Fig. 1. Original sunspot drawings by Cologna on 25 – 27 September 1612 (top) from BNCF, ms. Gal. 95, f. 35r. Orientation of the solar grids corresponds to the time of observation indicated by the observer. Sunspot drawings by Harriot (middle) from ECHO, vol. VIII: spots on the Sun, HMC 241 VIII. The heliographic grid was reconstructed according to the time of observation. Blue ovals define sunspot groups. Flipped drawings by Cologna which match the corresponding solar grids (bottom), Vokhmyanin, Arlt, Zolotova (2021).
Observations by Sigismondo di Cologna
A little is known about Sigismondo di Cologna. We examine his sunspot drawings stored in the archives of the Biblioteca Nazionale Centrale of Florence (BNCF).
6 Sept – 9 Oct 1612
On 10 October 1612, Monreale, Sigismondo di Cologna (1612) sent a series of 21 drawings to Benedetto Castelli. 20 small drawings are of a perfect circle and one rough drawing is an epigraph on the first page. Solar disks are accompanied by a date and an observing time in hours after sunset. Sunspots are labeled with Latin letters. Two drawings on 10 September 1612 were made at 13 and 19 hours after sunset. The style of drawings is similar to that by Scheiner in 1611 and 1612.
We flipped these images from top to bottom, as they are shown reversed in the original publication. Additional comparison of Cologna's drawings with those by Harriot shows that the orientation of some solar disks does not correspond to the indicated time (Figure 1). To fix this: (i) on 10 September 1612 at 19 hours after sunset and on 25 and 26 September, the images were rotated by 90o counter-clockwise, (ii) on 27 September, by 180o, and (iii) on 20 and 21 September (only for Method I), by 50o counter-clockwise.
Figure 2 compares number of groups according to Hoyt and Schatten (1998) and Vokhmyanin, Arlt, Zolotova (2021). On 21 September 1612, there is a big discrepancy. On image of this day by Cologna, we ignore five objects, because they are different in color from darker sunspots. We conclude that those are paper defects. Two of them are tiny, and two medium-size; however, neither appear on previous or subsequent drawings, nor are they present in Harriot's observations. Besides, Cologna did not label them with Latin letters. One more significant discrepancy appears on 6 October 1612. Here, we compare several of Cologna's drawings with Harriot's and assign more groups in comparison to Hoyt and Schatten.
Figure 3 (Top) compares sunspot group latitudes restored by two methods. Due to drawings are small and schematic, there is large discrepancy in results (Fig. 3 Bottom).
Fig. 3. (Top) Time-latitude diagrams reconstructed by Methods I and II (Vokhmyanin, Arlt, Zolotova 2021); (Bottom) Latitude discrepancy of two methods.
