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José M. Vaquero - One of the best experts on this subject based on the ideXlab platform.
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On the Use of Naked-eye Sunspot Observations during the Maunder Minimum
The Astrophysical Journal, 2020Co-Authors: Víctor Manuel Sánchez Carrasco, María Cruz Gallego, Rainer Arlt, José M. VaqueroAbstract:Naked-eye sunspot observations (NESO, hereafter) have been recorded for last two millennia, approximately. This kind of records were made around the world, mainly in Asian civilizations, and they are compiled in several catalogues. In this work, we analyze solar activity in days of the 19th century when NESO were recorded. We found that only more than five sunspot groups were recorded in 39 % of days corresponding to these NESO events. Furthermore, regarding the largest groups observed in days when NESO were reported, we show the uncorrected areas of these groups were below 200 millionths of solar disc (msd hereafter) in 3.2 % of total cases while it is 12.9 % for areas between 200 and 499 msd. Thus, NESO records do not imply high solar activity and big sunspot groups necessarily. Therefore, these results contradict the interpretations of recent works that, using the same NESO set, suggest the solar activity level during the Maunder Minimum is still an open question. NESO records support the Maunder Minimum as a very low solar activity period.
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The umbra-penumbra area ratio of sunspots during the Maunder Minimum
The Astrophysical Journal, 2018Co-Authors: Víctor Manuel Sánchez Carrasco, José M. Vaquero, María Cruz Gallego, J. M. García-romero, P. G. Rodríguez, P. Foukal, Laure LefèvreAbstract:The Maunder Minimum (MM) was a prolonged period of low solar activity that occurred between 1645 and 1715. The true level of solar activity corresponding to this epoch is still a matter of debate. In order to compare solar activity during the MM with that of other epochs, we have evaluated the umbra-penumbra area ratio (U/P hereafter) during the MM. Thus, we have analyzed 196 sunspot drawings including 48 different sunspots observed during the period 1660-1709. The mode value of the ratio obtained from the occurrence frequency distribution lies between 0.15 and 0.25. Furthermore, the median and mean values are equal to 0.24 \pm 0.07 and 0.27 \pm 0.08 with a sigma clipping, respectively. These results are consistent with recent research using more modern data. Higher U/P values mean faster sunspot decay rates. From our results, the almost absence of sunspots during the Maunder Minimum could not be explained by changes in the U/P since the values of the ratio obtained in this work are similar to values found for other epochs.
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Could a Hexagonal Sunspot Have Been Observed During the Maunder Minimum
Solar Physics, 2018Co-Authors: Víctor Manuel Sánchez Carrasco, José M. Vaquero, María Cruz GallegoAbstract:The Maunder Minimum was the period between 1645 and 1715 whose main characteristic was abnormally low and prolonged solar activity. However, some authors have doubted this low level of solar activity during that period by questioning the accuracy and objectivity of the observers. This work presents a particular case of a sunspot observed during the Maunder Minimum with an unusual shape of its umbra and penumbra: a hexagon. This sunspot was observed by Cassini in November 1676, just at the core of the Maunder Minimum. This historical observation is compared with a twin case that occurred recently in May 2016. The conclusion reached is that Cassini's record is another example of the good quality observations made during the Maunder Minimum, showing the meticulousness of the astronomers of that epoch. This sunspot observation made by Cassini does not support the conclusions of Zolotova and Ponyavin (Astrophys. J. 800, 42, 2015) that professional astronomers in the 17th century only registered round sunspots. Finally, a discussion is given of the importance of this kind of unusual sunspot record for a better assessment of the true level of solar activity in the Maunder Minimum.
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Sunspot Observations During the Maunder Minimum from the Correspondence of John Flamsteed
Solar Physics, 2016Co-Authors: Víctor Manuel Sánchez Carrasco, José M. VaqueroAbstract:We compile and analyze the sunspot observations made by John Flamsteed for the period 1672 – 1703, which corresponds to the second part of the Maunder Minimum. They appear in the correspondence of the famous astronomer. We include in an appendix the original texts of the sunspot records kept by Flamsteed. We compute an estimate of the level of solar activity using these records, and compare the results with the latest reconstructions of solar activity during the Maunder Minimum, obtaining values characteristic of a grand solar Minimum. Finally, we discuss a phenomenon observed and described by Stephen Gray in 1705 that has been interpreted as a white-light flare.
