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So I've been looking at making a decent calculation of the AU from the 2012 transit. As you can see from the first picture (Taken with the South Pole at the top), this is the method I'm using from the following video:

I use 2*(Pi)/Period of Earth to calculate the angular speed from two points. Afterwards, we multiply that by the change in time to get the angle. Multiplying that by the distance of the Earth from the sun gives us the arc length, which, added to the Diameter of the Earth, equals 2*(Pi)*Change in Time/Period of Venus. Rearranging this equation gives us the AU.

So I have a lot of questions. But please remember that I kinda had to dig a lot of information up myself and have very little experience with astronomy or astrophysics, so if you see something that makes absolutely no sense I apologize in advance. Anyways:

1. I'm not QUITE sure why we add the diameter of the Earth in this case? I know it's the distance between observations, but in this case we need the distance of the Earth between the two points of observation, not necessarily the diameter of the Earth, right?

2. What is the Change in Time exactly? I assume it's the difference between the time for external egress to external ingress for Observers A and the time for external egress to ingress for Observers B. This is usually a 5-13 minutes, right?

3. Where do we take these measurements? At which points on Earth do we need to record the transit for the needed data.? Other solutions I've seen take into account solar parallax, but, from my understanding, they are measured on the same longitude. In this case, we need to have measuring on the same latitudes with very different longitudes, right? Because the measurement is between the first people that see the transit and the last people that do. Sadly, I remembered that the Earth is inclined. So I'm not quite sure what to do at this case.

Anyways, that's basically it. I'm really sorry for the ignorance here but I am very new to this and am having a little bit of trouble understanding everything.

Thanks for the help!

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# Help with Venus Transit AU calculations

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