Observations by Fabio Colonna
Fabio Colonna (1567–1640) was an Italian naturalist and botanist. We examine his sunspot drawings stored in the archives of the Biblioteca Nazionale Centrale of Florence (BNCF).
1 Aug – 30 Sept 1613
50 sunspot drawings were made by Fabio Colonna (1613) in Naples. Colonna imitated the observations by Galilei (1613). These drawings accompanied the letter to Galilei, where Colonna mentioned that he used the projection technique and the size of the solar disk (disk diameter occupies full page width) is similar to that used in Istoria. Colonna also indicated that his telescope is not good enough to reveal the fine structure (umbra and penumbra) of the sunspots as shown in the book of Galileo (Gargano 2019, for an accurate translation of the letter).
These drawings are reversed in the original publication, therefore we flipped them from top to bottom, which is the natural choice for observations by projecting the Sun behind a Galilean telescope. Images are accompanied by a date and an observing time in hours after sunset. Most of sunspot groups are labeled with Latin letters. On 4 September 1613, Colonna indicated that it was partly cloudy "nebuloso interdu[m]". The drawing of 22 September has a note that on 23 and 24 it was cloudy as well.
3 Oct 1614
On 3 October 1614, Colonna (1614) observed the partial solar eclipse. Colonna's letter, however, does not contain any hint on the type of telescope he used. Gargano (2019) translated the letter to Galilei, where Colonna wrote: "I send you six images of today’s eclipse... marking both the path of the Moon, or better to say of the Sun, which moved rapidly, and the precise sunspots and their size; due to the rush and the little thought I could not do better... Your Lordship will see a very rough sketch; you will be able to recognize the accurate parts, taking what is possible, and you will invert them...".
These schematic and rough drawings are arranged in such a way that the image is conveniently viewed when flipped vertically. It is therefore very likely that Colonna used a Galilean telescope in projection, while a Keplerian telescope was in the process of making at Naples at the same time (Gargano, 2019). The first observation is supplemented by a note "h. 18 ÷", and the last "hor. 19 1/4 ", apparently that is hours after sunset of the previous day. The diameter of the solar disks is of a few centimeters. The second drawing additionally shows the edge of the Moon from the first observation.
In Figure 1, from 14 to 25 September 1613, we systematically define one or two sunspot groups less in comparison with Hoyt abd Schatten (1998). Here, Colonna drew abundant populations of sunspots occupying up to 30o in longitude. Hoyt and Schatten joined sunspots into a larger number of smaller groups, while we join sunspots into a lower number of larger groups.
Figure 2(Top) compares sunspot group latitudes restored by two methods. As usual, the discrepancy lies within 5o (Fig. 2 Bottom).
Fig. 2. (Top) Time-latitude diagrams reconstructed by Methods I and II (Vokhmyanin, Arlt, Zolotova 2021); (Bottom) Latitude discrepancy of two methods.
On the eclipse day of 3 October 1614, to define the observation time in Method I, we compare the transit of the Moon over the solar disk from the report by Colonna with better suited images of the eclipse phases simulated with the CalSky Project (no longer operating) by Arnold Barmettler. The eclipse phase (coverage in percent) on Colonna's third image differs from that calculated by the CalSky by less than 1%. For the second and sixth images, the difference is less than 2%; for the first and fifth mages, slightly more than 4%. On the fourth image, the area covered by the Moon is 11% larger than the coverage from the CalSky. Method II provides average sunspot latitudes, so the observation time is determined by the position angle of the heliographic grid. This results in not sequential time determined by Method II for sequential images.