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Sunspots during the Maunder Minimum from Machina Coelestis by Hevelius
Solar Physics, 2015Co-Authors: Víctor Manuel Sánchez Carrasco, J. Villalba Álvarez, José M. VaqueroAbstract:We revisited the sunspot observations published by Johannes Hevelius in his book Machina Coelestis (1679) corresponding to the period 1653-1675 (just in the middle of the Maunder Minimum). We show detailed translations of the original Latin texts describing the sunspot records and provide the general context of these sunspot observations. From this source only, we present an estimate of the annual values of the Group Sunspot Number based only on the records that explicitly inform about the presence or absence of sunspots. Although we obtain very low values of the Group Sunspot Number, in accordance with a grand Minimum of solar activity, these values are significantly higher in general than the values provided by Hoyt and Schatten (1998) for the same period.
M C Gallego - One of the best experts on this subject based on the ideXlab platform.
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sunspot characteristics at the onset of the Maunder Minimum based on the observations of hevelius
arXiv: Solar and Stellar Astrophysics, 2021Co-Authors: M C Gallego, Víctor Manuel Sánchez Carrasco, J M Vaquero, Rainer Arlt, Andres Munozjaramillo, G De Toma, P Galaviz, Senthamizh V Pavai, F SanchezbajoAbstract:An analysis of the sunspot observations made by Hevelius during 1642-1645 is presented. These records are the only systematic sunspot observations just before the Maunder Minimum. We have studied different phenomena meticulously recorded by Hevelius after translating the original Latin texts. We re-evaluate the observations of sunspot groups by Hevelius during this period and obtain an average value 7% greater than that calculated from his observations given in the current group database. Furthermore, the average of the active day fraction obtained in this work from Hevelius' records previous to the Maunder Minimum is significantly greater than the solar activity level obtained from Hevelius' sunspot observations made during the Maunder Minimum (70% vs. 30%). We also present the butterfly diagram obtained from the sunspot positions recorded by Hevelius for the period 1642-1645. It can be seen that no hemispheric asymmetry exists during this interval, in contrast with the Maunder Minimum. Hevelius noted a ~3-month period that appeared to lack sunspots in early 1645 that gave the first hint of the impending Maunder Minimum. Recent studies claim that the Maunder Minimum was not a grand Minimum period speculating that astronomers of that time, due to the Aristotelian ideas, did not record all sunspots that they observed, producing thus an underestimation of the solar activity level. However, we show the good quality of the sunspot records made by Hevelius indicates that his reports of sunspots were true to the observations.
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could a hexagonal sunspot have been observed during the Maunder Minimum
Solar Physics, 2018Co-Authors: Víctor Manuel Sánchez Carrasco, J M Vaquero, M C GallegoAbstract:The Maunder Minimum is the period between 1645 and 1715. Its main characteristic is abnormally low and prolonged solar activity. However, some authors have doubted the low level of solar activity during that period by questioning the accuracy and objectivity of the observers. This work presents a particular case of a sunspot observed during the Maunder Minimum with an unusual shape of its umbra and penumbra: a hexagon. This sunspot was observed by Cassini in November 1676, just at the core of the Maunder Minimum. This historical observation is compared with a twin case that occurred recently in May 2016. The conclusion reached is that Cassini’s record is another example of the good quality of the observations that were made during the Maunder Minimum, showing the meticulousness of the astronomers of that epoch. This sunspot observation made by Cassini does not support the conclusions of Zolotova and Ponyavin (Astrophys. J. 800, 42, 2015) that professional astronomers in the seventeenth century only registered round sunspots. Finally, a discussion is given of the importance of this kind of unusual sunspot record for a better assessment of the true level of solar activity in the Maunder Minimum.
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revisited sunspot data a new scenario for the onset of the Maunder Minimum
The Astrophysical Journal, 2011Co-Authors: J M Vaquero, M C Gallego, I G Usoskin, G. A. KovaltsovAbstract:The Maunder Minimum forms an archetype for the Grand minima, and detailed knowledge of its temporal development has important consequences for the solar dynamo theory dealing with long-term solar activity evolution. Here, we reconsider the current paradigm of the Grand Minimum general scenario by using newly recovered sunspot observations by G. Marcgraf and revising some earlier uncertain data for the period 1636-1642, i.e., one solar cycle before the beginning of the Maunder Minimum. The new and revised data dramatically change the magnitude of the sunspot cycle just before the Maunder Minimum, from 60-70 down to about 20, implying a possibly gradual onset of the Minimum with reduced activity started two cycles before it. This revised scenario of the Maunder Minimum changes, through the paradigm for Grand solar/stellar activity minima, the observational constraint on the solar/stellar dynamo theories focused on long-term studies and occurrence of Grand minima.
