special point of the north pole is mapped to a special point on the flat Earth disc. If you didn’t do that, a lot of the geometry would be even worse and even more difficult to hand-wave away.
I suppose a South-centred disc would function equally well for most proofs, except that the giant unscalable ice cliffs would be replaced by a big bottomless waterfall…?
One other benefit is that nobody lives in the southern hemisphere, and so cannot disprove the theory with a direct flight from Australia to Chile.
Whereas in the north it’s pretty clear that flight times are shorter than they would be with the model flipped. And stuff would be weirder shaped.