How to visualize some delicate geometrical problems
with a model.

External view of Sun Earth Venus system :
Earth and Sun centers are in the Ecliptic plane.
Venus center is near of it.
The three points may be aligned or not;

Venus may be slightly upside or downside of the Ecliptic plane.

   Model : conception - CLEA - Francois Sevre (IAP) -   Photos : IAP - Jean Mouette -

As seen from "above", Sun Venus and Earth centers are not aligned thought they are on the Ecliptic plane.

First observers of the transit are at East, but they will not see the whole pheneomenon.

The 1761 observation : Rodriques and Tobolsk are quite on the same meridian.

The white ball represents the Sun
with one sunspot...

As seen from point A, the visible part of the Sun (green line limit)
is smaller than one hemisphere (red line limit).
Another observer, situated in B, will see a different portion of the Sun.
The two observers will see the sunspot in a different position on the solar disk.