Fig. 1. Estimated range of sunspot positions from 22 February to 6 August 1660. The blue, red, and green regions represent the three sunspot groups. Areas without fill indicate positions that were not confirmed by the observations. L0 denotes the heliographic longitude of the apparent disk center as seen from Gdansk, Poland (Zolotova and Vokhmyanin 2025).
Observations by Johannes Hevelius
Johannes Hevelius (1611–1687) was a Polish astronomer based in Danzig (Gdańsk). He worked from his own privately funded observatory. Known to belong to a noble family, Hevelius was a city councilor and brewer.
22 February – 7 August 1660
The following text employs observations published in book Machina Coelestis (1679). The observations cover the period of 1653 – 1675, but we only consider the period of 22 February – 7 August 1660. We rely on the translation of the original Latin text by Carrasco, Alvarez, and Vaquero (2015).
Speculating that the sunspots or sunspot groups could have persisted for seven solar rotations due to weakened convection✱, we modeled the transit of two objects (reported by Rober Boyle) across the solar disk between February and August 1660. The rotation rate for the first sunspot (in blue) is 14.4 ± 0.1o d-1. For the second sunspot (in red), whose rotation rate is unknown, we applied the rotation law derived by Balthasar, Vazquez, and Woehl (1986): ω(B) = ω0 + 2.87 sin2B, where B represents the heliographic latitude, and ω0 is set to 14.4 ± 0.1o d-1.
The colored regions in Figure 1 represent the estimated latitude-longitude ranges, where the centers of the sunspot groups could have been located. Repeat that the reference points for these estimations are Boyle's observations on 7 May and 4 June 1660 for the first (in blue) and the second (in red). To match the assumed range of sunspot positions with text reports made by Hevelius (1679) in 1660, Figure 1 shows the heliographic grid as it was seen in Gdansk, Poland, at local Noon (10:45 UT). However, it is not strictly that the sunspots were observed at Noon.
In Machina Coelestis, Hevelius provided astrometric and solar observations in tabular form. The solar observations primarily consist of midday altitude measurements, with less focus on sunspot reports and solar diameter measurements. The tables also document the equipment used, weather conditions, and the quality of the observations. Notably, only an azimuthal quadrant or horizontal quadrant is mentioned in these records. If a telescope was not utilized, the observer would have been limited to detecting large sunspots. However, Hevelius made a single mention of observing faculae, which suggests that a refracting telescope was employed.
On 22 February 1660, Hevelius reported a notable round spot that appeared in the middle of the solar disk, with a smaller spot that corresponds to the assumed range of sunspot positions shown in Figure 1a. The sunspot would have been exactly at the center, given a rotation rate of 14.45o d-1. This faster rotation, compared to the 14.4o d-1 rate, could be attributed to uncertainties or to the tendency of the rotation rate of long-lived recurrent sunspot groups to slow down over time (Pulkkinen and Tuominen, 1998, Figure 9 therein). In contrast, Kutsenko, Abramenko, and Litvishko (2023) inferred that the rotation rate remains constant throughout the evolution of an active region. Furthermore, the area-weighted center of an active region may exhibit its own motion as the region evolves, introducing additional uncertainties in rotation rate (Petrovay, 1993).
On 26 February 1660, Hevelius reported that the larger spot had shrank and the smaller one had vanished. On 29 February, faint faculae and umbrae were observed✱✱. According to our calculations, the large sunspot should have already been a few to 15o behind the western limb on that day. Therefore, Hevelius could have observed smaller following spot(s), if any were behind the preceding spot, or it could have been another active region.
On 16 March 1660, Hevelius observed the spot along with two smaller ones near the eastern limb. He also assumed that the sunspots showed up on 13 or 14 March. This report is consistent with our calculations (Figures 1b and c). On 13 March, the sunspot, rotating at 14.35o d-1, is estimated to have been at the very edge of the solar disk. If it had been rotating faster, the spot would have still remained behind the limb. If the rotation rate exceeded 14.55o d-1, the sunspot would still have been behind the limb even on 14 March. On 17 March, Hevelius reported that the major sunspot had grown and was followed by five smaller and faint spots. On 21 March 1660, the spots were observed in the western quadrant. Finally, on 28 March, no spots were reported. Both entries align with our proposed sunspot positions: Figure 1d and on 28 March, the sunspots were 19 − 275o beyond the limb.
On 11 and 20 April 1660, Hevelius described the solar disk as being blank. According to our calculations, the supposedly long-living sunspot was located near the eastern and western limbs, respectively (Figures 1e and f; here and below, in cases where the assumed range of sunspot positions is not confirmed by observations, we have omitted the color fill). Since the observations on 11 April were made diligently, as Hevelius noted in the relevant column of his table, we can speculate that the sunspot group lived only two solar rotations (February and March 1660). Moreover, at the beginning of the second rotation, Hevelius reported that the spot had enlarged, which is unlikely for a spot that has persisted for more than one rotation. This could be interpreted as the emergence of a new portion of magnetic flux.