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A Measure of the Solar Rotation During the Maunder Minimum
Solar Physics, 2002Co-Authors: José M. Vaquero, Florentino Sánchez-bajo, M C GallegoAbstract:In this paper we present a measure of the synodic solar rotation rate derived from an analysis of a Flamsteed drawing, corroborating the decrease of the solar rotation in the deep Maunder Minimum (1666–1700).
G. A. Kovaltsov - One of the best experts on this subject based on the ideXlab platform.
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The Maunder Minimum (1645--1715) was indeed a Grand Minimum: A reassessment of multiple datasets
Astronomy & Astrophysics, 2015Co-Authors: Ilya Usoskin, G. A. Kovaltsov, Kalevi Mursula, Rainer Arlt, Eleanna Asvestari, Ed Hawkins, Maarit J. Käpylä, Natalie A. Krivova, Mike Lockwood, Jezebel O'reillyAbstract:Aims: Although the time of the Maunder Minimum (1645--1715) is widely known as a period of extremely low solar activity, claims are still debated that solar activity during that period might still have been moderate, even higher than the current solar cycle #24. We have revisited all the existing pieces of evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder Minimum. Methods: We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder Minimum. Results: The level of solar activity during the Maunder Minimum is reassessed on the basis of all available data sets. Conclusions: We conclude that solar activity was indeed at an exceptionally low level during the Maunder Minimum. Although the exact level is still unclear, it was definitely below that during the Dalton Minimum around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder Minimum are rejected at a high confidence level.
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revisited sunspot data a new scenario for the onset of the Maunder Minimum
The Astrophysical Journal, 2011Co-Authors: J M Vaquero, M C Gallego, I G Usoskin, G. A. KovaltsovAbstract:The Maunder Minimum forms an archetype for the Grand minima, and detailed knowledge of its temporal development has important consequences for the solar dynamo theory dealing with long-term solar activity evolution. Here, we reconsider the current paradigm of the Grand Minimum general scenario by using newly recovered sunspot observations by G. Marcgraf and revising some earlier uncertain data for the period 1636-1642, i.e., one solar cycle before the beginning of the Maunder Minimum. The new and revised data dramatically change the magnitude of the sunspot cycle just before the Maunder Minimum, from 60-70 down to about 20, implying a possibly gradual onset of the Minimum with reduced activity started two cycles before it. This revised scenario of the Maunder Minimum changes, through the paradigm for Grand solar/stellar activity minima, the observational constraint on the solar/stellar dynamo theories focused on long-term studies and occurrence of Grand minima.
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Revisited sunspot data: A new scenario for the onset of the Maunder Minimum
The Astrophysical Journal, 2011Co-Authors: José M. Vaquero, Ilya Usoskin, María Cruz Gallego, G. A. KovaltsovAbstract:Maunder Minimum forms an archetype for the Grand minima, and detailed knowledge of its temporal development has important consequences for the solar dynamo theory dealing with long-term solar activity evolution. Here we reconsider the current paradigm of the Grand Minimum general scenario by using newly recovered sunspot observations by G. Marcgraf and revising some earlier uncertain data for the period 1636--1642, i.e., one solar cycle before the beginning of the Maunder Minimum. The new and revised data dramatically change the magnitude of the sunspot cycle just before the Maunder Minimum, from 60--70 down to about 20, implying a possibly gradual onset of the Minimum with reduced activity started two cycles before it. This revised scenario of the Maunder Minimum changes, through the paradigm for Grand solar/stellar activity minima, the observational constraint on the solar/stellar dynamo theories focused on long-term studies and occurrence of Grand minima.
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AN UPPER LIMIT ON SUNSPOT ACTIVITY DURING THE Maunder Minimum
Solar Physics, 2004Co-Authors: G. A. Kovaltsov, Ilya Usoskin, Kalevi MursulaAbstract:We have estimated the upper and lower limits of sunspot activity, in terms of active day fraction during the Maunder Minimum (1645–1710), using raw information on individual daily observations (Hoyt and Schatten, 1998). Establishing the relation between the sunspot activity and active day fraction after 1850, we evaluate the upper limit of annual group sunspot number during the deep Maunder Minimum (1645–1700) which does not exceed 4. The earlier finding of a dominant 22-year periodicity during the Maunder Minimum is verified and shown to be robust. Also we confirm that the start of the Maunder Minimum was very abrupt.
