arXiv subjects

J. M. Vaquero

Publications and source records attributed to J. M. Vaquero.

At least 19 recordsLinked to original sources

arXiv2025

Revisiting Christoph Scheiner's Sunspot Records: a New Perspective on Solar Activity of the Early Telescopic Era

Christoph Scheiner was one of the most outstanding astronomers in the history of the sunspot observations. His book, Rosa Ursina, is the reference work regarding the study of the earliest sunspot records. The sunspot observations compiled by Scheiner in Rosa Ursina and Prodomus, including records made by other observers, forms one of the main references of the observations known for that period; particularly around the 1620s. Thus, his work is crucial to determine the solar activity level of the first solar cycles of the telescopic era. The number of sunspot groups recorded in Scheiner's documentary sources has been included in the existing sunspot group number databases. However, we have detected significant errors in the number of groups currently assigned to Scheiner's records. In this work, we reanalyze the information in Scheiner's source documents. Consequently, the standard 11-yr solar cycle shape for the second solar cycle of the telescopic era, which is not clear in previous studies, now becomes evident. In addition, the highest daily number of groups recorded during this cycle (8 groups) is 20% less than the one included in the existing sunspot group number databases. Using the hypergeometrical probability distribution, we find that solar minima in 2008-2009 and 2018-2019 are comparable to the most probable solar activity level of the minimum around 1632. In particular, the estimated lower limit for the solar activity in 1632 is even comparable with the solar activity level in 2008 and 2018.

astro-ph.SR↗

arXiv2025

Strong evidence of low levels of solar activity during the Maunder Minimum

The Maunder Minimum (MM) was a period of prolonged solar activity minimum between 1645 and 1715. Several works have identified a significant number of problematic spotless days in the MM included in existing databases. We have found a list of exact spotless (in the second half of 1709) and spot days (January and August 1709) provided by Johann Heinrich Muller. We computed the most probable value and upper/lower limits of the active day fraction (ADF) from Muller's data using the hypergeometrical probability distribution. Our sample is not strictly random because Muller recorded observations in consecutive days when he observed sunspots. Therefore, our result represents an upper threshold of solar activity for 1709. We compared this result with annual values of the ADF calculated for the Dalton Minimum and the most recent solar cycles. We concluded that it was less active than most years both in the Dalton Minimum and in the most recent solar cycles. Therefore, the solar activity level estimated in this work for 1709 represents robust evidence of low solar activity levels in the MM.

astro-ph.SR↗

arXiv2024

A limit for the values of the Dst geomagnetic index

The study of the extreme weather space events is important for a technological dependent society. Extreme Value Theory could be decisive to characterize those extreme events in order to have the knowledge to make decisions in technological, economic and social matters, in all fields with possible impacts. In this work, the hourly values of the Dst geomagnetic index has been studied for the period 1957-2014 using the peaks-over-threshold technique. The shape parameter obtained from the fit of the generalized Pareto distribution to the extreme values of the |Dst| index leads to a negative value implying an upper bound for this time series. This result is relevant, because the estimation of this limit for the extreme values lead to 850 nT as the highest expected value for this geomagnetic index. Thus, from the previous characterization of the Carrington geomagnetic storm and our results, it could be considered the worst case scenario.

physics.space-ph↗

arXiv2023

José Díaz Bejarano (1933-2019). A Bibliography

José Díaz Bejarano (1933-2019) was born in Puebla de la Calzada (Badajoz, Spain). He studied Chemistry in the University of Seville and Physics in the University of Madrid. Later, he developed a successful research career in several international centers including the University of Hamburg (Germany), CERN (Geneva, Switzerland) or Case Western Reserve University (Cleveland, USA). He returned to Spain to the University of Extremadura, where he did a successful teaching and research work in the Department of Physics (Faculty of Sciences at Badajoz). In this note, a bibliography is provided that contains his publications as well as some news from his life.

physics.hist-ph↗

arXiv2023

Re-calibration of the Sunspot Number: Status Report

We report progress on the ongoing recalibration of the Wolf sunspot number (SN) and Group sunspot number (GN) following the release of version 2.0 of SN in 2015. This report constitutes both an update of the efforts reported in the 2016 Topical Issue of Solar Physics and a summary of work by the International Space Science Institute (ISSI) International Team formed in 2017 to develop optimal SN and GN re-construction methods while continuing to expand the historical sunspot number database. Significant progress has been made on the database side while more work is needed to bring the various proposed SN and (primarily) GN reconstruction methods closer to maturity, after which the new reconstructions (or combinations thereof) can be compared with (a) ``benchmark'' expectations for any normalization scheme (e.g., a general increase in observer normalization factors going back in time), and (b) independent proxy data series such as F10.7 and the daily range of variations of Earth's undisturbed magnetic field. New versions of the underlying databases for SN and GN will shortly become available for years through 2022 and we anticipate the release of next versions of these two time series in 2024.

