Transit duration final explanation: below, two possible configurations among hundreds.
First configuration: Sun is at South, ISS goes from West to East. In this case, the ISS crosses the Sun “laterally” with regard to the observer and the transit duration is the easiest to calculate by hand. Let’s say the distance of ISS to observer is 765 km, at a speed of 8.7 km/s this gives an angular speed of 0.65° per second. The diameter of the Sun being 0.52°, the duration of a central transit is 0.80 second (all those calculations are basic college calculation, no need to detail more). This is the shortest possible duration for a transit at 765 km, but it can be longer in other configurations.
Second configuration, which corresponds to my eclipse transit: Sun is at Est-South-East, the trajectory of the ISS is West-North-West to East-South-East. In this case the ISS does not cross the Sun laterally but is more or less “going away” from the observer. The apparent speed is slower, we have to take into account the angle of view above the horizon (projection of the real speed on celestial vault). The altitude of the Sun being 28.6° at the moment of the transit, the apparent angular speed of configuration 1 has to be multiplied by the sine of 28.6°, therefore the duration of the transit must be divided by the sine of 28.6°, which is 0.48. This gives 0.80 second divided by 0.48 = 1.66 second. Even if Calsky makes a more accurate calculation (taking into account the exact geometry, the roundness of the Earth etc.), its prediction is very close: 1.64 second.
A comparison for configuration 1: I am 100m away from a road and I look at the cars running at 100 km/h. The apparent (angular) speed of a car is maximal when it is passing by me (I see its lateral doors). For configuration 2: I am on the sidewalk of the road and I look at cars 100m from me, approaching or going away at 100 km/h (I see their front or their back). Obviously, their real speed and distance are similar to configuration 1 but their apparent speed is much lower.
simonshack said:
Hence, we have a 207% discrepancy (225-18) between what we should expect in the real world - and what the two astrophotographers claim to be real, authentic imagery of the "ISS" transiting the sun's disc.
So: no discrepancy. Anyway in the real world, with real transits of the real ISS, the only possible discrepancies are the artificial ones created by (your) ignorance.
Dazza’s transit configuration is unknown to me. Comparisons are meaningless if configurations are unknown.
That’s the end of my reply on this forum. I’ll say it as clearly as possible: I’m not in charge of your education about the ISS, you can do it yourself as I did. Telescopes are available to anyone. Cameras are available to anyone. The know-how for solar or lunar transits is available in books and websites. All necessary calculations are already performed by Calsky or Heavens-Above. For less than 1000 euros/dollars and with work and perseverance, after a few months anyone can master the photography of transits. And can make experiments, for example placing two persons 1 or 2 km on each side of a transit line, and from both pictures determine with college level calculation (triangulation) the distance of the ISS to the observers, without any possible discussion. Instead of intellectually masturbating on this forum for years (sorry, I can’t find more appropriate words) and looking in other people’s work for discrepancies that do not exist, why haven’t you already done that? Why don’t you move your ass from your computer and experience the real world, checking ISS passages and transits by yourself? Because you are afraid. Afraid of what you could discover: the existence of the ISS. Then, your imaginary world would collapse.