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Heliospheric modulation of cosmic rays and solar activity during the Maunder Minimum
Journal of Geophysical Research: Space Physics, 2001Co-Authors: Ilya Usoskin, Kalevi Mursula, G. A. KovaltsovAbstract:Modern models and direct cosmic ray experiments deal with heliospheric modulation of cosmic rays only during the recent times of rather high overall solar activity level. On the other hand, the question of cosmic ray modulation during the exceptional conditions of very quiet heliosphere is important. In the present paper we compare the variations of cosmic ray intensity with solar and auroral activity during the Maunder Minimum (1645-1715) when the Sun was extremely quiet. We use the newly presented group sunspot number series as a measure of early solar activity, the auroral observations in central Europe as an indicator of transient phenomena in the inner heliosphere, and the radiocarbon data as a proxy of cosmic ray intensity. We find that both cosmic ray intensity and auroral activity closely follow the dominant 22-year cyclicity with sunspot activity during the Maunder Minimum. Moreover, the strict antiphase between the 22-year variation of cosmic ray intensity and sunspot activity suggests that the 22-year variation in cosmic ray intensity can be explained by the diffusion-dominated terms of cosmic ray modulation without significant drift effects. We also discuss the possible origin of the behavior of the 10 Be data which is different from all other parameters during the Maunder Minimum.
Ilya Usoskin - One of the best experts on this subject based on the ideXlab platform.
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The Maunder Minimum (1645--1715) was indeed a Grand Minimum: A reassessment of multiple datasets
Astronomy & Astrophysics, 2015Co-Authors: Ilya Usoskin, G. A. Kovaltsov, Kalevi Mursula, Rainer Arlt, Eleanna Asvestari, Ed Hawkins, Maarit J. Käpylä, Natalie A. Krivova, Mike Lockwood, Jezebel O'reillyAbstract:Aims: Although the time of the Maunder Minimum (1645--1715) is widely known as a period of extremely low solar activity, claims are still debated that solar activity during that period might still have been moderate, even higher than the current solar cycle #24. We have revisited all the existing pieces of evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder Minimum. Methods: We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder Minimum. Results: The level of solar activity during the Maunder Minimum is reassessed on the basis of all available data sets. Conclusions: We conclude that solar activity was indeed at an exceptionally low level during the Maunder Minimum. Although the exact level is still unclear, it was definitely below that during the Dalton Minimum around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder Minimum are rejected at a high confidence level.
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Cosmogenic Isotope Variability During the Maunder Minimum: Normal 11-year Cycles Are Expected
Solar Physics, 2014Co-Authors: Stepan Poluianov, Ilya Usoskin, G. A. KovaltsovAbstract:The amplitude of the 11-year cycle measured in the cosmogenic isotope 10Be during the Maunder Minimum is comparable to that during the recent epoch of high solar activity. Because of the virtual absence of the cyclic variability of sunspot activity during the Maunder Minimum this seemingly contradicts an intuitive expectation that lower activity would result in smaller solar-cycle variations in cosmogenic radio-isotope data, or in none, leading to confusing and misleading conclusions. It is shown here that large 11-year solar cycles in cosmogenic data observed during periods of suppressed sunspot activity do not necessarily imply strong heliospheric fields. Normal-amplitude cycles in the cosmogenic radio-isotopes observed during the Maunder Minimum are consistent with theoretical expectations because of the nonlinear relation between solar activity and isotope production. Thus, cosmogenic-isotope data provide a good tool to study solar-cycle variability even during grand minima of solar activity.
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Revisited sunspot data: A new scenario for the onset of the Maunder Minimum
The Astrophysical Journal, 2011Co-Authors: José M. Vaquero, Ilya Usoskin, María Cruz Gallego, G. A. KovaltsovAbstract:Maunder Minimum forms an archetype for the Grand minima, and detailed knowledge of its temporal development has important consequences for the solar dynamo theory dealing with long-term solar activity evolution. Here we reconsider the current paradigm of the Grand Minimum general scenario by using newly recovered sunspot observations by G. Marcgraf and revising some earlier uncertain data for the period 1636--1642, i.e., one solar cycle before the beginning of the Maunder Minimum. The new and revised data dramatically change the magnitude of the sunspot cycle just before the Maunder Minimum, from 60--70 down to about 20, implying a possibly gradual onset of the Minimum with reduced activity started two cycles before it. This revised scenario of the Maunder Minimum changes, through the paradigm for Grand solar/stellar activity minima, the observational constraint on the solar/stellar dynamo theories focused on long-term studies and occurrence of Grand minima.
