Determination of the sun diameter
The radius of the sun can be determined from the pictures. First I fixed its centre from 3 peripheral points (P1, P2, P3) of the sun disk picture. In addition I drew the chords P1 to P2 and P2 to P3. The perpendicular bisector of the sides, established on these chords cut themselves in the centre of the circular disk (see fig. 16).

Fig. 16: Construction of the centre of Sun, Application in the photo

I accomplished this construction method at my photos. From this illustration I determined the radius of the sun picture in the photo to Rs = 78 4 mm. The true sun diameter is calculated using the formula for the photographic eyepiece projection and you get:

The literature value amounts to ds = 1.393*109m. An error of 5 % is amazing, because some "sun eggs" exhibited an extreme eccentricity.