astro-ph.SR↗

arXiv2022

Observation of large scale precursor correlations between cosmic rays and earthquakes

The search for correlations between secondary cosmic ray detection rates and seismic effects has long been a subject of investigation motivated by the hope of identifying a new precursor type that could feed a global early warning system against earthquakes. Here we show for the first time that the average variation of the cosmic ray detection rates correlates with the global seismic activity to be observed with a time lag of approximately two weeks, and that the significance of the effect varies with a periodicity resembling the undecenal solar cycle, with a shift in phase of around three years, exceeding 6 sigma at local maxima. The precursor characteristics of the observed correlations point to a pioneer perspective of an early warning system against earthquakes.

physics.geo-ph↗

arXiv2022

Visualization of the challenges and limitations of the long-term sunspot number record

The solar cycle periodically reshapes the magnetic structure and radiative output of the Sun and determines its impact on the heliosphere roughly every 11 years. Besides this main periodicity, it shows century-long variations (including periods of abnormally low solar activity called grand minima). The Maunder Minimum (1645-1715) has generated significant interest as the archetype of a grand minimum in magnetic activity for the Sun and other stars, suggesting a potential link between the Sun and changes in terrestrial climate. Recent reanalyses of sunspot observations have yielded a conflicted view on the evolution of solar activity during the past 400 years (a steady increase versus a constant level). This has ignited a concerted community-wide effort to understand the depth of the Maunder Minimum and the subsequent secular evolution of solar activity. The goal of this Perspective is to review recent work that uses historical data to estimate long-term solar variability, and to provide context to users of these estimates that may not be aware of their limitations. We propose a clear visual guide than can be used to easily assess observational coverage for different periods, as well as the level of disagreement between currently proposed sunspot group number series.

astro-ph.SR↗

arXiv2021

Sunspot Records by Antonio Colla just after the Dalton Minimum

Antonio Colla was a meteorologist and astronomer who made sunspot observations at the Meteorological Observatory of the Parma University (Italy). He carried out his sunspot records from 1830 to 1843, just after the Dalton Minimum. We have recovered 71 observation days for this observer. Unfortunately, many of these records are qualitative and we could only obtain the number of sunspot groups and/or single sunspots from 25 observations. However, we highlight the importance of these records because Colla is not included in the sunspot group database as an observer and, therefore, neither his sunspot observations. According to the number of groups, the sunspot observations made by Colla are similar as several observers of his time. For common observation day, only Stark significantly recorded more groups than Colla. Moreover, we have calculated the sunspot area and positions from Colla's sunspot drawings concluding that both areas and positions recorded by this observer seem unreal. Therefore, Colla's drawings can be interpreted such as sketches including reliable information on the number of groups but the information on sunspot areas and positions should not be used for scientific purposes.

astro-ph.SR↗

arXiv2021

Revisiting the Amplitude of Solar Cycle 9: The Case of Sunspot Observations by W.C. Bond

William Cranch Bond, director of the Harvard College Observatory in mid-19th century, carried out detailed sunspot observations during the period 1847-1849. We highlight Bond was the observer with the highest daily number of sunspot groups observed in Solar Cycle 9 recording 18 groups on 26 December 1848 according to the current sunspot group database. However, we have detected significant mistakes in these counts due to the use of sunspot position tables instead of solar drawings. Therefore, we have revisited the sunspot observations made by Bond, establishing a new group counting. Our new counts of the sunspot groups from Bond's drawings indicate that solar activity was previously overestimated. Moreover, after this new counting, Bond would not be the astronomer who recorded the highest daily group number for Solar Cycle 9 but Schmidt with 16 groups on 14 February 1849. We have also indicated the new highest annual group numbers recorded by any observer for the period 1847-1849 in order to correct those values applied in the "brightest star" method, which is used as a rough indicator of the solar activity level. Furthermore, a comparison between Bond's sunspot records and the sunspot observations made by Schwabe and Wolf is shown. We conclude that the statistics of Wolf and Bond are similar regarding to the group count. Additionally, Schwabe was able to observe smaller groups than Bond.

astro-ph.SR↗

arXiv2021

Soonspot: Software to Determine Areas and Sunspot Positions

A new software (Soonspot) for the determination of the heliographic coordinates and areas of sunspots from solar images is presented. This program is very user-friendly and the accuracy of its results has been checked by using solar images provided by the Debrecen Photoheliographic Data (DPD). Due to its applicability in the studies of historical solar observations, the program has been used to analyze the solar drawings carried out by Hevelius in the 17th century.

astro-ph.SR↗

arXiv2021

Eric Strach: four decades of detailed synoptic solar observations (1969-2008)