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AN UPPER LIMIT ON SUNSPOT ACTIVITY DURING THE Maunder Minimum
Solar Physics, 2004Co-Authors: G. A. Kovaltsov, Ilya Usoskin, Kalevi MursulaAbstract:We have estimated the upper and lower limits of sunspot activity, in terms of active day fraction during the Maunder Minimum (1645–1710), using raw information on individual daily observations (Hoyt and Schatten, 1998). Establishing the relation between the sunspot activity and active day fraction after 1850, we evaluate the upper limit of annual group sunspot number during the deep Maunder Minimum (1645–1700) which does not exceed 4. The earlier finding of a dominant 22-year periodicity during the Maunder Minimum is verified and shown to be robust. Also we confirm that the start of the Maunder Minimum was very abrupt.
-
Heliospheric modulation of cosmic rays and solar activity during the Maunder Minimum
Journal of Geophysical Research: Space Physics, 2001Co-Authors: Ilya Usoskin, Kalevi Mursula, G. A. KovaltsovAbstract:Modern models and direct cosmic ray experiments deal with heliospheric modulation of cosmic rays only during the recent times of rather high overall solar activity level. On the other hand, the question of cosmic ray modulation during the exceptional conditions of very quiet heliosphere is important. In the present paper we compare the variations of cosmic ray intensity with solar and auroral activity during the Maunder Minimum (1645-1715) when the Sun was extremely quiet. We use the newly presented group sunspot number series as a measure of early solar activity, the auroral observations in central Europe as an indicator of transient phenomena in the inner heliosphere, and the radiocarbon data as a proxy of cosmic ray intensity. We find that both cosmic ray intensity and auroral activity closely follow the dominant 22-year cyclicity with sunspot activity during the Maunder Minimum. Moreover, the strict antiphase between the 22-year variation of cosmic ray intensity and sunspot activity suggests that the 22-year variation in cosmic ray intensity can be explained by the diffusion-dominated terms of cosmic ray modulation without significant drift effects. We also discuss the possible origin of the behavior of the 10 Be data which is different from all other parameters during the Maunder Minimum.
Víctor Manuel Sánchez Carrasco - One of the best experts on this subject based on the ideXlab platform.
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sunspot characteristics at the onset of the Maunder Minimum based on the observations of hevelius
arXiv: Solar and Stellar Astrophysics, 2021Co-Authors: M C Gallego, Víctor Manuel Sánchez Carrasco, J M Vaquero, Rainer Arlt, Andres Munozjaramillo, G De Toma, P Galaviz, Senthamizh V Pavai, F SanchezbajoAbstract:An analysis of the sunspot observations made by Hevelius during 1642-1645 is presented. These records are the only systematic sunspot observations just before the Maunder Minimum. We have studied different phenomena meticulously recorded by Hevelius after translating the original Latin texts. We re-evaluate the observations of sunspot groups by Hevelius during this period and obtain an average value 7% greater than that calculated from his observations given in the current group database. Furthermore, the average of the active day fraction obtained in this work from Hevelius' records previous to the Maunder Minimum is significantly greater than the solar activity level obtained from Hevelius' sunspot observations made during the Maunder Minimum (70% vs. 30%). We also present the butterfly diagram obtained from the sunspot positions recorded by Hevelius for the period 1642-1645. It can be seen that no hemispheric asymmetry exists during this interval, in contrast with the Maunder Minimum. Hevelius noted a ~3-month period that appeared to lack sunspots in early 1645 that gave the first hint of the impending Maunder Minimum. Recent studies claim that the Maunder Minimum was not a grand Minimum period speculating that astronomers of that time, due to the Aristotelian ideas, did not record all sunspots that they observed, producing thus an underestimation of the solar activity level. However, we show the good quality of the sunspot records made by Hevelius indicates that his reports of sunspots were true to the observations.