On 12 May 1660, Hevelius stated a conspicuous round spot near the center of the Sun, which had already passed the disk center by the next day. He also suggested that it crossed the eastern limb around 6 May. By 15 May, the spot had shrunk, and by 18 May, it was close to the western limb. The following day, the spot had already exited the solar disk. These reports align precisely with Boyle's observations and our estimations: on 6 May, the sunspot was a few degrees from the eastern limb; on 12 May, it was near the disk center (Figure 1g); and by 19 May, it had just passed the limb.
On 2 June 1660, Hevelius reported that no sunspots were detected. However, according to our assumptions, the center of the active region should have been located at the very edge of the eastern limb.
On 10 June 1660, Hevelius described notable sunspots: three near the center of the Sun and one in the western quadrant. This observation agrees with Boyle’s observations and our calculations: the center of the first sunspot was in the western quadrant, while the second active region was near the disc center (Figure 1h, blue and red, correspondingly). Since the exact position of the second spot relative to the Equator is unkown, the red stripe occupies both hemispheres. Hevelius also reported sunspots on 11 and 12 June, and by 16 June, no spots were observed. We estimate that the center of the second active region would have been at the very edge of the solar disk on 16 June.
On 9 July 1660, Hevelius noticed a large round sunspot, along with a smaller one near the southwestern limb. He suggested the group had entered the solar disk about 10 days earlier. This description matches the range of sunspot positions that we have marked in blue (Figures 1i and j). On 30 June, the active region, which we marked in red, was still behind the eastern limb, and by 9 July, it would not have been near the limb yet (Figure 1j). Therefore, we conclude that the red sunspot did not become recurrent since its first appearance on 4 June.
On 12 July 1660, Hevelius reported that the spots had clearly disappeared, albeit another smaller spot along with a few tiny ones with umbrae, was observed near the eastern limb. On that day, we calculated that the center of the active region, which we marked in blue, was already beyond the limb. If the spot, which we marked in red (Figure 1k), was still alive, it would have been near the edge of the disc, contrary to Hevelius's description. The assumed latitude – longitude range of a new sunspot group near the eastern limb is shown in green (Figure 1k). On 13 July, Hevelius noted that the spots had weakened by the afternoon, and by 19 July, the solar disk was blank.
On 27 July 1660, Hevelius reported the solar disk was absolutely clear. The following day, however, he observed a round spot near the eastern limb, which he claimed had entered the Sun on the day before for the first time. These two notes seem to contradict each other. Figure 1l shows the possible location of the sunspot on 27 July (blue); the color fill is removed, as Hevelius noted that no spots were visible on that day. Here and further, we extend the assumed latitude range into the northern hemisphere because Hevelius mentioned that this was the first time he observed the spot, with the hemisphere unspecified. On the next day (Figure 1m), only the assumed latitude – longitude range of the sunspot (blue) matches the observation by Hevelius. If the spot marked in red were still visible, it would have been located at the very edge of the disc on 28 July, which contradicts Hevelius’s description.
On 31 July 1660, Hevelius reported that the spot remained near the center of the Sun. On 3 August, the spot had moved into the western quadrant. On 6 August, a much smaller spot appeared near the western limb, and by 7 August, the spot was still visible on the Sun. Figures 1n, o, and p show that only the assumed positions of the spot, marked in blue, agree with these observations. Therefore, the sunspot group first observed by Boyle on 4 June 1660 (Figure 1c therein, red arc) was not a long-lived object after all.
In conclusion, we find that from 22 February to 7 August 1660, the object marked in blue (Figure 1) was not the same long-lived recurrent sunspot group, but rather an activity nest✱✱✱ that persisted through several rotations. The first active region, or regions, within this nest were observed over two solar rotations from 22 February to 22 March 1660. A new portion of magnetic flux, emerging as a separate active region, was observed over three rotations from 7 May to 9 July 1660. Another active region, or regions, within this nest lived from 28 July to 7 August 1660. However, its latitudinal position was not specified, so it is possible that this active region belonged to the opposite hemisphere.
The object marked in red (Figure 1) was observed for one rotation on 4 – 12 June 1660. One more sunspot group, marked in green, was reported on 12 and 13 July 1660. In total, we identified at least five distinct sunspot groups. The sunspot parameters, as derived from our assumption about the drawings, are provided in the Electronic Supplementary Materials.
Modern studies have shown that found that an activity nest can live from 6 up to 15 solar rotations Castenmiller, Zwaan, and van der Zalm (1986). Henwood, Chapman, and Willis (2010) found that only two sunspot nestlets lasted for over nine solar rotations, while five nestlets persisted for eight rotations. The discrepancies in these findings seem to stem from differences in the criteria used to identify a pair of sunspot groups as recurrent.