Eric H. Strach (1914-2011) studied medicine at University of Prague and graduated in 1938. Strach dedicated a great part of his life to astronomy becoming a consistent and meticulous observer. He joined the Liverpool Astronomical Association and British Astronomical Association during the 1960s and obtained two recognitions as proof of his great work in solar physics: the BAA's Merlin Medal and Gift in 1999 and Walter Goodacre Medal and Gift, ten years later. Strach recorded four decades (1969-2008) of systematic solar records in his observation notebooks although he started his observations from the late 1950s. In this work, we document the valuable effort made by Strach in getting four decades of solar records and the importance of this kind of long observation series for studies of space weather and climate. We present the sunspot group number series according to Strach's data and a long observation series of prominences recorded by Strach.

astro-ph.SR↗

arXiv2021

Portuguese eyewitness accounts of the great space weather event of 1582

Newly discovered descriptions about the great aurora observed in March 1582 are presented in this work. These records were made by Portuguese observers from Lisbon. Both records described the aurora like a great fire in the northern part of the sky. It was observed during three consecutive nights, according to one of the sources. Thus, we present a discussion of these auroral records in order to complement other works that studied the aurora sighted in March 1582.

physics.pop-ph↗

arXiv2021

Number of Sunspot Groups from the Galileo-Scheiner controversy revisited

We revise the sunspot observations made by Galileo Galilei and Christoph Scheiner in the context of their controversy on the nature of sunspots. Their sunspot records not included in the current sunspot group database, used as a basis to calculate the sunspot group number, are analyzed. Within the documentary sources consulted in this work, we can highlight the sunspot observations by Scheiner included in the letters sent under the pseudonym Apelles to Marcus Welser and the first sunspot observations made by Galileo, which can be consulted in Le opere di Galileo Galilei. These sunspot observations would extend the temporal coverage for these two observers and filling some gaps in the current group database in the earliest period where the data available is sparse. Moreover, we have detected changes in the quality of the sunspot drawings made by Galileo and Scheiner in their observation series affecting to the number of groups recorded by the two observers. We also compare these records with sunspot observations made by other astronomers of that time. According to this comparison and regarding the same observation days, Scheiner was generally the astronomer who reported more sunspot groups while Harriot, Cigoli, and Galileo recorded a similar number of groups. We conclude these differences are mainly because of the observational method used by the observers.

astro-ph.SR↗

arXiv2021

Sunspot observations by Charles Malapert during the period 1618-1626: a key dataset to understand solar activity before the Maunder minimum

A revision is presented of the sunspot observations made by Charles Malapert from 1618 to 1626, studying several documentary sources that include those observations. The revised accounting of the group numbers recorded by Malapert for that period shows new information unavailable in the current sunspot group database. The average solar activity level calculated from these revised records of Malapert is by almost one third greater than that calculated from his records included in the current group database. Comparison of the sunspot observations made by Malapert and by other astronomers of that time with regard to the number of recorded groups and sunspot positions on the solar disk shows good agreement. Malapert reported that he only recorded one sunspot group in each sunspot drawing presented in Austriaca Sidera Heliocyclia (the documentary source which includes most of the sunspot records made by Malapert), although he sometimes observed several groups. Therefore, the sunspot counts obtained in this present work on Malapert's sunspot observations represents the lower limit of the solar activity level corresponding to those records.

astro-ph.SR↗

arXiv2021

Sunspot characteristics at the onset of the Maunder Minimum based on the observations of Hevelius

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.

astro-ph.SR↗

arXiv2021

Sunspot Catalogue of the Observatory of the University of Coimbra (1929-1941)

A sunspot catalogue was published by the Coimbra Astronomical Observatory (Portugal), now named Geophysical and Astronomical Observatory of the University of Coimbra, for the period 1929-1941. We digitalized data included in that catalogue and provide a machine-readable version. We show the reconstructions for the (total and hemispheric) sunspot number index and sunspot area according to this catalogue, comparing it with the sunspot number index (version 2) and Balmaceda sunspot area series (Balmaceda et al., J. Geophys. Res. 114, A07104, 2009). Moreover, we also compared the Coimbra catalogue with records made at the Royal Greenwich Observatory. The results demonstrate that the historical catalogue compiled by the Coimbra Astronomical Observatory contain reliable sunspot data and therefore can be considered for studies about solar activity.

astro-ph.SR↗

arXiv2020

On the use of naked-eye sunspot observations during the Maunder Minimum

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.

astro-ph.SR↗

arXiv2018

A Sunspot Catalog for the Period 1952-1986 from Observations Made at the Madrid Astronomical Observatory

Sunspot catalogs are very useful for studying the solar activity of the recent past. In this context, a catalog covering more than three solar cycles made by the astronomers of the Madrid Astronomical Observatory in Spain (nowadays, the National Astronomical Observatory) from 1952 until 1986 has been recovered. Moreover, a machine-readable version of this catalog has been made available. We have recovered abundant metadata and studied the reliability of this dataset by comparing it with other sunspot catalogs.

astro-ph.SR↗