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On the Use of Naked-eye Sunspot Observations during the Maunder Minimum
The Astrophysical Journal, 2020Co-Authors: Víctor Manuel Sánchez Carrasco, María Cruz Gallego, Rainer Arlt, José M. VaqueroAbstract:Naked-eye sunspot observations (NESO, hereafter) have been recorded for last two millennia, approximately. This kind of records were made around the world, mainly in Asian civilizations, and they are compiled in several catalogues. In this work, we analyze solar activity in days of the 19th century when NESO were recorded. We found that only more than five sunspot groups were recorded in 39 % of days corresponding to these NESO events. Furthermore, regarding the largest groups observed in days when NESO were reported, we show the uncorrected areas of these groups were below 200 millionths of solar disc (msd hereafter) in 3.2 % of total cases while it is 12.9 % for areas between 200 and 499 msd. Thus, NESO records do not imply high solar activity and big sunspot groups necessarily. Therefore, these results contradict the interpretations of recent works that, using the same NESO set, suggest the solar activity level during the Maunder Minimum is still an open question. NESO records support the Maunder Minimum as a very low solar activity period.
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The umbra-penumbra area ratio of sunspots during the Maunder Minimum
The Astrophysical Journal, 2018Co-Authors: Víctor Manuel Sánchez Carrasco, José M. Vaquero, María Cruz Gallego, J. M. García-romero, P. G. Rodríguez, P. Foukal, Laure LefèvreAbstract:The Maunder Minimum (MM) was a prolonged period of low solar activity that occurred between 1645 and 1715. The true level of solar activity corresponding to this epoch is still a matter of debate. In order to compare solar activity during the MM with that of other epochs, we have evaluated the umbra-penumbra area ratio (U/P hereafter) during the MM. Thus, we have analyzed 196 sunspot drawings including 48 different sunspots observed during the period 1660-1709. The mode value of the ratio obtained from the occurrence frequency distribution lies between 0.15 and 0.25. Furthermore, the median and mean values are equal to 0.24 \pm 0.07 and 0.27 \pm 0.08 with a sigma clipping, respectively. These results are consistent with recent research using more modern data. Higher U/P values mean faster sunspot decay rates. From our results, the almost absence of sunspots during the Maunder Minimum could not be explained by changes in the U/P since the values of the ratio obtained in this work are similar to values found for other epochs.
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Could a Hexagonal Sunspot Have Been Observed During the Maunder Minimum
Solar Physics, 2018Co-Authors: Víctor Manuel Sánchez Carrasco, José M. Vaquero, María Cruz GallegoAbstract:The Maunder Minimum was the period between 1645 and 1715 whose main characteristic was abnormally low and prolonged solar activity. However, some authors have doubted this low level of solar activity during that period by questioning the accuracy and objectivity of the observers. This work presents a particular case of a sunspot observed during the Maunder Minimum with an unusual shape of its umbra and penumbra: a hexagon. This sunspot was observed by Cassini in November 1676, just at the core of the Maunder Minimum. This historical observation is compared with a twin case that occurred recently in May 2016. The conclusion reached is that Cassini's record is another example of the good quality observations made during the Maunder Minimum, showing the meticulousness of the astronomers of that epoch. This sunspot observation made by Cassini does not support the conclusions of Zolotova and Ponyavin (Astrophys. J. 800, 42, 2015) that professional astronomers in the 17th century only registered round sunspots. Finally, a discussion is given of the importance of this kind of unusual sunspot record for a better assessment of the true level of solar activity in the Maunder Minimum.
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could a hexagonal sunspot have been observed during the Maunder Minimum
Solar Physics, 2018Co-Authors: Víctor Manuel Sánchez Carrasco, J M Vaquero, M C GallegoAbstract:The Maunder Minimum is the period between 1645 and 1715. Its main characteristic is abnormally low and prolonged solar activity. However, some authors have doubted the low level of solar activity during that period by questioning the accuracy and objectivity of the observers. This work presents a particular case of a sunspot observed during the Maunder Minimum with an unusual shape of its umbra and penumbra: a hexagon. This sunspot was observed by Cassini in November 1676, just at the core of the Maunder Minimum. This historical observation is compared with a twin case that occurred recently in May 2016. The conclusion reached is that Cassini’s record is another example of the good quality of the observations that were made during the Maunder Minimum, showing the meticulousness of the astronomers of that epoch. This sunspot observation made by Cassini does not support the conclusions of Zolotova and Ponyavin (Astrophys. J. 800, 42, 2015) that professional astronomers in the seventeenth century only registered round sunspots. Finally, a discussion is given of the importance of this kind of unusual sunspot record for a better assessment of the true level of solar activity in the Maunder Minimum.
